|USFDC Home | USF Electronic Theses and Dissertations||| RSS|
This item is only available as the following downloads:
xml version 1.0 encoding UTF-8 standalone no
record xmlns http:www.loc.govMARC21slim xmlns:xsi http:www.w3.org2001XMLSchema-instance xsi:schemaLocation http:www.loc.govstandardsmarcxmlschemaMARC21slim.xsd
leader nam 2200397Ka 4500
controlfield tag 001 002006316
007 cr mnu|||uuuuu
008 090610s2008 flu s 000 0 eng d
datafield ind1 8 ind2 024
subfield code a E14-SFE0002716
Hintz, Amanda Rachelle.
Physical volcanology and hazard analysis of a young monogenetic volcanic field :
b Black Rock desert, Utah
h [electronic resource] /
by Amanda Rachelle Hintz.
[Tampa, Fla] :
University of South Florida,
Title from PDF of title page.
Document formatted into pages; contains 142 pages.
Thesis (M.S.)--University of South Florida, 2008.
Includes bibliographical references.
Text (Electronic thesis) in PDF format.
ABSTRACT: The Black Rock volcanic cluster consists of 30 small volume monogenetic volcanoes. The volcanoes of this cluster have exhibited bimodal volcanism for > 9 Ma. The most recent eruption of Ice Springs volcano ~600 yrs. ago along with ongoing geothermal activity attests to the usefulness of a hazard assessment for this area. The likelihood of a future eruption in this area is estimated to be between a 0.16 and 24% chance over the next 1 Ka (95% confidence). The explosivity and nature of many of these eruptions is not well known. In particular, the physical volcanology of Tabernacle Hill suggests a complicated episodic eruption. Initial phreatomagmatic eruptions at Tabernacle Hill are reported to have begun no later than ~14 Ka. The initial eruptive phase produced a tuff cone approximately 150 m high and 1.5 km in diameter with distinct bedding layers.Recent mapping and sampling of Tabernacle Hill's lava and tuff cone deposits was aimed at better constraining the sequence of events, physical volcanology, and energy associated with this eruption. Blocks located on the rim of the tuff cone of were mapped and analyzed to yield preliminary minimum muzzle velocities of 60-70 m s. After the initial phreatomagmatic explosions, the eruption style transitioned to a more effusive phase that partially filled the tuff cone with a semi-steady state lava lake 200 m wide and 15 m deep. Eventually, the tuff cone was breached by the impinging lava resulting in large portions of the cone rafting on top of the lava flows away from the vent. Eruption onto the Lake Bonneville lake bed allowed the Tabernacle Hill lava flows to flow radially from the tuff cone and cover an area of 19.35 km, producing a very uniform high aspect ratio (100:1) flow field.Subsequent eruptive phases cycled several times between effusive and explosive, producing scoria cones and more lava flows, culminating in an almost complete drainage of the lava lake through large lava tubes and drain back.
Mode of access: World Wide Web.
System requirements: World Wide Web browser and PDF reader.
Co-advisor: Charles B. Connor, Ph.D.
Co-advisor: Paul Wetmore, Ph.D.
t USF Electronic Theses and Dissertations.
Physical Volcanology and Hazard Analysis of a Young Monogenetic Volcanic Field: Black Rock Desert, Utah by Amanda Rachelle Hintz A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science Department of Geology College of Arts and Sciences University of South Florida Co Major Professor: Charles B. Connor, Ph.D. Co Major Professor: Paul Wetmore, Ph .D. Diana Roman, Ph.D. Date of Approval: March 27, 2008 Keywords: Intraplate volcanism tuff cone, ballistic analysis probabilistic analysis hydrovolcanism Quaternary volcanism Copyright 2008, Amanda Rachelle Hintz
Dedication for Clyde
Acknowledgements Financial support during my graduate studies was provided by the Volcanology Research Group at the University of South Florida, a teaching assistantship from the Department of Geology, and the IAVCEI Grant in Aid Scholarship. I owe the greatest thanks to my thesis advisor, Dr. Charles B. Connor, for his engaging approach in teaching, his patience, guidance, encouragement, the time he invested in me and this project and his helpful suggestions during the course of my research and preparat ion for this thesis. I would also like to thank my committee members, Dr. Paul Wetmore and Dr. Diana Roman for their time, advice and editing. I would like to extend my appreciation to Dr. Larry Mastin for his advice regarding the ballistics portion of thi s thesis. I thank my lovely officemates, Sophie Pearson, Alain Volentik, and Dr. Mikel Diez for all their advise, (ah hem) patience, and worldly views. I would like to extend my most sincere and intimate thank you to my husband Nik. I am forever indebted to you for all your emotional, mental, and culinary support for the past several years. I would also like to attempt to thank my grandp arents for all their emotional (and financial) support they have given over the years. Through their love and understanding I have achieved already so much more than a life i n show business had to offer.
i Table of Contents List of Tables iii List of Figures iv Abstract ix Chapter 1: Introduction 1 1.1 Objectives 5 1.2 Geographical Setting 6 1.3 Previous Work 9 1.4 Overview of Methods 11 Chapter 2: Tabernacle Hill 12 2.1 Legend of the Map and General Stratigraphy 14 2.2 Description of the Map Units 16 2.3 Eruptive History 48 Chapter 3: Ballistic Analysis 55 3.1 Background and Previous Works 57 3.2 Sampling and Characterization 58 3.3 Analysis 62 3.3.1 Methods 63 3.3.2 Governing Equations 64 3.4 Results 70 3.4.1 Drag Comparison 70 3.4.2 Analytical 72 3.4.3 Numerical 74 3.5 Discussion 78 Chapter 4: Rates of Volcanism 79 4.1 Summary of Volcanism in the Black Rock Cluster 79 4.2 Rates and Hazard Analysis 106 4.3 Evolution of the Black Rock Volcanic Cluster 117 Chapter 5: Conclusions 120 References 122
ii Appendices 129 A.1 Geologic Map of Tabernacle Hill Volcano 130 A.2 Geologic Map of the Tabernacle Hill Crater 131 A.3 Geologic Cross-Sections of Tabern acle Hill Volcano 132 A.4 Illustrated Stratigraphic Section of Tabernacle Hill Volcano 133 A.5 Geologic Map of the Black Rock Volcanic Cluster 134 A.6 Physical attributes and geochemical reference for the Black Rock Volcanic Cluster 135 A.7 Black Rock Volcanic Cluster Vent Locations 137 A.8 Ballistic Analysis Codes 138 A.9 Variables 139 A.10 Ballistic Data 140 A.11 TAS Diagram for the Black Rock Volcanic Cluster 142
iii List of Tables Table 3.1 Initial velocity results for analytical solutions for several representative blocks on Tabernacle Hill evaluated from Figure 3.8 using Equations 3.10 and 3.15. 74 Table 3.2 Results for numeral solutions for four blocks erupted at four different ejection angles, where; vi is initial velocity, t is total time of flight and E is the maximum elevation achieved by the blocks. 76 Table 3.3 Data from Figure 3.10. where vi is the initial velocity, xf is the computed range, t is the total travel time of the block, and E is the maximum elevation achieved during the flight 78 Table 4.1 Physical characteristics of several monogenetic volcanic fields. 118
iv List of Figures Figure 1.1 Location Map of the Black Rock Desert, Utah. 3-4 Figure 1.2 Shaded topographic relief ma p of Utah. 7 Figure 2.1 Geologic maps of Tabernacle Hill volcano. 14-15 Figure 2.2 Simplified geologic map of Tabernacle Hill volcano showing the four main outcrops of volcanic tuff. 17 Figure 2.3 View of the Tabernacle Hill tuff cone. 19 Figure 2.4 Illustration of the large in situ portion of the tuff cone and locations of strike and dip measurements. 20 Figure 2.5 Photo showing non-indurate d partially palagonitized tuff and scour and fill structure. 21 Figure 2.6 Photograph of an armored accr etionary lapilli mantled by a very thin coating of desert caliche 22 Figure 2.7 Photograph from the summit of the tuff cone showing a large Type 1 bomb. 24 Figure 2.8 Photograph of a large Type 2 block entrained in a very indurated section of the tuff cone. 25 Figure 2.9 Photograph of two large bloc ks near the lower portion of the tuff cone. 26 Figure 2.10 Simplified geologic map of the crater of Tabernacle Hill volcano showing the distribution of lava lake deposits. 27 Figure 2.11 Photograph of the Tabern acle Hill crater, site of the former lava lake, looking south. 28
v Figure 2.12 Simplified geologic map highlighting the extent of the lava flows. 30 Figure 2.12 Photograph looking south from th e tuff cone at the block and bomb distribution (mostly Type 2s seen here) and tumuli fields in the background. 31 Figure 2.13 Distal edge of Tabern acle Hill lava flow (P lf) near the south end. 31 Figure 2.14 Photograph showing peperitic tufa entrained by pillow basalts on the distal edges of the Tabernacle Hill lava flow. 32 Figure 2.15 Simplified geologic maps of Tabernacle Hill highlighting the locations of scoria deposits. 32 Figure 2.16 Photograph looki ng east at the two large scoria cones on the east rim of the central crater. 35 Figure 2.17 Photograph of a sediment ary xenolith (Q lf) encased by oxidized cinder of the scoria cone. 36 Figure 2.18 Photograph of agglutinated scoria (Psc) observed at the south end of the Tabernacle Hill lava flow. 36 Figure 2.19 Photographs showing the a dditional scoria deposit located within the main in situ section of the tuff cone. 38 Figure 2.20 Simplified geologic map of Tabernacle Hill volcano highlighting the locations of lava tube collapses. 39 Figure 2.21 Photograph of the interior of one of many large lava tubes that remain uncollapsed. 40 Figure 2.22 Photograph looking north at the largest lava tube observed on Tabernacle Hill. 40 Figure 2.23 Simplified geologic map of the crater area of Tabernacle Hill highlighting the locations of the crater rim rubble piles. 41 Figure 2.24 Photograph showing the outward dipping edges of the southwestern side of the crater rim a nd adjacent rubble. 42
vi Figure 2.25 Simplified geologic map highlighting the rheomorphic lava lake deposits. 43 Figure 2.26 Photograph showing the f eatures in the southern portion of the central crater. 44 Figure 2.27 Simplified geologic map of th e crater area of Tabernacle Hill highlighting the various locations of intr a-crater rubble piles. 45 Figure 2.28 Photographs showing the st acked structure of some of the intra-crater rubble. 46 Figure 2.29 Photograph of pillow basalts with tu fa deposits between them. 47 Figure 2.30 Inferred cross section th rough Tabernacle Hill corresponding to lines A and B in Appendix A.1. 49 Figure 2.31 Inferred cross section th rough Tabernacle Hill corresponding to lines A and B in Appendix A.1 52 Figure 2.32 Photograph showing the northern rheo morphic piece of tuff cone. 53 Figure 3.1 Shaded relief map of Tabernac le Hills tuff cone showing the locations of the 74 blocks mapped for this study 59 Figure 3.2 View of Tabernacle Hill tuff cone looking north-northeast at the inner flank of the tuff cone 60 Figure 3.3 Image of an in situ block on top of the Tabernacle Hill tuff cone looking west-southwest. 61 Figure 3.4 Large Type 1 block on the rim of Tabernacle Hill tuff cone looking north. 61 Figure 3.5 The relationship between all 74 measur ed blocks on Tabernacle. 66 Figure 3.6 Effect of several drag coefficients on initial velocity. 71 Figure 3.7 Graphical representation to the analytical solutions from equations 3.11 and 3.16. 72 Figure 3.8 Block flight traj ectories for Blocks 1, 38, 63 and 64. 75 Figure 3.9 Graphical results for calculated range of several blocks under the conditions of zero drag. 76
vii Figure 4.1 Simplified geologic locati on map of the Quaternary Black Rock volcanic cluster and surrounding features. 82 Figure 4.2 Cumulative event curve fo r the Black Rock volcanic cluster based on data in Appendix A.6. 83 Figure 4.3 Graphical illustration of the cumulative volcanic vents and relative area over time. 84 Figure 4.4 Simplified geologic maps of the Blac k Rock volcanic cluster. 86 Figure 4.5 Simplified geologic ma p highlighting the volcanism associated with the Beaver Ridge eruptions. 89 Figure 4.6 Simplified geologic map of the Blac k Rock volcanic field. 90 Figure 4.7 Photograph showing the easte rn flow front of the Black Rock volcanic flow. 91 Figure 4.8 Simplified geologic map of the Kanosh volcanic field (Black Rock volcano). 92 Figure 4.9 Photograph of the main ve nt complex of the highly eroded Kanosh volcano. 92 Figure 4.10 Simplified geologic ma p highlighting the volcanism associated with the Cove Fort area of the BRVC 94 Figure 4.11 Photograph showing a rhyolitic rock from White Mountain found in the Tabernacle Hill tuff cone. 95 Figure 4.12 Simplified geologic map highlightin g the Deseret volcano. 96 Figure 4.13 Simplified geologic map of the Sme lter Knoll volcanic field. 97 Figure 4.14 Aerial photograph show ing the eroded remnant of a phreatic basaltic crater in the foreground and the rhyolite domes of the Smelter Knolls in the background. 98 Figure 4.15 Simplified geologic map of the Pahvant volcanic field 100 Figure 4.16 Photograph showing the west faci ng side of Pahvant Butte 101 Figure 4.17 Simplified geologic map of Ta bernacle Hill volcano. 102
viii Figure 4.18 Simplified geologic map of the I ce Springs volcanic field. 104 Figure 4.18 Graph showing the abso lute volumes of the volcanic deposits in the BRVF over time. 104 Figure 4.19 Empirical survivor func tion of the repose intervals, ti, preceding eruptions from the data set in Appendix A.6, as a function of the repose interval. 108 Figure 4.20 The empirical survivor function graphed in Figure 4.20 showing the relative volume and compositions of the BRVC events as a function of their so rted repose intervals. 109 Figure 4.21 Survivor function for the entire BRVC 111 Figure 4.22 Survivor function for BRVC Episode I 112 Figure 4.23 Survivor function for BRVC Episode II 113 Figure 4.24 Survivor function for BRVC Episode III 114
ix Physical V olcanology and H azard A nalysis of a Y oung M onogenetic V olcanic F ield: Black Rock Desert, Utah Amanda Hintz ABSTRACT The Black Rock volcanic cluster consists of 30 small volume monogenetic volcanoes. The volcanoes of this cluster have exhibited bimodal volcanism for > 9 Ma. The most recent eruption of Ice Springs volcano ~600 yrs. ago along with ongoing geothermal activi ty attests to the usefulness of a hazard assessment for this area. The likelihood of a future eruption in this are a is estimated to be between a 0.16 and 24% chance over the next 1 Ka (95% confidence) The explosivity and nature of many of these eruptions is not well known. In particular, the physical volcanology of Tabernacle Hill suggests a complicated episodic eruption. Initial phreatomagmatic eruptions at Tabernacle Hill are reported to have begun no later than ~14 Ka. The initial eruptive phase produced a tuff c one approximately 150 m high and 1.5 km in diameter with distinct bedding layers. Recent mapping and sampling of Tabernacle Hills lava and tuff cone deposits was aimed at better constraining the sequence of events physical volcanology and ener gy associated with this eruption. Blocks located on the rim of the tuff cone of were mapped and analyzed to yield preliminary minimum muzzle velocities of 6070 m s1. After the initial phreatomagmatic explosions, the eruption style transitioned to a more effusive phase that partially filled the tuff cone with a semisteady state lava lake 200 m wide and
x 15 m deep. Eventually, the tuff cone was breached by the impinging lava resulting in large portions of the cone rafting on top of the lava flows away from the vent. Eruption onto the Lake Bonneville lake bed allowed the Tabernacle Hill lava flows to flow radially from the tu ff cone and cover an area of 19.35 km2, producing a very uniform high aspect ratio (100:1) flow field. Subsequent eruptive phases cycle d several times between effusive and explosive, producing scoria cones and more lava flows, culminating in an almost complete drainage of the lava lake through large lava tubes and drain back
1 Chapter 1 Introduction The main aim of this project was to study the volcanic evolution of the Black Rock and Sevier Deserts by better understanding how volcanism at Tabernacle Hill volcano relates to that of other volcanoes in this area in terms of eruptive style, activity and age. Th e volcanoes in this area comprise a large, long lived cluster referred here as the Black Rock volcanic cluster. This cluster has produced bimodal volcanism in this area for more than 2.5 Ma. The Black Rock volcanic cluster is comprise d of at least 30 volcanic centers 17 of which are basalt, 5 are andesite, and 8 are rhyolite in composition ( Figure 1 2 ). The Basin and Range Province of west ern North America contains many monogenetic volcanic fi elds ( Heiken, 1971; Conway et al., 1998; Connor and Conway 2000) however, the Black Rock volcanic cluster in Utah was selected for study for several re asons. First, the last eruption of a volcano in this area was 660 170 years ago (Ice Springs volcano, Figure 1 2 and 4.18 ). Second, there has been a relatively small amount of volcanological work in this area. Aside from several economic viability studies published on Ice Springs volcano (Lynch & Nash, 1980) and several volcanic ash studies (Oviatt and Nash, 1989; White, 1996 and 200 1 ) most of the work published in this are a was aimed at developing a geochemical mod el, the basin's lacustrine activity and sedimentation, or general geology of the area ( Gilbert, 1890; Condie and Barsky,
2 1972; Pushkar and Condie, 1973; Hoover, 1974; Lipman et al., 1978; Evans et al., 1980; Hintze, 1980; Peterson and Nash, 1980; Turley an d Nash, 1980; Nash, 1981; Oviatt, 1989 and 1991; Hintz and Davis, 2003 ) To date much of the physical volcanological and potential volcanic hazards associated with this volcanic cluster has yet to be studied and g iven the recent volcanic activity, an ass essment of the probability of future volcanism and the potential nature of the volcanism appear s to be warranted. The volca noes and volcanic features with in the Black Rock volcanic cluster vary greatly in terms of physical volcanology and composition In particular the interaction between the eruption of Tabernacle Hill volcano and the Pleistocene Lake Bonneville has afforded a well preserved example of the full spectrum of basaltic deposits The deposits range from a variety of phreatomagmatic processes ( Colgate and Sigurgeirsson, 1973; Sheridan and Wohletz, 1983; Wohletz, 1986; Morrissey et al., 2000 ) such as palagonitized tuff and pillow lav as, as well as deposits of lava bombs, inflated p hoehoe flows scoria cones and a partially drained lava lake.
3 Figure 1. 1 : Simplified geologic map of the Black Rock volcanic cluster region of Utah (see Appendix A.5 for large scale version) Only volca nic deposits mountain ranges and undifferentiated lakebed are illustrated here. All faults are normal unless otherwise stated. Map was compiled using 30 x 60 minute geologic maps of Juab, Millard and Beaver counties, 7.5 minute USGS quadrangles, 10 meter DEMs, aerial and satellite photographs.
4 Figure 1 2 (continued) : Legend for geologic map on page 3.
5 1.1 Objectives The objective of this study is to introduce a more detailed evolutionary history for the volcanoes of the Black Rock volcanic cluster based on new interpretations from recent mapping, statistical analysis, geochemical relationships and structural cross sections. As part of this study, a geologic map was produced of the entire study ar ea ( Figure 1 2 ), including many individual volcanic center s (Chapter 4 ) and a comprehensive map of the Tabernacle H ill volcano ( Chapter 2 and Appendices A.1 A.4) D etailed mapping of Tabernacle Hill volcano was used to characterize the stratigraphic and therefore eruptive sequence of the volcano This aided in the enabled development of a more detailed eruptive history for the Tabernacle Hill volcano than previously available (Chapter 2 ). Ballistic ej ecta from the Ta bernacle Hill eruption was also mapped for estimating eruptive velocities trajectories and energy yields (Chapter 3).
6 1.2 Geographical Setting The study area is predominately confined to the Sevier Black Rock and Escalante deserts (north to south, respectively) spanning parts of Millard, Juab, and Beaver counties. The Black Rock volcanic cluster spans 27 7 minute USGS quadrangles, measuring approximately 4,200 square kilometers (Figures 1.1 and 1.2). Included within the field are a are t he towns of Fillmore, Flo well, Meadow, Kanosh, and Delta with most of the undeveloped land managed by the Bureau of Land Management as well as the Clear Lake Wetland Wildlife Management Preserve and the Kanosh Indian Reservation. The major tectoni c features of the area, Basin and Range normal faulting and basin fill sedimentation define the pre volcanic topography of the Black Rock volcanic cluster The Black Rock and Sevier deserts comprise a graben that is bounded on the east by the horst of the Pahvant Mountain Range and to the west by the Cricket Mountains, and is underlain by the Sevier desert detachment fault ( Hintze and Davis 2003). This extensional stress regime has dominated this area for ~ 40 Ma years and continues today ( Thatcher et al., 1999 ; McQuarrie and Wernicke, 2005 ).
7 Figure 1. 3: Shaded topographic relief map of Utah showing the field area (black rectangle), the Black Rock volcanic cluster (red) as well as the major tectonic environments and lakes (blue) Much of the field area consists of lacustrine deposits characterized by fine -grained silts and limestones of the Late Tertiary to Quaternary age that were deposited by Lake Bonneville (Oviatt, 1989; 1991) The average topographic reli ef on the field area is ~ 75 m with t he highest basin-elevation being the volcano Pahvant Butte at 1753 m, or approximately 300 m above the surrounding desert floor (Oviatt and Nash, 1989). The main drainage in the field area is the southwest-flowing Sevier River that flows into the almost dry Sevier Lake (more properly a sink or playa, outside of the western
8 bounds of the study area). Apart from several ephemeral and natural springs, a small wetland area the study area is a dry and poorly vegetated desert The quality of o utcrop exposures in the study area var ies greatly depending on the depositional age of the unit relative to the occupation of Pleistocene Lake Bonneville and subsequently the amount of eolian sand cover. Volcanic deposits that post date o r are synchronous with the Lake Bonneville occupation, such as Pahvant Butte, Ice Springs and Tabernacle Hill, have excellent outcrop exposures, although access is sometimes limited on the more rugged terrains. The older volcanoes that pre date Lake Bonnev ille have been highly eroded and/or partially co vered by the lacustrine deposits Access to the field area is available by a assortment of di rt roads of varying conditions.
9 1.3 Previous Work The USGS geologist G.K. Gilbert (1843 1918) w as the first to describe and interpret the geology and specifically, the volcanism of this area. His initial interpretations and lithographs have remained popular today w ith modern authors due to his keen observations and deep understanding of the dynamic geolog ical processes at work in western Utah Gilbert (1890) correctly surmised the subaqueous nature of several eruptions such as Pahvant Butte and parts of Tabernacle Hill volcano as well as recognizing the youthfulness of the Ice Springs volcano. Nearly a c entury later, Condie and Barsky ( 1972), Pushkar, and Condie (1973) described a b road geochemical survey of seven volcanic centers identifying long term (~ 1 Ma) and short term (0.001 Ma) trends in major element compositions and age relations Their work resulted in a geochemical model to describe the relative parental melts, ascent, and storage of the magmas (see Chapter 4 for further discussion). Hoover (1974) described what he interpreted as the episodic nature of five of the volcanic centers within the Black Rock volcanic cluster. His work concluded that the increase of periodic frequency of eruptions correlates with the increased rate of crustal extension. Oviatt (19 89, 1991) produced two geologic maps of the Quaternary geology of the Sevier and Black Rock deserts. These maps provide an excellent overall context within which to study volcanism in the Black Rock cluster. Oviatt (1991) places emphasis on the eruption of Tabernacle Hill volcano and interprets it to have erupted within Lake Bonneville. Of pa rticular interest in this study is the radiometric age determination (~ 14 Ka) based on
10 tufa deposits found on the Tabern acle Hill lava flow (see Chapter 4 for further discussion). Coincidentally, once the e conomic and geothermal viability of the area had been determined, research interest in the area waned with only several publications focusing on any one of the Black Rock volcanoes since the 1970s ( White, 1996; 2001 )
11 1.4 Overview of Methods Field work for this project was completed during the summer of 2007. The work focused primarily on detailed mapping of the Tabernacle Hill volcano and a brief examination of the other volcanoes in the area. Twelve stratigraphic units were mapped o n aerial photographs of Tabernacle Hill, as well as on a 1:24:000 scale topographic map Using these maps, the a erial extent and volumes of lava flows and pyroclastic deposits were calculated using vector based graphics editing software. The largest of the volcanic ejecta was mapped across the ridge of the Tabernacle Hill tuff cone using a Differential Global Positioning System The ballistic data gathered was then used together with a ballistic traj ectory mod el to estimate the explosivity of the eruption. Lava flow and lava t ube dimensions were also collected on Tabernacle Hill to calculate potential effusion rates and duration estimates. A probabilistic hazard analysis for the entire Black Rock volcanic cluster was statistically modeled based on av ailable radiometric ages for most of the volcanoes within the cluster.
12 Chapter 2 Tabernacle Hill A detailed geologic map is a fundamental practicality to understanding the eruptive history of any volcano. In the peer -reviewed literature, several authors have previously presented sketches and basic geologic maps of the Tabernacle Hill volcano (Gilbert, 1890; Hoover, 1974; Oviatt and Nas h, 1989; Oviatt, 1991) to varying degrees of scrutiny. Hoover (1974) was the fi rst author to make a geologic map that focused solely on Tabernacle Hill and to have explored the physical volcanology and geochemistry of the volcano. Oviatt and Nash (1989) studied the stratigraphic relationships between the ash of Pahvant Butte (see Chapter 4) and Ta bernacle Hill and concluded Tabernacle Hill to be the younger of the two. Oviatt (1991), dated the volcano based on tufa collected in the lava and deduced the volcano to be no older than ~14Ka. Here, new, additional detailed mapping and stratigraphic work was used to refine the geologic map of Tabernac le Hill volcano. The goal of developing a more detailed map was to use this map to develop a more complete interpretation of the eruption, utilizing concepts develo ped in physical volcanology during the last decades (Sohn, 1996; Vespermann and Schmincke, 2000; Valentine et al., 2006; 2007). The mapping defined eight stratigraphic units comprising th e entire eruptive history of Tabernacle Hill volcano on the basi s of physical characte ristics, depositional environments, stratigraphic position, disc ontinuities, and erosional surfaces. The following sections describe each stratigr aphic unit in order of deposition where
13 decipherable. A proposed history of the erupti on sequence is discussed at the end of this chapter.
2.1 Legend of the map and general stratigraphy Geologic maps of Tabernacle Hill vol cano (Figure 2.1A-B; Appendices A.1-A.2) were produced along with a stratigraphic co lumn (Appendix A.4) and several geologic cross-sections (Appendix A.3). The main map produced (Figure 2.1A) predominately features Tabernacle Hill volcano, although the deposits of the neighboring volcanoes Ice Springs, Beaver Ridge I and II appear in the northeastern and southwestern portion of the map. The map covers an area of 35.9 km2 that is predominatel y Quaternary sediments associated with the lacustrine activity of La ke Bonneville during the Late Pleistocene. 14 Figure 2.1: Geologic maps of Tabernacle Hill vo lcano. (A) Full scale version of Tabernacle Hill volcano and associated deposits. A.
15 B. Figure 2.1(continued): (B) Detail of Tabernacle Hill crater. Strikes and dips where measured on stratigraphic surfaces to indicate inferred post-depositional tilting or syndepositional bed forms. The symbol represents a flat lying area where no strike or dip was near horizontal. The dashed line represents a depressed area within the crater floor. The yellow star indicates inferred vent location.
16 2.2 Description of Map Units The Quaternary deposits in the field area are classified on the basis of their lithology, age and environments of deposition as indicated by the map unit symbols. The units were named according to their age (fir st capitalized letter), then by lithology or depositional environment, such as Ptc for Pleistocene tuff cone and Qlf for Quaternary lacustrine fines. The relative ages of the map units are based on radiocarbon ages (where available) from published sources and on st ratigraphic relationships The map units are described in the following in what is believe d to be the correct st ratigraphic sequence, where it is decipherable. Lake Bonneville Deposits (Qlf) Lacustrine sediments related to the occ upation of Lake Bonnev ille are surficially deposited throughout the field area and provi de the foundation on which all Tabernacle Hill deposits sit. These fine-grained sediment s, represented on the map (Figure 2.1A) by Qlf, consist of limestones, fluvial quartzite pe bbles, silts, sands, clays and tufa (Oviatt & Nash, 1989; Oviatt, 1991). Locally, these sediment s are observed to have interacted with the eruptive products of Tabern acle Hill in two areas. Firs t, the deposits of Qlf are observed as cores in accretionary lapilli (Figure 2.6) as loose debris in the bedding layers of the tuff cone (Ptc) and as lithics encased in spatter and in lavas ne ar the central crater. Additionally, Qlf is also be obs erved entrained in the distal edges of the lava flows (Plf) as peperites (White et al., 2000).
Pleistocene Tuff Cone (Ptc) The tuff cone unit represents the lo west mappable stratig raphic unit above Lake Bonneville sediments and has been cons idered by many authors to be the first unit in the stratigraphic succession of the volcano, although there is some evidence of an earlier effusive stage. These phreatic and phreatomagmatic deposits of Tabernacle Hill volcano form the tuff cone, or Ptc as repres ented on the map (Figure 2.1A and B). Figure 2.2 represents a simplified version of Figur e 2.1A illustrating the deposits of the tuff cone. Figure 2.2 : Simplified geologic map of Tabernacle Hill volcano showing the four main outcrops of volcanic tuff (Ptc). 17
18 The volcanic tuff deposits of Tabernacle Hill are exposed in four discontinuous outcrops, though the two largest central outcrops are likely continuous at some depth below the lava flows and exist as one conti nuous tuff cone at the cones very base. The two largest sections are considered in situ and immediately surr ound the central crater area rising to 81.3 m at the highest elevation above the surrounding lake bed (1510 a.s.l.). Although the base of the tuff cone is surrounded by later lava flows, the diameter of the partially covered cone has been estimated to be ~ 2 km. There is little to no evidence of erosion of the tuff cone aside from the mo tion of the lava flows along the base. This deduction is supported by an ab sence of eroded tuff deposits at the base of the cone and other areas where eroded material would likel y collect. Two smaller deposits of the tuff cone were observed at the north and sout h distal edges of th e lava flow and are interpreted to be rafted sections of the orig inal tuff cone (Figure 2.2). While the pieces do not externally exhibit the bedding layers of th e in situ sections, but they do show the same relative proportions of block, bombs, ash and lapilli. The deposits of tuff cone consist of (in order of observed decreasing abundance) volcanic ash, blocks and bomb s, fluvial quartzite pebbles and small blocks, juvenile scoria and accretionary lapil li. Thin beds within the tuff cone vary in degree of induration, with the more indurated layers be ing more coherent, re taining sag and scour features (Figure 2.5A and B). M easurable strikes and dips of these beds range from 12 to 30 and having an average dip of 23 (Figure 2.3). Figure 2.4 shows the expected radial,
outward strike and dip pattern observed with deposits that result from eruption at a single vent. 19 Figure 2.3 : (A)View of the Tabernacle Hill tuff cone (Ptc) looking east across lava flow deposits (Plf). A recent light coating of hail on the volcano shows some of the bedding layers in the tuff cone. (B) Illustration of th e tuff cone to show the depositional units in view.
Figure 2.4: Illustration of the large in situ portion of the tuff cone and locations of strike and dip measurements. 20
21 A B Figure 2.5: (A) Photo showing non-indurated partia lly palagonitized tuff and scour and fill structure. (B) Bedding layers of the lower portion of the tuff cone with a large bomb sag near the upper left corner of the image. (C) Many of the whitish objects seen here are lacustrine lithics that are obs erved throughout the unit. Some of the whiteness is desert caliche, marl and/or tufa. C The main deposit making up the tuff cone is volcanic ash or tuff. The tuff is composed of friable, yellow to greenish-gray, ash that varies in induration and palagonitization. While the tuff is the primary c onstituent of this unit, it is also composed of an appreciable amount of fluvial quartzite as well as other lacustrine/sedimentary lithics. These accidental lithics range from a ngular shards to very rounded pebbles. Many of the lithics observed in the tuff cone have coatings of caliche and tufa. In particular, many of the Type 3 blocks (see description of ballistics below) were observed to have
caliche coatings, while the lakebed-derived rocks such as the quartzite and limestones were mainly observed to have white to gray tufa coatings. The more lithified layers of the tuff cone were also observed to be composed of large accumulations of accretionary lapilli ranging in size from 2 -10 mm. Armored accretionary lapilli were also observed throughout the tuff cone (Figure 2.6). 22 Figure 2.6: Photograph of an armored accretionary la pilli mantled by a very thin coating of desert caliche. The lapilli is cored with a lakebed derived clast then coated with a small amount of basalt. Ballistic Blocks and Bombs The Tabernacle Hill tuff cone (Ptc) is interbedded and covered with numerous blocks and bombs of many sizes and origin s. These blocks and bombs are pyroclasts ejected from the vent during the phreatomagmatic phase of the eruption. The deposition of these blocks and bombs onto the tuff cone caused deformation to the bedding layers such as impact sags (Figure 2.7). Chapter 3 discusses the energies and trajectories experienced by some of the larger blocks. Ma ny of the original bloc ks and bombs erupted
23 during the early phases of the Tabernacle Hi ll eruption were subsequently moved or covered by effusive activity and therefore are only observed on the parts of the tuff cone that were not covered by any lava flow. No blocks or bombs were observed on the lakebed. Due to the steep edge s of the large near-crater pa rt of the tuff cone and the highly disrupted portions of the smaller secti ons of tuff, only a sma ll percentage of the blocks observed were considered to be in situ. The following describes the different types of blocks and bombs observed on Tabernacle Hill volcano. Type 1 Ballistics The blocks and bombs the most abundant on the tuff cone have a juvenile magmatic origin associated with Tabernacle Hill activity. These ballistics are generally spatter agglutinations and mor phologically approach an aerodynamic teardrop appearance (Figure 2.7). The vesiculari ty of these bombs ranges greatly from very small bubble populations (~1%) within the clast to large coalesced bubbles (>20%) that define the shape of the clast. Blocks of this natu re are highly oxidized and microcrystalline, and contain occasional sedimentary xenoliths.
24 Figure 2.7: Photograph from the summit of the tuff cone showing a large Type 1 bomb. Based on deformation of bedding, this block is considered to be in situ but has rotated out of section. Type 2 Ballistics These blocks and bombs constitute the second largest population on the tuff cone (Figure 2.8 and Figure 2.13) These ballistics ar e large juvenile blocks that resemble lavas seen in the lava lake walls (Pll). The blocks range from ~64 mm to several meters in diameter. The te xture is very similar block to block, with vesicularity between 10 and 15% and large (>2 mm) phenocrysts of plagioclase.
25 Figure 2.8: Photograph of a large Type 2 block entr ained in a very indurated section of the tuff cone. Type 3 Ballistic s Less abundant on the tuff cone are light gray blocks derived from the Beaver Ridge andesite fl ow (Figure 2.1). The Beaver Ri dge andesite flow can be seen in the southern portion of the map ar ea (Figure 2.1). It is believed to extend underneath Tabernacle Hill at least as far as the vent, as blocks of flow are found on the tuff cone. These blocks are generally smooth-edged and range in size from several centimeters to > 1 m (Figure 2.9).
26 Figure 2.9: Photograph of two large blocks near the lower portion of the tuff cone. The lighter colored block is a Type 3 blocks from the Beaver Ridg e andesite flow. The darker, more angular block is a Type 2 juvenile block. Note th e rock hammer for scale. Type 4 Ballistics The least abundan t, although still very perv asive throughout the unit, are the very small pebbles and sediments from the lakebed. The largest sized deposits of this group of ballistics mainly fell into tw o groups: very rounded fl uvial quartzite pebbles and angular limestone clasts. They are f ound interbedded throughout the bedding layers and sometimes within the Type 1 and 2 ballistics. The blocks and bombs on Tabernacle H ill occur at distance s from ~250 m to ~400 m from the vent and are useful indicat ors for the explosivity of the eruption.
Pleistocene Lava Lake (Pll) The Tabernacle Hill lava lake deposit s, Pll on the map (Figure 2.1B and Figure 2.10), represent the last cooling surface of a lava lake that has since drained and left a crescent shaped crater near the center of the volcano. The re maining crater has a nearly constant rim elevation of 1425 m a.s.l. and measures ~400 x 800 m and is ~15 m deep. For mapping purposes, the depositional units co mprised of lava, such as the lava lake (Pll), lava flows (Plf), and th e intra-crater deposits, are di stinguished by their depositional processes. For example, the crater rim acts as a geographic boundary regarding the differences between the lava lake unit and the lava flow unit. Figure 2.10: Simplified geologic map of the crater of Tabernacle Hill volcano showing the distribution of lava lake deposits (Pll). 27
The lava lake surface is ge nerally smooth but is broken into large polygonal plates related to cooling and final subsidence of the lake (Figure 2.11). Figure 2.1b shows a dashed line around a slightly depr essed area of the crater floor, possibly an area of drainback. Drain-back is a process in which lava is still fluid enough to flow-back into the vent in response to changes in pressure with in the volcano conduit, once the eruption has either ceased or paused for some period of time. Some areas along the crater walls are mantled by a veneer of lavas with feat ures characteristic of drain-back. 28 Figure 2.11 : Photograph of the Tabernacle Hill crater site of the former lava lake, looking south. The slight depression observed within the crater (dashed line in Figure 2.1B) corresponds with projected dip directions from the strikes and dips measured in the stratified bedding layers of the tuff cone and is the most likely location of the vent. The main significance of this depression is as an or igin point for the ballistics analysis. While
29 the mapped deposits of the Tabernacle Hill lava lake only repres ent the last cooling surface of the lava lake, the st ratigraphic relationships of the intra-lake deposits suggest several filling and draining events an d even several explosive events. Pleistocene Lava Flows (Plf) The Tabernacle Hill lava flows, unit Plf on the map, is actually a combination of several lava flows that overflowed the centr al crater, broke thr ough the confinement of the tuff cone, or broke out of proximal lava tubes (Figure 2.12). However, the boundaries of individual lava flow units were not ab le to be traced over long distances. The Tabernacle Hill lava flow field covers an area of ~18 km2 across the nearly horizontal Lake Bonneville ancient lake bed. Overall, th e lava flows consist en tirely of inflated p hoehoe flows riddled with a complex netw ork of lava tubes (Plt). The average thickness near the central crater is ~ 52 m and tapers to between 3 and 6 m at the flow front. Across the lava flow field, several nort h-south trending highangle faults were observed, as well as hundreds of large tensional cooling cracks. The lava flow field surrounding the tuff cone and crater is exclusively p hoehoe and exhibits many of the common characteristics associated with low visc osity melts such as lava tubes, inflated sheets, tumulus, and ropes.
Figure 2.12 : Simplified geologic map highlighting the subaerial extent of the lava flows (Plf). The lava flow field is characterized by its large circular, almost plateau-like shape across the entire expanse of the field. Indi vidual flows are seve ral hundred meters to kilometers long. Several tumuli fields have congregated to the north and south of the crater while the non-tumulated portion of the flow field is pock-marked by large failed inflationary depression as well as lava tube collapses (Figure 2.13). The tumuli are generally several meters to tens of meters in size and are often slightly elongated with at least one deep crack running the length of its axial plane. The flow field is considered to be a large inflated sheet flow. This implie s sustained input during a long-lived eruption 30
(Hon et al., 1994). There are many areas across th e edifice that that have been uniformly uplifted and are nearly flat, gi ving a plateau-like l ook to the area. These structures have been previously referred to as pressure ridg es (Condie and Barsky, 1972). Due to the compressive implication of pressure ridge it is here more appropriate to follow Walkers (1991) term lava rise. Evidence supp orting the inflation of the lava flow field was also observed at the flow fronts where lake bed sediments were entrained by the advancing flow then uplifted several meters off the lake bed where they remain. In many areas around the distal edges of the lava flows, pillow lava s and Lake Bonneville tufa can be found (Figure 2.14 and Figure 2.15). 31 Figure 2.13: Photograph looking south from the tu ff cone at the block and bomb distribution (mostly Type 2s seen here) and tumuli fields in the background.
32 Figure 2.14: Distal edge of Tabernacle Hill lava flow (Plf) near the south end. Whitishgray layer half way up the flow is th e peperitic tufa of Lake Bonneville. Figure 2.15: (A) Photograph showing peperitic tufa entrained by pillow basalts on the distal edges of the Tabernacle Hill lava fl ow. (B) Photograph showing a close up of a broken basalt pillow. The lengths of the lava flows and the dime nsions of the lava tubes were measured and calculated to make estimations of the e ffusion rate and to determine the necessary length of time over which the eruption took pl ace. One of the two methods employed was Walkers (1973) method that simply relates the relationship between the length of the lava flow to the effusivity. This simple re lationship, he argued, was the primary factor
33 controlling lava flow length, while to pography and viscosity are only secondary. Comparing the longest lava flow front leng th (3.2 km) on Tabernacle Hill (measured here as the distance from the crater to the most dist al point) to the other basalts from Walkers (1973) study, the flows are estimated to have an effusivity between 0.3-10.3 m3s-1. Assuming a constant rate of eruption, the duration of the Tabernacle Hill eruption could have ranged from ~1.5 to 50 years. More recen tly, Kilburn (2000) developed an empirical relationship between lava flow effusivity and maximum potential flow length for a lavas. The relationship Kilbur n identified is predominately based on the mechanical and thermodynamic properties of the flows su rface. This relationship is given by: (2. 1) where Lm is the maximum potential lava flow length, describes the extension before failure (10-3 for chilled crust), S is tensile strength of the crust (107 Pa for chilled crust), is the density of the crust (~2200 km m-3 for 20% vol. vesicles), g is gravitational acceleration (9.8 m s2), k is the thermal diffusivity (4.2 x 10-7 m2 s-1), and Q is the mean volumetric flow rate (m3 s-1). Given the known potential of 3.2 km for a Tabernacle Hill lava flow, solving Eq. 2.1 in terms of Q gives a flow rate of 2.9 m3 s-1. The necessary time required to erupt the 0.47 km3 of Tabernacle Hill, assuming a constant flow rate, is ~5.1 years. It is important to note that both of these methods probably overestimate the volume flux associated with this eruption for two reasons. First, the range estimate given by using the Walker (1973) log-log method probably exceeds the volume flux by an order
34 of magnitude (Harris et al., 2007). Volume fluxes for other volcanoes, such as the ongoing Puu vent eruption at K lauea volcano in Hawaii, are reported to have volumetric flow rates, for inflati ng sheet flows, ranging between 0.2-1.1 m3 s-1 (Hon et al., 1994) and transitions to a flows with flow rates exceeding 5 m3 s-1 (Rowland and Walker, 1990) Likewise, the Kilburn (2000) method also probably overestimates the volumetric flow rate because this method was developed for use with a flows. Because of a p hoehoe flows tendency to spread out in a large sheet in absence of a topographic confinement (in this case ther e is a negligib le slope of 1 ), and insulate itself more efficiently having less surface area than an a flow, as well the propensity to form tubes, it takes less volume flux to drive a p hoehoe flow to the same length as an a flow. Therefore the true effusivity of the Tabe rnacle Hill eruption probably lies between the lower end of the Walker (1973) scale and Kilburns (2000) method (0.3-2.9 m3 s-1). Pleistocene Scoria Cones (Psc) Four physically distinct scoria de posits, Psc on the map (Figure 2.16), were observed on Tabernacle Hill. The largest scoria deposits are two partially destroyed cones on the east crater rim. These cones reach a heig ht of ~60 m above the crater rim (Figure 2.17). The cones each have aprons consisting of large amounts of loose rubble, but their cores consist of agglutinated layers that have been rotate d and undercut by subsequent lava flows, resulting in n ear-vertical and overturned laye rs. Agglutinated porphyritic cinder within these layers ranges from highly vesiculated to denser, fused lapilli-sized fragments. Some scoria layers are so agglutinated there is evidence of rheomorphic flow.
Many xenoliths of Lake Bonneville sediments (Q lf) are entrained within the agglutinated that layers (Figure 2.18), as we ll as blocks and bombs. The la va lake units of the crater wall were observed at several outcrops stratig raphically below the massive portions of the cones, indicating that the c onstruction of the cones was pr eceded by lava lake activity. The sharp contact on the east side of the cone s between cinders and lava, the rotated and overturned layers of agglutinated scoria, and the lack of scoria within the crater indicate that lava lake activity also persisted after the scoria cones were formed. 35 Figure 2.16 : Simplified geologic maps of Tabernacl e Hill highlighting the locations of scoria deposits. The darker shad e of purple indicates the more agglutinated deposits while the lighter purple indicates that the deposit is mainly rubble.
36 Figure 2.17: (A) Photograph looking east at the two large scoria cones on the east rim of the central crater. (B) Illust ration of the scoria cones. The darker purple color on the scoria cones indicates solid st ructures or highly agglutinated layers while the lighter purple indicates loose cinder. Crater rim talus is represented by t. Figure 2.18: Photograph of a sedimentary xenolith (Qlf) encased by oxidized cinder of the scoria cone (Psc).
37 Additional scoria deposits near the south and west crater wall have been subsequently covered by lava flow/lava lake deposits. Another large mass of scoria deposits was found encased in a shell of dense lava beneath a large rheomorphic block in the southern nook of the central crater (Figur e 2.27). This deposit c onsists entirely of loose, unwelded black cinders, and unlike the large cones to the north, does not contain any observable lacustrine xenoliths. Only one other scoria deposit was observed within the crater. On the west side of the crater, a small outcrop of scoria can be seen between two layers of slabby p hoehoe, Pir on the map (Figure 2.16). These cinders characteristically resembled t hose found in the south crater and not those of the two large cones on the east rim. The cinders are l oose, unwelded, black and lacking in the characteristic large xenolith population seen in the two cones. The last observation of scoria was observed at the southern flow front of the lava flow (Figure 2.16 and Figure 2.19). Unlike the other deposits asso ciated with this unit, the scoria in this area is very agglutinated and bright red from oxidation a nd closely resembles the agglutinated layers seen in the crater rim cone s (Figure 2.17 and Figure 2.18), but lacks lacustrine xenoliths.
38 Figure 2.19: Photograph of agglutinated scoria (P sc) observed at the south end of the Tabernacle Hill lava flow (Plf). One small outcrop of scoria deposits th at was not mapped is located on the northnortheast section of the main in situ portion of the tuff cone. A small excavation pit reveals several meters of scoria deposits within the pit. It is unclear whether this deposit underlies the entire tuff cone or if it is just localized here. The deposit may reflect an earlier phase of Strombolian activity.
39 Figure 2.20 : Photographs showing the additional sc oria deposit located within the main in situ section of the tuff cone. Pleistocene lava tubes (Plt) There is an immense network of lava t ubes, Plt on the map (Figure 2.21), present throughout the lava flow field of Tabernacle Hill. The active lava flows were highly channelized and evolved into lava tubes. These lava tubes are pervasive throughout the flow field and range from > 1 m2 to > 90 m2 in cross-sectional area. Their exposures and explorability varies depending on the amount of collapse that has o ccurred (Figure 2.2124). Lava tubes are either exposed well enough to identify the origin al tube wall, floor and/or ceiling, or are collapsed with few or no exposures. The largest explorable tube (Figure 2.23) may have transported lava at a volumetric flux on order ~90 m3s-1, based on the assumption of lava trave ling in the tube at ~1 m s-1 and a 90 m2 cross-sectional area (Walker, 1973).
40 40 Figure 2.21 : Simplified geologic map of Tabern acle Hill volcano highlighting the locations of lava tube collapses. Figure 2.22 : Photograph of the interior of one of many large lava tubes that remain uncollapsed. Ceiling is about 7 m high; note th e remains of camp fire in the foreground.
41 41 Figure 2.23: Photograph looking north at the largest lava tube observed on Tabernacle Hill. Lava tube is approximately 40 m across. Location is just north of the central crater. Fire pit The lava tube network within the lava fl ow field of Tabernacle Hill is extensive, suggesting a prolonged eruption. Th e fact that so much of the original tuff cone and scoria cones are missing and likel y rafted away by lavas suggests that the lava tubes were effective at transporting portions of the cone well away from the vent area, as observed at other numerous small-volume volcanoes (Sum ner, 1998; Valentine et al., 2007). Pleistocene Crater Rim Rubble (Pcr) The western edge of the Tabernacle Hill crater is littered with several long (>100 m) thin deposits (~1 m) of angular, vesicu lated piles of rubble (< 0.5 m). This rubble pile, Pcr on the map (Figure 2.24), occurs onl y around the crater imme diately adjacent to
the outward dipping crater rim. Strikes and dips were taken along the crater rim, and the rubble pile is only observed where the crat er rim is dipping outward (Figure 2.25). Figure 2.24: Simplified geologic map of the crater area of Tabernacle Hill highlighting the locations of the cr ater rim rubble piles. 42
43 Figure 2.25 : Photograph showing the out ward dipping edges of th e southwestern side of the crater rim and adjacent rubble. Note walking stick ~1.5 m for scale. The origin of the crater rim rubble pile is unclear, however, at least 3 theories are proposed: (1) the angular blocks that make up the rubble pile rolled there from a higher elevation of an edifice that was completely destroyed by subs equent lava lake activity; (2) the blocks are small angular pieces of th e cooled surface of the lava lake that was somewhat mobile and pushed itself against the crater wall, crea ting a lava rises (Walker, 1991) like those seen on frozen lakes in the winter; and (3) the tilted surfaces and blocks reflect an period of time in the lava lake when very large (> 5 m) fluid bubbles would form and burst, as sometimes s een on very active flows in Hawaii.
Pleistocene rheomorphic intra-crater deposits (Prc) Two large (>100 m) blocks were mapped in the Tabernacle Hill crater (Figure 2.26). These blocks, Prc on the map, are man tled by extremely thin (~10 cm) and fluid lava flows and peak at higher elevations th an the crater rim, indicating remobilization (Figure 2.27). These rheomorphic intracrater units (Prc) have many unique morphological characteristics such as draperie s and ropes. The units are massive enough to have created a skirt of talu s from their own degradation. Figure 2.26 : Simplified geologic map highlighting the rheomorphic lava lake deposits (Prc). 44
45 Figure 2.27: (A) Photograph showing the features in the southern portion of the central crater. (B) Illustration of the southern portion of the central crater showing the aggregation of deposits. These large intra-crater deposits represen t the incomplete transport and drain-back of the lava lake and lava tubes. The large piece shown in Figure 2.27 was piled on top of a large scoria deposit, and is believed to have stopped as it rafted toward the entrance to a large lava tube in the southern area of the crater. This rafted block of material is inferred to have blocked the lava tube, thus stopping the lava from escaping the crater here and possibly causing it to over flow the crater rim. Pleistocene Intra-crater Rubble (Pir) Similar to the large remobilized blocks of Prc, is the large accumulation of spatter, slag and rubble within the crater Mapped as Pir (Figure 2.28), these large mounds are exclusively found next to the crater wall and are interpreted to be the result of lava lake instability (Stovall, in press ). The mounds are composed of massive layers of unconsolidated cindery rubble, agglutinated spatter layers and other unique lava lake
activity-related features such as the honey-comb feature se en in Figure 2.29. As with Prc, several sections of these mounds are at a higher elevation than that of the surrounding crater rim. The deposits range from highly vesiculated, oxidized to bright red and cindery to small polygonal shelly p hoehoe deposits. Figure 2.28: Simplified geologic map of the crater area of Tabernacle Hill highlighting the various locations of intra-crater rubble pile s. The darker shades of blue indicate solid structures while the lighter colors repr esent rubble derived from the structures. The intra-crater rubble is a term of elimination. No other depositional mechanism was identified that could explain these de posits. These deposits may represent failed crater walls that rotated as they were surrounded by lava, or vents that formed within the 46
lava lake. These deposits do show a similarity to one another in that they are all capped with many small, very fluid flow units with abundant drap eries (Figure 2.29). 47 Figure 2.29: Photographs showing the stacked stru cture of some of the intra-crater rubble as well as the unique honeycom b features found in the crater.
48 2.3 Eruptive History This section develops an eruptive histor y for the Tabernacle Hill volcano based on the observed and inferred relationships between all of the geologic units. The units represented in this discussion do not necessa rily appear throughout the entire volcanic edifice; in fact most units are discontinuous. It should be noted that Tabernacle Hill s age has not very well constrained. The only dating that has been done on Tabernacle Hill was on a piece of tufa recovered from the eastern distal edge of the lava flow (Oviatt, 1991). This date (14,320 320 yrs) is often referred to as the date of the Tabernacle Hill erupti on (Oviatt & Nash, 1989; Oviatt, 1991; Zreda et al., 1991; Cerling and Craig, 1994). However, this date is the age of the tufa and can only be interpreted as an upper bound for the age of Tabernacle Hill, as it was entrained by the advancing lava flows, not accumulated after deposition (Figure 2.31). It is unclear how much interaction with Lake Bonneville occurred, however.
Figure 2.30: Photograph of pillow basalts with tufa deposits between them. Contrary to earlier interpretations (Ovia tt, 1991), I interpret the eruption to have occurred in a wet sub-aerial environment rath er than in a sub-aqueous environment. The central tuff cone of Tabernacle Hill vol cano represents the initial phreatomagmatic stage of a sustained eruption that produced a wide range of volcanic deposits. Two lines of evidence suggest that this early phase of the erupti on, although phreatomagmatic, did not occur through a standing body of water. Firs t, the eruption of Ta bernacle Hill volcano is about 14 ka (Oviatt, 1991) based on radiocarbon age determinations, and therefore occurred near or after Lake Bonneville receded to the Pr ovo shoreline, which was not extensive enough to submerge the volcano (Figure 4.1). Second, the abundance of accidental lithics suggests that the h ydromagmatic fragmentation was driven by groundwater, rather than by inte raction with surfa ce water (Fisher and Schmincke, 1984). 49
50 Evidence also suggests that eruption t ook place after Lake Bonneville regressed below the Provo Shoreline, or at least duri ng a low-stand in oscillation of the Provo shoreline stabilization. The Provo shoreline is estimated to have st abilized at the ~1,450 m a.s.l. elevation subsequent to the B onneville flood around ~14.5 ka (Godsey et al., 2005; OConnor, 1993). However, there are no lakeshores or wave cut facies observed on Tabernacle Hill at or near the 1,450 m level, suggesting that the Tabernacle Hill eruption took place after the lake receded from th e Provo level. Regional mapping of the area places the Provo shoreline at an elevati on of 1,454 m 10 km east of Tabernacle Hill (Hintze and Davis, 2003). It has been suggest ed by Hoover (1974) and Oviatt (1991) that Tabernacle Hill erupted through the waters of Lake Bonneville to produce the tuff cone and that the Provo shoreline exis ts locally on the outer margins of the lava flow field at the ~1,457 m level. Oviatt and Nash (1989) sugg est that the 3 m diffe rence in shorelines is due to either incomplete isostatic rebound or magma chamber subsidence. However, it is not physically possible for th e small volume of basalt (~0.5 km3) erupted from Tabernacle Hill to loca lly load the lithosphere sufficie ntly to produce a 3 m change in topography through isostatic adju stments. Together, the vo lcanological evidence, and lack of shoreline features, so prevalent at the nearby Pahvant Butte (White, 1996; 2001), suggests that Tabernacle Hill erupted through a wet, perhaps marshy, sub-aerial landscape. A few isolated basalt pillows are found on the margins of the lava flow field (Figure 2.14) and these have been used to s uggest a sub-aqueous er uption of Tabernacle Hill (Batiza and White, 2000). A lthough rare on the lava flows or at the lava flow margins, these pillows are clear evidence of interaction with water. An alternative
51 interpretation, explaining the occurrence of pillows in isolated areas but the general lack of pillows over the vast majority of the lava flows is there was sufficient water available to form pillows in isolated areas, such as where lavas flowed into surface ponds. At the time of the lava flow eruptions, recent regressi on of the lake and Late Pleistocene climate change provided just such a marsh-like e nvironment. Pillows may have also formed where lavas reached snow/ice-fields, which were common in this area during the Late Pleistocene, and which again would provide su fficient water to form pillows in localized areas of the flow (Wilch and McIntosh, 2007). The initial eruption of Tabernacle Hill commenced as lava rose through the upper crust and violently interacted with surface a nd/or near-surface water, resulting in the formation of the tuff cone. The combinati on of increased eruption rate of degassed magma and drying out of rocks surrounding the volcano conduit led to a change in eruptive style. Effusive lava pooled in the crater created by the e xplosive eruptions and the newly formed tuff cone. Continued effusi ve eruption resulted in failure of the tuff cone walls, probably to the north-west and th en the southern portion of the tuff cone. These breaches allowed lava to spill out onto the basin floor, forming the flow field, which is remarkably symmetric due to the flatness of the topography.
Figure 2.31: Inferred cross section through Tabern acle Hill corresponding to lines A and B in Appendix A.1. The lava lake of Tabernacle Hill repres ents the changing eruptive style of the eruption. It is unclear from th e field observations if the change in eruptive style was gradual or abrupt or if ther e was a hiatus between formation of the tuff cone and lava effusion. One possible explanation for the change from an explosive to effusive eruptive style is that the water that was initially pr esent to cause fragmentation and build the tuff cone was dried out of the area by the heat of the rising magma. This implies that the flow rate of water toward the volcano is low compar ed to the rate at which this water can be 52 vaporized, again implying a sub-aerial erup tion. Once the eruption became effusive, it
53 he y shows e Figure 2.32: Photograph showing the northern rh eomorphic piece of tuff cone. The deposit lies directly next to a large normal fault which affords a view of the underlying The scoria cone deposits of Tabernacle Hi ll are key indicators that the eruption did not simply settle down to an effusive state. Clearly, at some point after the lava lake began to fill the topographically confined crater carved out by the vent and built up by t tuff cone. Eventually the volume of the lava lake over-pressured the walls of the tuff cone and it overflowed, taking large portions of the tuff cone with it (Figure 2.2). The lava lake may have overflowed any number of times, but at least two locations for the overflow are evident, the large breach to the northwest and the smaller breach to the south. It should be noted that previous authors (Hoover, 1974; Oviatt, 1991) have interpreted these transported sections or rafts of tuff cone to be addition vents. Figure 2.32 clearl the northern rafted tuff cone s ituated directly on t op of the massive lava flow that has been cut by a normal fault. No evidence sugge sts the presence of an additional eruptiv vent in this area. layers. View is looking east at the scarp of the footwall, offset is approximately 5 m.
54 had coo ed at the tubes were proba bly a main mechanism of transport for the lava. D f tive led and built flow units, the eruption style changed to a more Strombolian eruptive regime. This was probably marked by fire-fountaining and explosions. Because four different scoria deposits observed on Tabernacle Hill appear dissimilar in their morphology and textures, they likely repres ent an alternation between effusive and explosive eruptions. The existence of large lava tubes indicates that the lava flowed for an extend amount of time and th uring this time, the lava lake probabl y continued to fluctuat e resulting in many o the intra-crater features such as the large rheomorphic blocks (Prc). Particularly, the features clustered in the southern region of the crater app ear to have blocked a major tube, possibly resulting in the overflow at to the south. Also during this time, the erup regime appears to have had episodic explos ive eruptions that created two large scoria cones and numerous other scoria deposits throughout the crater and at least one that was transported to the southern distal edge of th e lava flow front. Finally, at the end of the eruption the vent must have remained suffici ently unblocked to allow the nearly complete drain-back of whatever residual mo lten lava remained in the crater.
Chapter 3 Ballistic Analysis Detailed descriptions of the setting, ge neral geology and se quence of eruptive events of the Tabernacle Hill eruption are give n in Chapter 2. This chapter highlights one component of the composite proximal pyrocla stic deposits produced during the initial phases of the Tabernacle Hill eruption. The gove rning equations, trajectories and energies associated with the volcanic blocks erupted and emplaced on the tuff cone during this phase of the eruption are described and analyzed. During the initial phreatomagmatic erupt ive phase, magma ascended through the relatively thick (30-34 km) crust, perhaps from a reservoir as deep as 15-35 km (Condie and Barsky, 1972) and interacted explosiv ely with the near-surface water and atmosphere. The resulting rapid vapor expans ion and magmatic fragmentation forced a variety of pre-existing sedimentary and igneous rocks to violently erode and mix with the ascending magma, thus creating the wide vari ety of volcanic blocks and bombs observed on Tabernacle Hill volcano. Continuing phreatomagmatic explosions ul timately produced a low rim of ejecta (~150 m high) in a circular pattern around the or iginal vent in the form of a tuff cone (Appendix A.2-3). Later, a change in the eruptive style from e xplosive to effusive either buried or carried away blocks or bombs that may have extended beyond the present exposure of the tuff cone, thus restricting the range at which blocks can be observed. Blocks and bombs were not observed on the lakebed deposits beyond th e distal edges of 55
the lava flows and this is likely due to the f act that they were not ejected that far. I assume the maximum lateral extent travelled by the blocks during ba llistic transport is somewhere beyond the distal edge of the tuff c one, but less than the distal edges of the lava flows. Due to these uncertainties, as well as uncertainties associated with the initial velocity and eruption angle, the following cal culations should be regarded as a minimum estimate of Tabernacle Hills explosive energy. 56
3.1 Background and Previous Works The study of ballistics in volcanology serv es to aid understanding of the dynamic nature of explosive eruptions, including block trajectories, eruptive energies, gas-rock mass fractions, explosion and fragmentati on depths and conduit geometries. Early ballistic studies of volcanic phenomena were derived from military studies of short and long-range missile trajectories. Early observers, such as Minakami (1942), were able to recognize the mathematical relationship betw een muzzle velocity and ejection angle. Wilson (1972) was one of the first Earth scie ntists to develop an algorithm from the equations of motion of a ballistic trajectory th at also accounted for air resistance or drag. Because of the large ambigu ity in determining unique solutions for the eruptive velocities, the ballistics of many volcanoes are unstudied. However, recent software improvements have made the problem of calculating ballistic trajectories more approachable. Mastin (2001) wrote A Simple Calculator of Ballistic Trajectories for Blocks Ejected During Volcanic Eruptions. Known more commonly as Eject!, his simple numerical calculator can estimate the range of a block based on a variety of input parameters such as block size, initial velocit y, angle, elevation, and zone of reduced drag. I have developed a simplified version of Eject for analytical analysis and compared the results to Eject! 57
3.2 Sampling and Characterization Direct observational measurements of ballistic velocities and trajectories are rare. More common, and more readily available for study, are the observations that can be made of subaerial distributions of ballis tically transported blocks. The two most important measurements that can be made in the field are clast distribution and size (Wilson, 1972). The dimensions and distance of a block from the vent can be used to compute theoretical ranges based on assumptions of initial velocities and ejection angles. The observational range can then be compared with the theoretical range to determine likely scenarios for the eruptive ve locities and angles (Wilson 1972). Field work done between May and June 2007 yielded a comprehensive sampling and analysis of the largest (> 0.04 m3) in situ basaltic blocks on the rim of the Tabernacle Hill tuff cone (Figure 3.1). Blocks and bombs found elsewhere on Tabernacle Hill volcano were not mapped for two reasons. First, many blocks and bombs that were originally deposited inside and outside the tuff cone have been removed or otherwise displaced by the subsequent effusive and explosive pha ses of the eruption. Second, the remaining blocks on the tuff cone, both on the inner a nd outer slopes, may have rolled down the flanks of the cone to their current positions. Calculations pe rformed on blocks in either scenario would result in unde r-and-over estimates of mu zzle velocity (Figure 3.2). 58
Figure 3.1: Shaded relief map illustrating Tabernacle Hills tuff cone (Ptc) and showing the locations of the 74 blocks measured (red circles) and mapped for this study. Accordingly, 74 blocks (Figure 3.1), ranging in size from 0.2 to 1.6 m in diameter were measured along a ~650 meter long circular transect around the proximal crater area on the summit ridge of the tuff cone (Figur e 3.3 and Figure 3.4). The blocks are only observed on the tuff cone itself (both the in situ tuff and the rafted pieces). Blocks were measured to have a maximum distance of 411 m from the vent, although, almost certainly, many blocks were ejected further but have since been covered by lava flows. The block locations were determined usi ng a differential Leica GS20 single frequency Global Positioning System. The blocks were assigned a number, measured along their 59
three orthogonal axes and described in terms of physical characteristics, including shape, composition and vesicularity. The point of origin for the rocks was assu med based on the previous observation that a circular depressed area of the crater fl oor (Figure 2.1) was an area of possible drainback for lava and therefore the best possibl e choice for a point of origin (see Chapter 2 for a further explanati on of this assumption). Figure 3.2: View of Tabernacle Hill tuff cone l ooking north-northeast at the inner flank of the tuff cone. Arrow points to blocks that were not measured because they probably rolled to their curren t location. (Stark contrast in vege tation is due to the Great Millard Co. fire that burned parts of the tuff cone in July 2007. The small dirt road below the rim of the tuff cone was enough to act as a barrier for the fire). 60
Figure 3.3: Image of an in situ block on top of the Tabernacle Hill tuff cone looking west-southwest. Block is cemented in partially palagonitized tuff. Figure 3.4: Large Type 1 block on the rim of Tabernacle Hill tuff cone looking north. This block produced a large sag structure, not especially visible in this photo (note Ice Springs volcano to the left in the background). The ballistic analysis described in the following was developed using the equations described in Wilson (1972), Self et al. (1980) and Mastin (2001). 61
3.3 Analysis As blocks are ejected from a volcanic vent they follow a parabolic path through the atmosphere. Aerodynamically, the blocks conserve momentum but are acted on by external forces such as drag, gravity, wind, a nd to a negligible exte nt, the motion of the Earth. As the initial velocity of the block d ecreases, drag and gravity cause the block to fall. These motions and forces are theoreti cally described in the following for the 74 blocks that were measur ed at Tabernacle Hill. This analysis uses a simple model for th e motion and trajectories of the blocks measured on Tabernacle Hill. The model wa s run on every block for the conditions of constant air drag and no drag; it was then co mpared with Mastins Eject! program under the same conditions (Figure 3.9). Eject! is a simple numerical forward calcu lator for determining the distance and other trajectory-related variab les of a block based on input parameters such as initial velocity and angle. This model was develope d to run inversely to determine the initial velocities and angles of a block given its di stance and size. This model was created to show the possible ranges in initial velocity by changing the eruption angle based on the analytical and numerical equa tions from Self et al. ( 1980) and Mastin (2001). The program was then designed to calculate the f light paths of each bloc k with four initial angles; 25, 45, 65, and 85. 62
3.3.1 Methods In the following analysis, several assumptions and simplifications were made due to a lack of direct observational data. The trajectories of the blocks were modeled assuming no wind, as no wind data were available for this eruption. However, the asymmetrical shape of the tuff cone height does suggest a northeast wind direction. The Coriolis force, or Coriolis Effect, is simply the effect of the Earths rotation on l ong range ballistics and likely has negligible effects on the Tabernacle Hill blocks and is therefore not included in the model. The Magnus force, also known as spin drift, is the force associated with block rotation and can act to stabilize or destabilize a ballistic duri ng its flight (Mastin, 2001). The Magnus force is not included here. Th e motion of the blocks at the moment of ejection from the vent or vent area is very chaotic, with the blocks not stabilizing until the latter part of their flight, if at all, and therefore this m odel assumes the blocks leave the vent in a stable configuration. The analysis was performed under conditions of a constant drag and no drag for simplicity. The analysis di d not include a zone of reduced drag near the vent (see below for further discussion of drag conditions). The blocks measured on the rim of the tuff cone of Tabernacle Hill have irregular but equant, blocky shapes. For ease of calculations, after the blocks were meas ured in the field, furt her calculations were made by estimating the block shapes to be an average between a cube and sphere. Representative ejection angles of 25, 45, 65 and 85 were chosen for analysis that required angle comparisons; however, the angle of 45 (being the most efficient use of kinetic energy) is subsequently us ed for all numeric al analysis. 63
3.3.2 Governing Equations As blocks are ejected into the atmosphere from a volcanic vent they are immediately acted on by the forces of drag and gravity, which in turn affect the acceleration and deceleration of the block in the horizontal ( x ) and vertical ( z ) directions (Figure 3.4). The components of these forces are; (3.1) (3.2) where Fx and Fz are the horizontal a nd vertical components of a blocks motion, respectively. The right-hand te rm in Equation 3.1 represents the force per unit mass of drag in the horizontal direction, where vi is magnitude of the initial velocity vector, a is the density of air (1.013 x 105 Pa a.s.l.), r is the density of the block (2500 kg/m3), A is the cross-sectiona l area of a block, Cd is the drag coefficient, m is the mass of the block and g is the acceleration due to gravity (9.8 ms-1). Because Equation 3.2 represents the forces in the vertical direction, it contains the magnitude of th e drag force vector as well as the gravitational force per unit mass v ector (Self et al., 1980; Mastin 2001). The following equations are used to determine effects of different drag coefficients on the flight path as well as initial conditions of the observed blocks. The analysis considers 64
the cases of zero drag, constant drag and vari able drag. The program Eject! was then used to compare some of the numerical analyses. The drag coefficient is a dimensionless qua ntity used in the drag equation (Equation 3.3) that describes the amount of aerodynamic dr ag caused by fluid flow, in this case a large basaltic block through the fluid of ai r. While in flight, the drag coefficient constantly re-adjusts for the changing density of air (i.e. as the bl ock is propelled higher into the atmosphere the air is less dense and therefore creates less friction with the block, and as it descends back into denser air th e drag increases again). The drag equation is used to calculate the force of drag experienced by an object due to a fluid through which it was moving: (3.3) where Fd is the force of drag, is the density of air, v is the velocity of the object relative to air, A is the reference area and Cd is the drag coefficient. The simplest way to calculat e a projectiles trajectory or initial velocity is to assume that it is erupted into a vacuum, in which there is no frictional resistance from the atmosphere. These calculations can be easily don e in the field and are therefore estimates. By not accounting for any drag, the following eq uations result in a slight underestimate of velocities that increase as the block size decreases. However, in such a situation the required equations can be obtained by simplifying Equations 3.1 and 3.2 to: (3.4) (3.5) 65
The position of a block at any given time is then calculated by integrating Equations 3.3 and 3.4 twice with resp ect to time to give (3.6) (3.7) where x(t) is the horizontal component of the velocity magnitude vector, z(t) is the vertical component of the velocity magnitude vector, vi is the initial velocity, is the ejection angle, g is gravity and t is time. To determine the final range of the block ( xf): (3.8) Figure 3.5: The relationship between all 74 measured blocks on Tabernacle Hill and initial velocity ( vi), range ( xf), block size and eruptive angles for the condition of zero drag. Bubble size corresponds to th e relative volume of each block. 49 51 53 55 57 59 61 63 65 245 265 285 305 325 345 365 385 405 425Initial velocity (Vi)Range (Xf) 66
Solutions for conditions of constant dr ag have been modeled by several authors such as Self et al. (1980) a nd Mastin (2001). Mastin (2001) explains that to integrate Equations 3.1 and 3.2 for constant drag conditions you must replace from Equation 3.1 must be replaced with and replace from Equation 3.2 with The resulting equations are: (3.9) (3.10) The blocks final ranges were calculated by integra ting Equation 3.8 twice with respect to time to obtain: (3.11) where: (3.12) First the time of flight (tT) is calculated by evaluating Equation 3.16 first from the initial point of the vertical (Equa tion 3.13) to the top of the tr ajectory (Equation 3.14), then integrating again from the top of the trajec tory (Equation 3.14) to the bottom or landing elevation (Equation 3.15): (3.13) (3.14) 67
(3.15) To give: (3.16) Where e is the change in elevation from the vent to the landing point. Conditions of variable drag and changing air density were only calculated using Eject! The program Eject! uses a fourth-order Runge-Kutta numerical method to integrate Equations 3.1 and 3.2 throughout the entire tr ajectory of the block with calculation ending when the vertical position ( z ) of the block reaches the pre-defined landing elevation ( zf) (Self et al., 1980; Mastin, 2001). Th e results of this calculation are compared with initial velocity es timates ran in Eject! (Figure 3.9). A numerical solution to the above gove rning equations using a fourth-order Runge-Kutta method has also been used by Wilson (1972) and Self et al. (1980). The independently derived equations differ sli ghtly; however, the equations derived by Mastin (2000) were chosen for ease of compar ison later with a minor adjustment made to account for the elevation change of the blocks. Although several assumptions were made to determine the ranges of initial velocities of Tabernac le Hill ballistics (eru ptive angle, wind, drag, etc.) these values could be plugged into an energy equation of Self et al. (1980) to gi ve an estimate of the amount of energy involved in the erupti on of Tabernacle Hill. The equation is 68
(3.17) where, xf is the distance of the block from the vent, r is the density of the rock (2500 kg m-3), w is the depth of explosion (assumed here to be ~15 m), g is the acceleration due to gravity, and is the eruption angle. 69
3.4 Results 3.4.1 Drag Comparison In this section I present a graphical representation of the results from equations 3.1-3.16 (see Appendix A.10 for data). First, is the comparison of drag coefficients for the Tabernacle Hill blocks. Equation 3.10 was used on a medium sized block (Block 64) to calculate the analytical relationship between range ( xf) and initial velocity ( vi) for several drag conditions at the erupted angle of 45 (Figure 3.6). The calculation was performed for velocities between 0 and 65 m s-1. At this point the result is purely analytical, however, the observed range ( xf) of 398.8 m is known (re presented by vertical red line on Figure 3.5. The graph illustrates that as the drag is increased from 0 to 1, a higher velocity is needed to propel a rock the same dist ance. An increase from 62 m s-1 for a drag coefficient of zero to more than 72 m s-1 for a drag coefficient of 1 is seen, although because of the large size of the rock (1.23 m in diameter), the drag force is negligible therefore the more appr opriate number is closer to 62 m s-1. The same block velocities were calculated using Eject! Under variable drag conditions, a more realistic approach, and resulted in a initial velocity of 62.9 m s-1 which is almost equal to a zero drag result. It should also be noted that drag force becomes more prevalent the further the block is launched from the vent Likewise, closer to the vent the drag force makes almost no difference, lending little difference between calculations made with a zone of reduced drag and without. 70
Figure 3.6: Effect of several drag coefficients on initial velocity and range for a 1.23 m diameter basaltic block ejected at 45 based on Equations 3.10 and 3.15for Block 64. 71
3.4.2 Analytical The following are results for the analytical analyses performed on the blocks of Tabernacle Hill. Four representative blocks were chosen, the smallest (Block 38), the largest (Block 63) and two random blocks in the middle (Block 1 and 64). The following four graphs represent the graphical relationship between range ( xf) and initial velocity ( vi) based on the representative eruptive angles of 25 45 65 and 85 Figure 3.7 : Graphical representation to the analy tical solutions from equations 3.11 and 3.16 for four blocks at ejection angles of 25 (dark red line), 45 (yellow line), 65 (green line) and 85 (purple line). Vert ical red line represents the observed range from the vent for each block. 72
Table 3.1: Initial velocity results for analytical solutions for several representative blocks on Tabernacle Hill evaluated from Figure 3.8 using Equations 3.11 and 3.16. 25456585 Block 1 6364.577.5170 Block 38 71.573.2583.5192.25 Block 63 6566.482.4189.5 Block 64 69.170.986186 Figure 3.7 shows that the velo city ranges from 63 m s-1 to more than 192.25 m s-1 from the smallest block at the lowest angle to the largest block at the highest angle. As expected there is a gradual increase in initial velocities required to move the respective blocks to the necessary distance with the ve locities increasing rapi dly at higher angles. Somewhat paradoxically, it requires more ener gy to move the smaller blocks to the required distance than the larg er blocks. This is attribut ed to drag having a more noticeable effect on smaller blocks than larger ones (Figure 3.5). 73
3.4.3 Numerical At the moment of ejection from the vent, a block is inclined at some angle, so the initial velocity can be resolved into a vertical and horizonta l component. Since the horizontal equation includes aerodynamic dra g, the vertical component will first be considered in order to develop the eq uations for the horizontal component. Horizontal Components: (3.18) (3.19) Vertical Components: (3.20) (3.21) Time of Flight: (3. 22) where xf is the calculated range for the block, t is the total flight time, vi(x) and vi(z) are the magnitude of the initial velocity in the horiz ontal and vertical dir ections, respectively, and g is the acceleration due to gravity. 74
Figure 3.8: Block flight trajectories for Blocks 1, 38, 63 and 64. Trajectories are shown for angles 25 (yellow line), 45 (green line) 65 (blue line) and 85 (purple line). The graphs illustrate the effective range for each bl ock as well as the vertic al offset from vent to landing elevation. Table 3.2: Results for numeral solutions for four bl ocks erupted at four different ejection angles, where; vi is initial velocity, t is total time of flight and E is the maximum elevation achieved by the blocks. Vi (m/s)t (s)E (m)Vi (m/s)t (s)E (m)Vi (m/s)t (s)E (m)Vi (m/s)t (s)E (m)Block 169.55.344.0158.9888.566.211.95183.65137.527.85957.274Block 3867.146.8557.4764.58.7599.5971.313.1213.5149.941530.41138.35Block 6366.446.7556.361.838.9297.5270.6413.07209.11148.3730.161114.61Block 6482.35.3561.766.58.5112.8173.512.85226.39150.830.351151.42 25 45 65 85 The graphs of Figure 3.9 and data of Table 3.2 illustrate the possible trajectories of a representative sample of blocks from Tabernacle Hill based on initial velocities from Equations 3.10 and 3.15. Velocity estimates range from 58 m s-1 to more than 150 m s-1, 75
based on the four eruptive angles chosen, though the 45 angle represents the most efficient angle at which to transport the blocks and thus represents the minimum velocity estimates. Several representative blocks were chos en for comparison to results from Eject! Again, the blocks represent the largest (Block 38), smallest (Block 64) and two average sized blocks (Blocks 1 and 63) from the popul ation sampled. The blocks were compared under the conditions of no drag and variable drag. Figure 3.9 : Graphical results for calc ulated range of several blocks under the conditions of zero drag (solid blue line = this report dashed red line = Eject!) and variable drag conditions using Eject! (dashed green line) erupted at an angle of 45. Graphs illustrate the blocks respective ranges as well as elevation change. 0 10 20 30 40 50 60 70 80 90 100 110 120 050100150200250300350400450Elevation (m)Range, in meters (x ) Cd0 Eject, Cd0 Eject, Cdvariable Block 38 0 10 20 30 40 50 60 70 80 90 100 110 120 050100150200250300350400450Elevation, in meters (Z)Range, in meters (Xf)Block 64 Cd0 Eject!, Cd0 Eject, CdVariable 0 10 20 30 40 50 60 70 80 90 100 110 120 050100150200250300350400450Elevation, in meters (z)Range, in meters (xf) Cd0 Eject, Cd0 Eject, Cdvariable Block63 0 10 20 30 40 50 60 70 80 90 100 110 120 050100150200250300350400450Elevation, in meters (z)Range, in meters (xf)Block 01 Cd0 Eject!, Cd0 Eject!, Cdvariable 76
Table 3.3: Data from Figure 3.10. where vi is the initial velocity, xf is the computed range, t is the total travel time of the block, and E is the maximum elevation achieved during the flight. Eject!1 uses a zero drag condition and Eject!2 uses a variable drag condition. here Eject!1Eject!2here Eject!1Eject!2here Eject!1Eject!2here Eject!1Eject!2Block 1 58.958.958.9333.189334.433088888.5002688.587.9 Block 38 64.564.564.5399.074399380.68.758.78.6106.1288106.1103.4 Block 63 65.565.565.5391.366389.7384.98.458.48.4109.4419109.4108.7 Block 64 66.566.566.5399.692398.339184.108.40.20612.8125112.8111.9 Xf (m) Vi (m/s) t (s) E (m) 77
78 3.5 Discussion The eruption of Tabernacle Hill resulted in the crea tion of a small-volume (0.47 km3) monogenetic edifice. The initial eruption is inferred to be the most explosive and thus possessing the most energy. This chapter hi ghlights the velocities associated with the erupted energy required to eject large basal tic blocks on or around the proximal volcanic edifice. Ejection velocities were de termined to range between 60-150 m s-1 as a minimum velocity estimate, but were most likely between 60-70 m s-1. These velocities are comparable to the calculations made by Se lf et al. (1980) for Ukinrek Maars. This analysis also illustrates that there is a general sorting of the blocks observed (Figure 3.5). Block size increases with distance away from the vent illustrating that drag is not significant for large blocks travelling short distances. Fagents and Wilson (1993) also showed this on their re-a ssessment of the Ukinrek Maars 1977 eruption. The energy calculation was shown to be ex tremely sensitive to the depth of explosion, which was poorly constrained for this eruption. The resulting approxi mation of a 15 m depth of explosion gives an average of 4.5 x 1011 J or roughly 0.4 kT yield for an eruption angle of 45. Increasing the depth of explosion to 20 m gives an average of 1.05 x 1012 J or roughly 1.1 kT yield. Alternatively, the Ukinre k Maar eruptions of 1977 were estimated to have an explosive power of ~ 2.2 kT yi eld explosion (Self et al., 1980). This is expected since a maar eruption requires far more mechanical energy than a tuff cone eruption (Wohletz and Sheridan, 1983). For a relative energy yield comparison, the atomic bomb dropped on Hiroshima had roughly a 15 kT yield.
80 Chapter 4 Black Rock Volcanic Cluster 4.1 Summary of Volcanism in the Black Rock Volcanic Cluster The eruption of Tabernacle Hill volcano is one of the more recent eruptions in a long succession of volcanism that has been activ e in this area of west-central Utah for more than 9 Ma. The Black Rock Volcanic Cluster (BRVC) cont ains a succession of volcanic activity that is largely confined to the topographic basi n between the Pahvant mountain range to the east a nd the Cricket Mountai n range to the west, although some of the older volcanic deposits de viate into higher topography to the south (Figure 4.1). All of the deposits are volcanic with no known exposur es of dikes, sills, or plutonic bodies. This is attributed to domination of extensi onal tectonics in this area and the resulting sediment flux from the neighbori ng fault-bounded mountain ranges. There are more than 30 volcanoes or vol canic events in the BRVC, 28 of which have had radiometric or radiocarbon dati ng performed on them. Compositionally the cluster consists of 17 basalts, 5 basaltic-andesites, and 8 rhyolite volcanic centers (Appendix A.11) with volumes ranging from 0.01 km3 to more than 85 km3 (Appendix A.6). The following summaries and analysis are based on previously published works primarily focused on geochemistry, radiometri c and radiocarbon dates. It should be noted that much of the literature regarding these deposits are brief Department of Energy geochemical analysis reports carried out in the late 1970s to early 1980s to find viable
81 economic value or geothermal resources in the area and have rather large errors associated with them (Figures 4.2 and 4.3).
Figure 4.1: Simplified geologic location map of the BRVC and surrounding features, based on 10-meter digital elevation data, aerial and satellite photogra phs and the maps of Hintze (2003). See Appendix A.5 for a high-resolution version of this map. 82
Figure 4.1 (continued): Legend for geologic map on page 82. 83 Examination of the temporal occurren ce of volcanism within the BRVC shows that the rate of volcanism has increased over time. This implies that the volcanism experienced by this area may be attributed to a true increase, or waxing of activity, a increased portion of a larger volcanic cycle or simply the understatement of past activity due to the depositional environment. The overall annual recurrence rate (Equation 4.1) for the entire BRVC is shown to be 3.2 x 10-6 events yr-1. (4.1) Where t is the average recurrence rate, N is the number of volcanic events in the time frame of interest, t0 is the age of the oldest event and ty is the age of the youngest event.
84 Figure 4.2 : Cumulative event curve plot for th e BRVC based on data in Appendix A.6. Plot represents the collective volcanic activ ity over time with published dating errors. Basaltic events are shown as red diamonds andesitic as pink diamonds and rhyolitic events are white diamonds. 0 5 10 15 20 25 30 012345678910Cumulative Volcanic EventsAge (Ma) Miocene Pliocene
0 5 10 15 20 25 30 -1012345678910Cumulative Volcanic EventsAge (Ma) Figure 4.3 : Graphical illustration of the cumulativ e volcanic vents and relative area over time. See Figure 4.2 and Appendix A.6 for erro rs associated with age determinations. 85
86 Whether the increased activity represente d in Figure 4.2 reflects a true increase in activity, a small portion of a large volcanic cy cle or the under-recording of older events, the assumption is made here that the volcanis m occurred in three major episodes that are separated by their order of magnitude rate increases. Re call that the recurrence rate for the entire BRVC is 3.2 x 10-6; however breaking the cluster into perceived episodes of changing rates shows an increase by two or ders of magnitude (Connor and Hill, 1995). Figure 4.2 graphically illustrate s that the rates of volcanic activity in the BRVC have increased since ~1.5 Ma and applying Equati on 4.1 shows the recurrence rates before ~1.5 Ma are 1.4 x 10-6 events yr-1, but after ~1.5 Ma increase to 1.2 x 10-5 events yr-1. Further examination of Figure 4.2 shows that there is an arguab le increase just since the last four eruptions, giving th em a recurrence rate of 1.2 x 10-4 events yr-1. This method is somewhat arbitrary and any further geoc hemical and/or radiometric work may significantly impact the boundaries for which these episodes are divided or completely negate them altogether. Spatially the episodes are represented in Figure 4.4, though no clear pattern is relatively discernable, it is conceivable that the most recent volcanism has a locus.
87 Figure 4.4 : Simplified geologic maps of the Black Rock volcanic cluster. (A) Episode I deposits; ~9.1-2.11 Ma. (B) Episode II deposits; ~1.5-0.154 Ma. (C) Episode III deposits; ~31,500-660 yrs. A B C Episode I (9.1 Ma ~1.5 Ma) The earliest deposits of volcanism in th e BRVC are observed in the southern-most region of the area with the rhyolitic eruption of Gillies Hill approximately 9.1 0.2 Ma (Evans et al., 1980; Figure 4.1; Appendix A.6). The volcanism created a cluster of small rounded hills through a series of lava flows, do mes, and some pyroclastic rocks (Evans et al., 1982). Following the initial rhyolitic erup tions of Gillies Hill there was possibly a
88 long pause in volcanic activity (~>3 Ma) in th e area. The lack of volcanism during this time period may actually reflect a long cessati on in activity or under recording due to sediment influx within the basin. The next instance of volcanism recorded was a very small-volume rhyolite flow at Fumarole Butte mapped near the extreme north end of the field (Peterson and Nash, 1980). Several smallvolume, bimodal eruptions persisted in the northern end of the cluster until volcanism once again became more prevalent in the south with the rhyodacitic eruption of Coyote Hills at 2.7 .1Ma (Evans et al., 1980). Following the Coyote Hills eruption, volcan ism began to focus in this area and appears to have a somewhat steady-state o ccurrence over the next six eruptions spanning ~0.5 Ma. The 11 eruptions that make up this episode of volcanism in the BRVC represent the oldest and least exposed of the volcanic events in the area. The occupation of Lake Bonneville as well as a steady influx of sedime nt supply has masked much of the lateral extent of these deposits, which are probably much more extensive than currently mapped and therefore current area and volume cal culations of these deposits are likely underestimated. Some volcanoes from this pe riod may even be completely buried like those in Southwestern Nevada Volc anic Field (Perry et al., 2005). Episode II (~1.5 Ma to ~ 15 Ka) Episode II volcanism began in the cent ral area of the mapped region with the eruption of the Beaver Ridge andesite flow ( Figure 4. 5) after a hiatus of ~0.6 Ma. This episode of volcanism is believed to represen t a sharp increase in eruptive frequency for the BRVC, having produced over 15 eruptions in just over a million years. It should be noted that some of the radiometric dates ava ilable have extraordinarily large errors (i.e.
89 Deseret volcano is 0.4 0.4 Ma) associated with them and ma y not reflect the true time frame of eruption. The Beaver Ridge comple x is located immediately southwest of Tabernacle Hill volcano ( Figure 4. 17) and represents the combination of at least three separate events, although no individual vent s are mapped. The volcanism associated with the Beaver Ridge eruptions would last fr om approximately 1.5 Ma to 0.5 Ma (Hoover, 1974; Best et al., 1980; Nash, 1986). Th e lavas cover approximately 20 km2 and are probably much more extensive than their present outcrop due to local deposition. The Beaver Ridge andesite is also found as xenolith ic blocks in the Tabernacle Hill tuff cone (unit Ptc in Chapter 2).
Figure 4.5: Simplified geologic map highlighting the volcanism associated with the Beaver Ridge eruptions. Tabernac le Hill volcano can also be seen as well as parts of the Kanosh volcano, White Mount ain, and Ice Springs. 90 During this episode of increased eruptiv e activity, many of the basaltic eruptions have similar physical expressions of large ci rcumfluent lava flows, particularly the eruptions of Black Rock, Fumarole Butte, Beav er Ridge I and II, De seret, and Pahvant I lavas. This is largely a function of the pr e-existing topography, but it also represents a good locale for measuring effusivity since the calculation can be simplified in light of
areas topography. It was beyond the scope of th is project to measure the effusivity of most of these volcanoes, mainly due to many of the volcanoes having unidentified eruptive vents. The eruption of the Black Rock volca no (1.16 0.3; Best et al., 1980; Nash, 1986) followed Beaver Ridge some time later to produce a very large basaltic lava flow (Figure 4.6) that is topographi cally confined by the slopes of the Mineral and Cricket mountain ranges. Little is known about the eruptive behavior of Black Rock aside that it is a large inflated sheet flow of p hoehoe (Figure 4.7) with no mapped vents or eruptive centers. Figure 4.6 : Simplified geologic map of the Black Rock volcanic field. Deposits of the Cuday Mine, Twin Peak and Cove Creek volcanoes are shown but not in detail. 91
92 Figure 4.7 : Photograph showing the eastern flow fr ont of the Black Rock volcanic flow. (Reproduced from Hintze, 2003). Several small eruptions continued in the southern portion of th e field area until about 1 Ma and larger eruptions didnt re sume until the eruption of Cedar Grove (0.3 0.1; Best et al., 1980). Meanwhile, the large an desitic eruption of Fumarole Butte (0.9 0.1; Best et al., 1980) covered a large portion of the desert floor to the north. The surficial expression of the Fumarole Butte complex (Figure 4.1) is an impressive large circular flow around its central cinder cone, much lik e Tabernacle Hill (Figure 4.17) and Ice Springs (Figure 4.18). Around the same time ( 0.8 0.1; Hoover, 1974; Best et al., 1980) volcanism resumed in the Beaver Ridge area with the Beaver Ridge I basaltic flows (Figure 4.5). Very near and to the east of the Beaver Ridge activity, the Kanosh volcanoes began to erupt. The Kanosh field, though highly eroded, has the most mapped vent exposures (8) of any of the deposits studied ( Figure 4. and Figure 4.9).
Figure 4.8 : Simplified geologic map of the Kanosh volcanic field (Black Rock volcano). 93 Figure 4.9 : Photograph looking northeast at the main vent complex of the highly eroded Kanosh volcano.
94 Somewhat anomalously, the next eruptions in the Black Rock volcanic cluster are a series of rhyolite domes (9) formed at the summit of northern Mineral Mountain range (Figure 4.1). The rhyolite of the Mineral M ountains (0.6 0.85 Ma; Lipman et al., 1978; Bowman et al., 1982) is thought to represent shallow silicic chambers that still possess enough latent heat to power the nearby Roos evelt Geothermal Power Plant (Evans and Nash, 1978; Nash and Crecraft, 1982). The eruption of Cove Fort (0.5 0.1; Ev ans et al., 1980), located in the southern portion of the field area, produced a large ci nder cone that was subsequently cut by a Quaternary fault, giving it an unusual dual peak morphology (Ross and Moore, 1985). Following the Cove Fort eruption, the locus of activity moved northward again with the small rhyolite dome eruption of White Mount ain and Deseret volcano. Neither Deseret nor White Mountain have mapped vents. The White Mountain rhyolite dome (Figure 4.1) is located ~1 km east-southeast of Tabernacle Hill volcano and has th e smallest surficial expression in the Black Rock cluster of 0.69 km2. I hypothesize that the small subaerial portion of the dome is merely a reflection of much larger dome buried at some depth. This is evidenced by the rhyolite blocks found interbedded within the Tabernacle Hill tuff cone ( Figure 4. ). The Deseret volcano in the western portion of the map area ( Error! Reference source not found. and Figure 4. ) is another large lava flow with no mapped vents. The poor dating of the Deseret volca no (0.4 0.4 Ma; Best et al., 1980) makes it hard to place in terms of the overall cluste r evolution. However, Deseret does have Lake Bonneville shorelines on it, thus givi ng it a bare minimum age of > 0.015 Ma.
Figure 4.10 : Simplified geologic map highlighting the volcanism associated with the Cove Fort area of the Black Rock volcanic cluster. 95
Figure 4.11 : Photograph showing a rhyolitic xeno lith found in the Tabernacle Hill tuff cone. 96
Figure 4.12: Simplified geologic map highlight ing the Deseret volcano. The eroded remnants of the undated Sunstone Knoll volcano is seen in the southern portion of the map. The eruptions of the Smelter Knolls in th e northern part of the field represent a truly bimodal sub-field within the BRVC. The eruptions span from the initial andesitic eruptions around 6 Ma, to the rhyolitic erupti ons at ~3.4 Ma, and finally the basaltic eruptions at 0.31 0.08 (Turley and Nash, 1980) Because of the large temporal and compositional differences between the rhyolite and basalt flows of Smelter Knoll, it is 97
likely that the two events only share the same name due to their spatial rather than temporal relationship. 98 Figure 4.13 : Simplified geologic map of the Smelte r Knoll volcanic field. The northern section of the field is primarily composed of rhyolitic deposits while the southern portion of the field is basaltic. Topogra phy is only shown on igneous deposits.
99 Figure 4.14 : Aerial photograph showing the eroded remnant of a phreatic basaltic crater in the foreground and the rhyolite domes of the Smelter Knolls in the background. (Hintze, 2003)
100 Figure 4.15 : Simplified geologic map of the Pahvant volcanic field. Also shown are the Ice Springs and Tabernacle Hill volcanic fields as well as pa rts of the Deseret, Sunstone, White Mountains and Beaver Ridge fields Topography is only shown on the Pahvant volcanic field.
Figure 4.16 : Photograph showing the west facing side of Pahvant Butte. The initial eruption of Pahvant lavas was a vast basalt flow that covered at least ~ 293 km2, making it by far the largest volume of la va associated with a single vent complex in the Black Rock cluster. Three vents are mapped for the Pahvant I eruption, all of which lead linearly north away from th e Ice Springs volcano (F igure 4.5). Based on the curvature of the p hoehoe ropes, Hoover (1974) inte rpreted these vents to be the eruptive centers for the entire flow field. The e ffusive eruptions referred to as the Pahvant I and II lava flows, are largely p hoehoe and contain many lava tubes and tumuli fields as well as sedimentary xenoliths from the lakebed near the vents, much like Tabernacle Hills lava flows (Hoover, 1974). The second effusive eruption in the Pahvant field was the Pahvant II lavas, poorly dated at 0.1475 Ma 0.1575 (Hoover, 1974), or between 2.5 and 1.25 Ma (Nelson and Tingey, 1997). This was a relatively small (~31 km2) eruption compared to its predecessor. The Pahvant II lavas are best exposed by the Devils Kitchen Fault scarp 101
102 that runs north-northwest to south-south east through the en tire field (Condie and Barsky, 1972). Both Pahvant I and II eruptions are in ferred to have occurred before the Lake Bonneville occupation of the area and are th erefore covered in varying thicknesses of lacustrine and eolian sediments (Oviatt, 1991). Finally, the last eruption in the Pahvant volcanic field was the eruption of Pahvant Butte, or Sugarloaf Mountain as it is known locally ( Error! Reference source not found. ). The eruption and resulting deposits of Pahvant Butte ha ve been instrumental in advancing the understanding of phreatomagmatic processes. The eruption began subaqueously in Lake Bonnevilles transgre ssive phase just prior to reaching the Bonneville high stand (Oviatt, 1989; White, 1996) The eruption persisted and eventually breached the water surface and continued to erupt subaerially (White, 1996). The resultant tuff cone towers >270 m above th e surrounding desert landscape and measures ~3 km in diameter at the base. The end of Episode II volcanism is not cl early defined as the dates of the very extensive Pahvant I lava flow (Figure 4.15) field are not well constrained. The location of the dated samples was not geographically well constrained either, and therefore introduces more possible erro r in the overall model. This may also contribute to underestimates of the extent of the deposits by previous mapmakers. However, based on current map boundaries for the field, the coll ective volume of the tw o effusive and one phreatic eruption is estimated to be at least 85 km3. The actual volume of the deposits may in fact be much higher owing to lack of exposure and ash dispersal both subaerially and subaqueously. This is quite anomalous co mpared to the calculated volumes for the rest of the BRVC and potentially indicates an overall increase in volume flux with time.
Tabernacle Hill volcano (38.12 N, 112 32.03 E) is located 18 km west of the town of Fillmore and was also first described and named by G.K. Gilbert in his book Lake Bonneville (1890; Figure 4. ). Gilbert imagined the volcanos central tuff cone to resemble the Temple Square building in Sa lt Lake City and named it accordingly. Like Ice Springs, Tabernacle is a small volume (0.47 km3) monogenetic volcano that summits at just ~1515 m. Planimetrically circular in shape, the lava flows cover an area of ~18.7 km2 and has a maximum relief of ~100 m. Figure 4.17 : Simplified geologic map of Tabernacle Hill volcano. The Beaver Ridge volcanic field is visible in the southern portion of the map and a small portion of the 103
104 distal lavas of Ice Springs are visible in th e north. Only the topography of Tabernacle Hill is shown The volcano has no mapped vents, though the centr al lava lake is inferred to be the eruptive source as there was no other compe lling evidence for additional vents. Unlike Ice Springs, the lavas of Tabernacle Hill ra diate from the central crater in a near equidistant fashion and are exclusively p hoehoe rather than a This is more similar to the shape and structure of the Black Rock and Deseret lava flows (Figures 4.8 and 4.12, respectively). The lavas flow partly over th e northern exposure of the Beaver Ridge andesite as well as part of the White Mountain rhyolite dome at depth. Dating of Tabernacle Hill has been somewhat inconc lusive with only an upper bound of ~14 Ka being determined from one entrai ned tufa deposit (Oviatt, 1991). While the geochemistry of Tabernacle Hills lavas is considerably less studied that those of Ice Springs, plenty of data lends its elf to process identific ation. Data sets of Condie and Barsky (1972), Hoover (1974), and Oviatt and Nash (1989) were compared to show Tabernacle Hill basalts to be alkalic to sub-tholei itic (Appendix A.11). The last and most recent eruption in the BRVC is Ice Springs volcano. Known locally as Red Dome, Ice Springs is a small volume basaltic volcano located 14.5 km from the town of Fillmore and its lavas exte nd just ~800 m from the northern edge of the Tabernacle Hill lava flows and ~ 2 km from the nearest vent of the Pahvant volcanic field ( Figure 4. ). Named by G.K. Gilbert (1890) for the i ce housed in the deep crevasses in the a flows that are sheltered from the desert sun, even in summer. The Ice Springs volcano covers a planimetric area of 45.35 km2, stands ~1520 m a.s.l., and has an approximate
volume of 0.48 km3, though this volume has slightly decreased somewhat in historic times due to heavy mining of the cinder s. Lynch (1980) reports a volume of 0.53 km3. Figure 4.18 : Simplified geologic map of the Ice Springs volcanic field. Part of the Tabernacle Hill lava flow can be seen in the south and the lavas of the Pahvant I flow cover the north half of the map. Topography is only shown on Ice Springs. The volcano is a composite of at least four eruptive centers, Gilbert (1890) proposed as many as eight, with each new ve nt partially or completely decimating the previous one (Figure 4.2). E ach eruptive center produced a flows that radiated out over 105
106 the basin floor and partly over the Pahvant volcanic field. The three largest craters, named by Gilbert (1890), are th e Crescent, Miter, and Terrace from largest to smallest. Early workers quickly recognized the freshness of the flow and Vale stero et al (1972) successfully dated the volcano based on uncharr ed roots dug from under the a a flow to 660 170 years B.P. By far the vast majority of geochemical work in the Black Rock volcanic cluster has focused on Ice Springs. Ice Springs vol cano is geochemically and petrographically different from the other volcanoes in the Bl ack Rock cluster as well as having strong variations within itself. Comparison of se veral geochemical datasets of Ice Springs basalts show it to be tholeiitic to sub-alka line (Appendix A.11). St rontium isotope data by Pushkar and Condie (1973) shows chronologi cal differences from the youngest lavas (Sr87/Sr86=0.7059) to the oldest lavas (Sr87/Sr86=0.7052).
107 4.2 Rates and Hazard Analysis To assess long-term and short-term volcanic hazards of a monogenetic field, several key factors must be considered, incl uding the age or timing of the individual events, their spatial distribution and the regional tectonic framewor k (Connor et al., 1998; Connor and Conway, 2000). This information has been combined for the volcanoes and volcanic events just described in the BRVC to create hazard estimation models that can be useful in estimating the likelihood of fu ture eruptions. Arguably, the most important information in determining the likelihood of a future eruption(s) is well-constrained age determinations of prior er uptive events (Connor and Conw ay, 2000). Here, previously available radiometric age determinations we re used to estimate recurrence rates of volcanic activity, identify temporal patterns and estimate probability of a new volcanic eruption in the Black Rock volcanic cluster. The following describes the volcanology of the area in terms of the frequency of the past eruptions leading to a statistical model describing the likelihood of future eruptions. Combining the radiometric data fr om many previously published sources (Appendix A.6), enables the empirical analysis of the repose intervals to be assessed through the calculation of th e empirical survivor func tion (Connor et al., 2000). The survivor function, S(t), is a descriptive statis tical tool used to determine the goodness of fit for a variety of distributions. (4.2)
108 which states that the probability, P that a random variable, T will exceed some value, t The 30 volcanic events, N were ranked in order from th eir calculated repose intervals (Equation 4.1) so t1 t2 tN. The survivor function is then defined by the repose interval, ti, by; (4.3) The calculated empirical survivor functi on for the entire BRVC is seen in Figure 4.19. For comparison, Figure 4.19 is re-plotted to show the relative volumes and compositions of the volcanic events with thei r sorted repose intervals. There appears to be some correlation between the repose in terval and the composition, and to a lesser extent the volume. This relationship is not clear and though intriguing, may only be coincidental.
109 Figure 4.19: Empirical survivor function of the repose intervals, ti, preceding eruptions from the data set in Appendix A.6, as a function of the repose interval. 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 00 511 522 53Survivor FunctionRepose Interval (Ma)Black Rock Volcanic Cluster
110 0 0.2 0.4 0.6 0.8 1 00 511 522 53Survivor FunctionRepose Interval (Ma) Figure 2.20 : The empirical survivor function grap hed in Figure 4.19 showing the relative volume and compositions of the BRVC events as a function of their sorted repose intervals.
111 The survivor function plotted in Figu re 4.19 based on equations 4.1 and 4.3 has an exponential form and is therefore compared to a exponential dist ribution for goodness of fit. The exponential distributi on is a special case of the Wei bull distribution that describes the times between event in a Poisson process. In a volcanological context, this implies that the volcanic events occu r continuously and independently of one another in time. The exponential distribution is given by; (4.4) where Ti is the continuous random variable (i.e. an eruptive event), is the mean of the repose intervals, and N is the number of observations. Because Ti is a continuous random variable, its probability density function can be defined using an alternative parameterization (4.5) which can be combined with Equation 4.2 to give (4.6) The empirical survivor function is then compared with the exponential distribution in Figure 4.21 for the entire BRVC as well as for the three episodes of volcanism (Figures 4.22-4.24).
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 00 511 522 53Survivor FunctionRepose Interval (Ma) 112 igure 4.22 : Empirical survivor function for obser ved repose intervals associated with e BRVC. The empirical survival function is shown as red diamonds while the estimated xponential distribution is shown by a solid line. F th e
113 3 : Empirical survivor function for the Episode I volcanism (9.1 Ma to ~1.5 a) Figure 4.2 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 00 511 522 53Survivor FunctionRepose Interval (Ma)Episode I M
114 Figure 4.24 : Empirical survivor function (red diamonds) and exponential distribution estimation (continuous line) for Episode II volcanism in the BRVC. 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 0.10.20.30.40.50.6Survor FunctionRepose Interval (Ma)Episode II
0 0.2 0.4 0.6 0.8 1 1.2 00.0020.0040.0060.0080.010.0120.0140.0160.018Survivor FunctionRepose Interval (Ma)Episode III Figure 4.25 : Empirical survivor function (red diamonds) and exponential distribution estimation (continuous line) for Episode III volcanism in the BRVC. 115
116 Based on the information displayed by Fi gures 4.22 to 4.25, the estimation of the distribution of the volcanic activity in this area appears to follow a Poisson process, at least for the last 1.16 Ma, since the Beaver Ridge andesite flow The scarcity of the data available to analyze Episode I and III make it hard to discern the goodness of fit. Nonetheless, this suggests that volcanic events in the cluster are independent of one another in time. Therefore the probability of an eruption does not depend on the time elapsed since the previous volcanic event, and probability of volcanic events in a future time interval can be estimated using a Poisson process probability model. For a Poisson process the probability th at an event will likely occur over some period of time is given by (4. 7) where P is the probability of an event over some time interval, and t is the time period of interest. In this study I define t as 1 Ka, though the temporal relationship is linear and probability will increase pr oportionally with time. The average recurrence rate for the entir e Black Rock volcanic cluster since ~9 Ma is 3.18 x 10-6 events per year, while the more recent (1.5 0.00066 Ma) activity has a higher rate of 1.2 x 10-5 events per year. Again, this may re flect an actual rate increase, an under-recording of events in the Black Rock volcanic cluster, or a combination of both. Based on the available radiometric dates and current mapping, there is a 9.5 x 10-3 or a ~1 % likelihood of a volcanic event in th e BRVC in the next 1 Ka based on the data of Episode II volcanism. Applying the same method to the la st four eruptions, Episode
117 III, the probability is somewhat higher at 7.7 x 10-2 or approximately an 8% probability of an eruption in the next 1000 yrs. An interval estimate was necessary to re port probabilities with some confidence; this was performed only for Episode II and III pe riods of activity. The interval estimate is given by: (4.8) where ti is the repose interval before the ith eruption or event and n is the total number of repose intervals. The interval esti mate (at 95% confidence) is then (4.9) which states that the mean re pose interval has a probability, P of occurring in some interval, based on a 2 distribution with 2n degrees of freedom, at a given confidence interval, This returns an likelihoo d of 1.6 x 10-3 to 7.0 x 10-3, or 0.16% to 0.7 % (with 95% confidence) an eruption in the BRVC ba sed on the steady state recurrence rate of 1.2 x 10-5 in Episode II. The same calculation for Episode III volcanism estimates the likelihood of a volcanic eruption over th e next 1 Ka to be between 2.33 x 10-1 and 2.01 x 10-2, or between a 2.0% and 23.3% (with 95% confidence). The point estimate probabilities calculated from Equation 4.7 of 1% and 8% for Episodes II and III, respectively, fall well within the interval estimate ranges given and are therefore considered to have good correlation.
4.3 Evolution of the Black Rock Volcanic Cluster The BRVC has been active for the last 9.1 Ma and increased activity has been observed over the last 1.5 Ma. This repres ents a long-lived clus ter that has overall recurrence rates comparable to small volcanic fields throughout the Basin and Range (Table 4.1). However, the last two episodes of volcanism discussed in this chapter appear to reflect recurrence rates comparable, but st ill much less than, to the largest volcanic fields in Basin and Range. Table 4.1 : Some physical characteristics of severa l monogenetic volcanic fields in Basin and Range settings. Volume calculations were not available for al l fields. After Connor and Conway, 2000. Volcanic Field Basaltic events Andesitic and Rhyolitic events or complexes Area (km2) Age Range (Ma) t (events/Ma) Volume Flux (km3/Ma)Data Sources Big Pine volcanic field24 15001.2-0.121.8---Ormerod et al., 1991 Black Rock Cluster, UT17 138,5009.1-0.000663.213.5 this report Camargo volcanic field308 03,0004.7-0.0966.325.6Aranda-Gomez et al., 2003 Coso volcanic field54 381,2002.0-045.5--Duffield et al., 1980; Bacon, 1982 Pancake, NV75 025006-0.313.0---Foland and Bergman, 1992 SP Cluster, San Francisco, AZ 606 81,2005.6-0109.5--Tanaka et al., 1986; Conway et al., 1998 Springerville, AZ409 03,0002.1-0.3 226.7166.7 Condit et al., 1989; Condit and Connor, 1996 Trans-Mexican Volcanic Belt, Mexico 109612040,0003.5-0347.18.9 Hasenaka and Carmichael, 1987; Connor, 1990 Southwestern Nevada Volcanic Field 17 01,2004.6-0.0773.81.3Valentine and Perry, 2007 There are several possible explanations for the apparent rate increase seen in Figure 4.2. First, it is possible there was an actual increased rate of volcanism in the BRVC and the data are an accurate reflection of this. However, there are several ways in which this can be interpreted. One way is just an actual increased in BRVC volcanism 118
119 while another is that this increase is actua lly just the waxing phase of large cycle of volcanic activity that just is not resolvable with the data set available. Or the rate change seen in Figure 4.2 may simply be due to an incomplete record for older volcanic events. This is very plausible concept since it is onl y the oldest deposits that have large gaps in time between mapped eruptions, possibly due to high sedimentation and burial. It should be noted, however, that 12 deep (>500 m) (Hin tze, 2003) exploration dr ill core logs were examined and showed no evidence of buried igneous deposits, though if buried volcanoes did exist they would be easy to miss based on the small-volume nature of the other volcanoes in the area. Finally, several volcanic events in the cluster were not included because they simply have not been dated at al l. The addition of all of the deposits in the Black Rock volcanic cluster along with any shifts associated with the deposits that have large errors may change the appearance of the temporal distri bution all together. Based on the available data, three arbitrary episodes of volcanism are proposed to account for the observed have created the Black Rock cluster. Episode I began ~9 Ma with the rhyolitic eruption of Gillies Hill (Evans et al. 1980) and culminated around 2.11 Ma with the eruption of Burn t Mountain (Nash, 1986). Largely confined to the southern portion of the cluster, this episode of volcanism produced at least 11 separate deposits, most of which were rhyolitic or andesitic and had an annual recurrence rate of ~ 1.43 x 10-6 events yr-1. (Figure 4.2; Appendix A.6). Episode II volcanism began ~1.5 Ma with the andesitic eruption of Beaver Ridge (Nas h, 1986) and lasted until ~150 Ka with the inception of a series of eruptions in the Pahvant area (Hoove r, 1974). This phase was the most productive, with 15 events, or 1.04 x 10-5 events yr-1. Predominately mafic, Episode II only produced four rhyolitic and andesitic events. Finall y, Episode III recurrence rates
120 are significantly higher, 1 x 10-4 events yr-1. Episode III is the smallest of the three episodes, during which the activ ity and styles of the eruptio ns are very similar to one another, all basaltic. This episode is infe rred to have begun 31.5 Ka (Hoover, 1974) with the second in a series of three Pahvant erup tions and ended ~600 B.P. with the eruption of Ice Springs (Valestro et al., 1972). The Tabernacle Hi ll eruption occurred during Episode III.
121 Chapter 5 Conclusions Tabernacle Hill volcano is one of the many Quaternary volcanic vents located in the Black Rock volcanic cluster. Base d on field mapping at the 1:24,000 scale, a geological map of Tabernacle Hill volcano is pres ented in this work. The level of detail is improved in comparison to previously published geologic maps, with eight mapped units of lava flows, tephra, pyro clasts and lava tubes. At least two overflow events are indicated by the rafted sections of tuff cone on the distal edges of the lava flows. A study of the entire stratigraphic secti on clearly shows the episodic be havior of the final effusive and explosive eruptive stages. It is hypothesi zed that the Tabernacle Hill lava flows did not interact directly with La ke Bonneville but rather erup ted into a wet marsh-like or even snowy environment, sufficient enough to produce a tuff cone and isolated pillow lavas. This allowed subsequent eruptive epis odes, with higher mass flow rates, to be effectively armored from the formerly wet e nvironment and therefor e less explosive in nature. The lava lake within the crater probably fluctuated many times, resulting in a myriad of volcanic features within the crater before it drained for the last time. Ballistic analysis shows that the most explosive phases of the eruption were able to transport large basaltic blocks hundreds of meters from th e vent at velocities between 60-70 m/s. Tabernacle Hill is estimated to have expl osive energy yields on the order of 1 kT. Volcanism in the BRVC has been long-lived and widespread with more than 30 volcanic vents and events mapped across ~ 8,500 km2 area of west-central Utah (Figure
122 1.2 and Figure 4.1). The time span of volcanic activ ity in the cluster is late Miocene (~ 9 Ma, Gillies Hill) to the Ho locene (~ 600 yrs., Ice Springs). Age determinations for individual volcanic events were used to es timate temporal recurre nce rates of volcanism (Figure 4.1) and to correlate ra tes of volcanic activity with ot her factors such as rates of crustal extension, faulting and changes in geochemistry. The hazard analysis is shown to be heavily dependent on the radiometric da ting methods and may not reflect the true temporal nature of volcanism in the Black Rock volcanic cluster. However, the data shows that despite the recent eruption of Ice Springs (~600 yrs ago), there is a ~8 % chance of a volcanic eruption in the Black Ro ck volcanic cluster in the next 1 ka. An interval estimate over the same period gi ves between 0.1% and 24% chance (with 95% confidence) of a volcanic eruption in the Black Rock volcanic cluster over the next 1 ka. The study of the eruption of Tabernacle Hi ll volcano, coupled with other geologically recent volcanic activity in the area, has le d to more probing questions regarding the frequency of eruptive events in the region. Ar e future volcanic er uptions expected in west-central Utah? What is the likelihood of such eruptions in the coming decades?
References Aranda-Gmez, J. J., Luhr, J. F., Housh, T. B., Connor, C. B., and Becker, T., 2003, Synextensional Pliocene-Pleistocene erupt ive activity in the Camargo volcanic field, Chihuahua, Mxico: Geological So ciety of America Bulletin, v. 115, p. 298313. Bacon, C. R., 1982, Time-predicable bimodal vol canism in the Coso Range, California: Geology, v. 10, p. 65-69. Batiza, R., and White, J. D. L., 2000, Submarine Lava and Hyaloclastite: in Encyclopedia of Volcanology, Academic Press, p. 361-382. Best, M. G., McKee, E. H., and Damon, P. E., 1980, Space-time-composition pattern of late Cenozoic mafic volcanism, Southwestern Utah and adjoining areas: American Journal of Science, v. 280, p. 1035-1050. Bowman, J. R., Evans, S. H., Jr., and Nash, W. P., 1982, Oxygen-isotope geochemistry of Quaternary rhyolite from the mineral mountains, Utah, USA: Department of Energy Contract AC07-79ID12079. Cerling, T. E., and Craig, H., 1994, Geomor phology and in-situ cosmogenic isotopes: Annual Review of Earth and Pl anetary Sciences, v. 22, p. 273-317. Colgate, S. A., and Sigurgeirsson, T., 1973, D ynamic mixing of water and lava: Nature, v. 244, p. 552-555. Condie, K. L. and Barsky, C. K., 1972, Origin of Quaternary Basalts from the Black Rock Desert region, Utah: Ge ological Society of Am erica Bulletin, v.83, p. 333-352. Condit, C. D., L. S. Crumpler, J. C. A ubele, and Elston, W. E., 1989, Patterns of Volcanism along the Southern Margin of the Colorado Plateau: The Springerville Field: Journal of Geophysic al Research, v. 94, p. 7975. Connor, C. B., 1990, Cinder Cone Clustering in the Trans-Mexican Volcanic Belt: Implications for Structural and Petr ologic Models: Jour nal of Geophysical Research, v.95, p.19,395-19,405. Connor, C. B. and Hill, B. E., 1995, Three non-homogenous Poisson models for the probability of basaltic volcanism: A pplication to the Yucca Mountain region, Nevada, USA: Journal of Geophysical Research, v.100, p.10,107-10,125. 122
Conway, F. M., Connor, C. B., Hill, B. E., C ondit, C. D., Mullaney, K., and Hall, C. M., 1998, Recurrence rates of basa ltic volcanism in the SP Cluster, San Francisco volcanic field, Arizona: Geology, v.26, p. 655-685. Connor, C. B., and Conway, F. M., 2000, Basalt ic Volcanic Fields: in Encyclopedia of Volcanology, Academic Press, p. 331-344. Connor, C. B., McBirney, A. R., and Furla n, C., 2006, What is the probability of explosive eruption at a long-dormant vol cano?: in Statistics in Volcanology (Mader et al., eds.), Geological Society, London Duffield, W. A., Bacon, C. R., and Dalrym ple, G. B., 1980, Late Cenozoic volcanism, geochronology, and structure of the Coso Range, Inyo County, California: Journal of Geophysical Research, v. 85, p. 2381-2404. Evans, S. H., Jr., and Nash, W. P., 1978, Quat ernary rhyolite from th e Mineral Mountains, Utah, USA: Department of Energy Contract EY-76-S-07-1601. Evans, S. H., Jr., Crecraft, H. R., and Nash, W. P., 1980, K/Ar ages of silicic volcanism in the Twin Peaks/Cove Creek dome area: Isochron/West, v. 28, p. 21-24. Evans, S. H., and Steven, T. A., 1982, Rhyolite s in the Gillies Hill-Woodtick Hill area, Beaver County, Utah: Geological Soci ety of America Bulletin, v. 93, p. 11311141. Fagents, S. A., and Wilson, L., 1993, Explosive Volcanic Eruptions VII. The ranges of pyroclasts ejected in tr ansient volcanic explos ions: Geophysics Journal International, v. 113, p. 359-370. Farrand, W. H., 2003, Discrimination of Hydrovo lcanic tephras from volcanic and nonvolcanic backgrounds in hyperspectral data of Pahvant Butte and Tabernacle Hill, Utah: Relevance for Mars: Lunar and Planetary Science, v. 34. Fisher, R. V., and Schmincke, H. U., 1984, Py roclastic Rocks: Springer, Berlin 472 p. Gilbert, G. K., 1890, Lake Bonneville: United States Geological Survey Monograph 1, 438 p. Godsey, H. S., Currey, D. R., and Chan, M. A., 2005, New evidence for an extended occupation of the Provo shoreline and imp lications for regional climate change, Pleistocene Lake Bonneville, Utah, US A: Quaternary Research, v. 63, p. 212-223. Harris, A. J. L., Dehn, J., and Calvari, S., 2007, Lava effusion rate definition and measurement: a review: Bulleti n of Volcanology, v. 70, p. 1-22. 123
Hasenaka, T., and Carmichael, I. S. E., 1987, The cinder cones of Michoacn-Guanajuato, central Mexico: Petrology and chemistr y: Journal of Petrology, v. 28, p. 241-269. Heiken, G. H., 1971, Tuff Rings: Examples from the Fort Rock-Christmas Lake Valley Basin, South-Central Oregon: Journa l of Geophysical Research, v.76, p. 56155626. Hintze, L. F., 1980, Geologic map of Utah: Utah Geological and Minera l Society Map A1, scale 1:500,000. Hintze, L. F., Davis, F. D., 2003, Geology of Millard County, Ut ah: Utah Geologic Survey, Bulletin 122. Hon, K, Kauahikaua, J., Denlinger, R., and MacKay, K., 1994, Emplacement and inflation of p hoehoe sheet flows: Observations and measurements of active lava flows on Kilauea Volcano, Hawaii: Geological So ciety of America Bulletin, v. 106, p. 351370. Hoover, J. D., 1974, Periodic Quaternary Vol canism in the Black Rock Desert, Utah: Brigham Young University Ge ology Studies, v. 21, p. 3-72. Kilburn, C. R. J., 2000, Lava Flows and Lava Fields: in Encyclopedia of Volcanology, Academic Press, p. 291-306. Le Maitre, R. W., 1989, A Cla ssification of igneous rocks and glossary of terms, Blackwell Scientific. Lipman, P. W., Rowley, P. D., Mehnert, H. H., Evans, S. H., Jr., Nash, W. P., and Brown, F. H., 1978, Pleistocene rhyolite of the Mineral Mountains, Utah-Geothermal and archeological significance: United States Ge ological Survey Journal of Research, v. 6, p. 133-147. Lynch, W. C., 1980, Chemical trends in the Ice Springs basalt, Black Rock Desert, Utah: M.S. Thesis, University of Utah, Salt Lake City, 88 p. Mastin, L. G., 2001, A Simple Calculator of Ba llistic Trajectories for Blocks Ejected during Volcanic Eruptions: United States Geological Survey Open File Report 0145, Version 1.1. Minakami, T., 1942, On the distribution of volca nic ejecta (Part I). Th e distributions of volcanic bombs ejected by the recent expl osions of Asama: Bulletin of the Earthquake Research Institute, Tokyo, v. 20, p. 65-91. McQuarrie, N., and Wernicke, B. P., 2005, An animated tectonic reconstruction of southwestern North America sinc e 36 Ma: Geosphere, v. 1, p. 147-172. 124
Morrissey, M., Zimanowski, B., Wohletz, K., and Buettner, R., 2000, Phreatomagmatic Fragmentation: in Encyclopedia of Volcanology, Academic Press, p. 431-445. Nash, W. P., 1981, Geologic Map of the South Tw in Peak-Cove Creek area, West Central Utah: Department of Ener gy Contract DE-AC07-801D12079. Nash, W. P., and Crecraft, H. R., 1982, Evolu tion of the Quaternary Magmatic System, Mineral Mountains, Utah: Interpretations from Chemical and Experimental Modeling: Department of En ergy Contract DE-ACO7-8OID12079. Nash, W. P., 1986, Distribution, lithology, and ag es of late Cenozoic volcanism on the eastern margin of the Great Basin, west-cen tral Utah: Final Report, Department of Energy Contract DE-ACO7-80ID12079, 82 p. Nelson, S. T., and Tingey, D. G., 1997, Time-transgressive and extens ion-related basaltic volcanism in southwestern Utah and vicinity: Geologic Society of America Bulletin, v. 109, p. 1249-1265. Ormerod, D. S., Rogers, N. W., and Hawesworth, C. J., 1991, Melting of the lithosphere mantle: Inverse modeling of alkali-olivine basalts from Big Pine volcanic fields, California: Contributions to Mi neralogy and Petrology, v. 108, p. 305-317. Oviatt, C. G., 1989, Quaternary Geology of part of the Sevier Desert, Millard County, Utah: Utah geological and Mineral Survey Special Studies, v. 70, 41 p. Oviatt, C. G., and Nash, W. P., 1989, Late Pleistocene Basaltic Ash and Volcanic Eruptions in the Bonneville Basin, Utah: Geological Society of America Bulletin, v. 101, p. 292-303. Oviatt, C. G., 1991, Quaternary geology of the Black Rock Desert, Millard County, Utah: Utah Geological and Mineral Survey, Special Studies 73. OConnor, J.E., 1993, Hydrogeology, hydraulics and geomorphology of the Bonneville flood: Geological Society of America Special Paper 274, 83 p. Perry, F. V., Cogbill, A. H., and Kelley, R. E., 2005, Uncovering Buried Volcanoes at Yucca Mountain: Eos Transactions of the American Geophysical Union, v. 86, DOI: 10.1029/2005EO47000. Peterson, J.B., and Nash, W.P., 1980, Geology and Petrology of the Fumarole Butte complex, Utah: Utah Geological and Mi neral Survey Special Studies 52. Peterson, D.W., and Tilling, R.I., 2000, Lava Flow Hazards: in Encyclopedia of Volcanology, Academic Press, p. 957-972. 125
Press, W. H., Vetterling, W. T., Teukolsky, S. A., and Flannery, B. P., 1992, Numerical recipes (2nd ed.): Cambridge, Cambridge University Press, 933 p. Pushkar, C., and Condie, K.C., 1973, Origin of the Quaternary Basalts from the Black Rock Desert, Utah: Strontium-isotope ev idence: Geological Society of America Bulletin, v. 84, p. 1053-1058. Ross, H. P., and Moore, J. N., 1985, Geophysical investigations of the Cove FortSulphurdale geothermal system Utah: Geophysics, v. 50, p. 1732-1745. Rowland, S. K. and Walker, G. P. L., 1990, P hoehoe and a in Hawaii: volumetric flow rate controls the lava structure: Bulletin of Volcanology, v. 52, p. 615-628. Self, S., Keinle, J., and Huot, J.P., 1980, Ukin rek Maars, Alaska, II. Deposits and the formation of the 1977 craters: Journal of Volcanology and Geothermal Research, v. 7, p. 39-65. Sheridan, M.F., and Wohletz, K.H., 1983, H ydrovolcanism: Basic considerations and review: Journal of Volcanology and Geothermal Research, v.17, p. 1-29. Sherwood, A. E., 1967, Effect of drag on partic les ejected during explosive cratering: Journal of Geophysical Research, v. 72, p. 1783-1791. Sohn, Y. K., 1996, Hydrovolcanic processes fo rming basaltic tuff rings and cones on Cheju Island, Korea: Geological Soci ety of America Bulletin, v. 108, p. 11991211. Stovall, W. K., Houghton, B. F., Harris, A. J. L. and Swanson, D. A., in press A frozen record of density-driven crustal overturn in lava lakes: the example of Kilauea Iki 1959: Bulletin of Volcanology. Sumner, J. M., 1998, Formation of clastogeni c lava flows during fi ssure eruption and scoria cone collapse: th e 1986 eruption of Izu-Oshima Volcano, eastern Japan: Bulletin of Volcanology, v. 60, p. 195-212. Tanaka, K. L., Shoemaker, E. M., Ulrich, G. E., and Wolfe, E. W., 1986, Migration of volcanism in the San Francisco volcanic field, Arizona: Geological Society of America Bulletin, v. 97, p. 129-141. Thatcher, W., Foulger, G.R., Julian, B.R., Sv arc, J., Quilty, E., and Bawden, G.W., 1999, Present-day deformation across the Basi n and Range Province, Western United States: Science, v. 283, p. 1714-1718.41 Turley, C.H., and Nash, W.P., 1980, Petrology of late Tertiary and Quaternary volcanism in western Juab and Millard Counties, Ut ah: Utah Geological and Mineral Survey Special Studies, 52 p. 126
Valentine, G. A. and Perry, F. V., 2006, Decr easing magmatic footprin ts of individual volcanoes in a waning basalt ic field: Geophysical Res earch Letters, v. 33, p. 1-5. Valentine, G.A., Perry, F.V., Krier, D., K eating, G.N., Kelley, R.E., and Cogbill, A.H., 2006, Small-volume basaltic volcanoes: Er uptive products and processes and posteruptive geomorphic evolution in Crater Flat (Pleistocene), southern Nevada, v.118, p.1313-1330. Valentine, G. A., Krier, D. J., Perry, F. V., and Heiken, G., 2007, Eruptive and geomorphic processes at the Lathrop We lls scoria cone volcano, Journal of Volcanology and Geotherm al Research, v. 161, p. 57-80. Valestro, S., Jr., Davis, E. M., and Varela, A. G., 1972, University of Texas at Austin Radiocarbon dates IX: Radiocarbon, v. 14, p. 461-485. Vespermann, D., Schmincke, H.U., 2000, Scoria Cones and Tuff Rings : in Encyclopedia of Volcanology, Academic Press, p. 683-696. Walker, G. P. L., 1973, Lengths of lava flows: Transactions of the Royal Society of London Series A 274, p. 107-118. Walker, G. P. L., 1991, Structure, and origin by injection of lava unde r surface crust, of tumuli, lava rises, lava-rise pits, and lava-inflation clefts in Hawaii: Bulletin of Volcanology, v. 53, p.546-558. White, J.D.L., 1996, Pre-emergent construction of a lacustrine basaltic volcano, Pahvant Butte, Utah (USA): Bulletin of Volcanology, v. 58, p. 249-262. White, J. D. L., McPhie, J., and Skilling, I., 2000, Peperite: a useful genetic term: Bulletin of Volcanology, v. 62, p. 65-66. White, J. D. L., 2001, Eruption and reshaping of Pahvant Butte volcano in Pleistocene Lake Bonneville: Interna tional Association of Se dimentologists Special Publication, v. 30, p. 61-82. Wilch, T. I., and McIntosh, W. C., Miocen e-Pliocene ice-volcano interactions at monogenetic volcanoes near Hobbs Coast, Marie Byrd Land, Antarctica: United States Geological Survey Short Research Paper 074, OFR OF-2007-1047. Wilson, L., 1972, Explosive volcanic eruptions II. The atmospheric trajectories of pyroclasts: Geophysical Journal of the Royal Astronomical Society, v. 30, p. 381392. 127
128 Wohletz, K. H., 1986, Explosive magma water interactions: Thermodynamics, explosion mechanisms, and field studies: Bulletin of Volcanology, v. 48, p. 245264. Wohletz, K. H. and Sheridan, M. F., 1983, H ydrovolcanic Explosions II. Evolution of Basaltic Tuff Rings and Tuff Cones: Am erican Journal of Science, v. 283, p. 385413. Wood, C. A., and Keinle, J. 1990, Volcanoes of North America: Cambridge University Press, 354 p. Zreda, M. G., Phillips, F. M., Elmore, D., K ubik, P. W., Sharma, P., and Dorn, R. I., 1991, Cosmogenic chlorine-36 production rates in terrestrial rocks: Earth and Planetary Science Letters, v. 105, p. 94-109.
133 Appendix A.4: Stratigraphic Section
Appendix A.5: Geologic Map of the Black Rock Volcanic Cluster 134
135 Appendix A.6: Physical Attributes and geochemical reference for the Black Rock Volcanic Cluster Name Map ID Sample ID # of Mapped Vents Rock Type Age (Ma) Error (Ma) Method Area (km2) Volume (km3) Source Ice SpringsQvb1 TX-11664 basalt 000066000017C-144536042Valestro et al (1972) Pahvant ButteQvb3 Beta-252331 basalt 00141300001C-14546061Oviatt and Nash (1989) Tabernacle Hill Qvb2 Beta-238031 basalt 001432000009C141935047Oviatt (1991) Pahvant ButteQvb3 Beta-220441 basalt 00159000029C14546061Best et al (1980) Mineral MountainsQvr3 5table8 rhyolite 00220004 K-Ar 204518 Naeser et al (nd) Pahvant Lavas IQvb3 P-cl 3 basalt 00310069 K-Ar 293068578Hoover (1974) Pahvant Lavas IIQvb3 P-291 basalt 00320051 K-Ar 311848Hoover (1974) Pahvant Lavas IIQvb3 P-311 basalt 01220108 K-Ar 311848Hoover (1974) Pahvant Lavas IQvb3 brd-1023 basalt 016016 K-Ar 293068578Best et al (1980) Pahvant Lavas IQvb3 brd-33 basalt 018018 K-Ar 293068578Best et al (1980) Cedar Grove Qcg CVF-1821 andesite 0301 K-Ar 1568038Best et al (1980) Smelter Knolls Qvr1 SK 662 basalt 031008 K-Ar 05001Turley and Nash (1980) White MountainQvr2 WM76-30 rhyolite 039002 K-Ar 0701Lipman et al (1978) Deseret* Qvb5 brd-21 basalt 0404 K-Ar 3262135Best et al (1980) White MountainQvr2 no data0 rhyolite 0401 K-Ar 0701Nash (1986) White MountainQvr2 75L-230 rhyolite 043007 K-Ar 0701Lipman et al (1978) Mineral MountainsQvr3 no data9 rhyolite 0480048 K-Ar 30618Lipman et al (1978) Beaver Ridge I* Qvb6 B-04 0 basalt 0501 K-Ar 2262118Best et al (1980) Cove Fort Qcf cvf-5031 basalt 0501 K-Ar 812515Best et al (1980) Mineral MountainsQvr3 75L-169 rhyolite 05007 K-Ar 204518Lipman et al (1978) Beaver Ridge II* Qvb6 B-04 0 basalt 05220157 K-Ar 1698022Hoover (1974) Beaver Ridge II* Qvb6 B-03 0 basalt 05250122 K-Ar 1698022Hoover (1974) Mineral MountainsQvr3 75L-18A1 rhyolite 054006 K-Ar 204518Lipman et al (1978) Basalt of Kanosh Qvb7 K-078 basalt 06770123 K-Ar 3060161Hoover (1974) Basalt of Kanosh Qvb7 K-028 basalt 06770123 K-Ar 3060161Hoover (1974) Basalt of Kanosh Qvb7 K-088 basalt 06770123 K-Ar 3060161Hoover (1974) Basalt of Kanosh Qvb7 K-038 basalt 06770123 K-Ar 3060161Hoover (1974) Mineral MountainsQvr3 75L-159 rhyolite 0704 K-Ar 204518Lipman et al (1978) Mineral MountainsQvr3 75L-179 rhyolite 08506 K-Ar 204518Lipman et al (1978) Mineral MountainsQvr3 no data9 rhyolite 085085 OH 20450Lipman et al (1978) Beaver Ridge I* Qvb6 B-19 0 basalt 0875008 K-Ar 2262118Hoover (1974) Fumarole Butte Qfb 76-31 andesite 08801 K-Ar 9835865Peterson and Nash (1980) Fumarole Butte Qfb 76-3G1 andesite 08801 K-Ar 9835865Peterson and Nash (1980) Fumarole Butte Qfb 76-361 andesite 08801 K-Ar 9835865Peterson and Nash (1980) Fumarole Butte Qfb 76-91 andesite 08801 K-Ar 9835865Peterson and Nash (1980) Beaver Ridge I* Qvb6 B-12 0 basalt 0901 K-Ar 2262118Best et al (1980) Beaver Ridge I* Qvb6 B-12 0 basalt 09560101 K -Ar 2262118Hoover (1974) Beaver Ridge I* Qvb6 B-10 0 basalt 09870085 K-Ar 2262118Hoover (1974) Black Rock Flow* Qvb9 320 basalt 103 K-Ar 7688303Best et al (1980) Crater Knoll Qck cvf-5011 basalt 103 K-Ar 1563012Best et al (1980) Fumarole Butte Qfb d2252-c1 andesite 101 K-Ar 9835865Best et al (1980) Cunningham HillQvbx cvf-5000 basalt 1103 K-Ar 14020008Best et al (1980) Black Rock Flow* Qvb9 no data0 basalt 132009 K-Ar 7688303Nash (1986) Beaver Ridge Qva1 no data2 andesite 1502 K-Ar 1994062Nash (1986) Burnt Mountain Tbm no data1 basaltic andesite 211036 K-Ar 1507029Nash (1986) Cuday Mine*Tvrx no data rhyolite 222008 K-Ar 343394Leudke and Smith (1978) Lava Ridge* Tlr no data1 basalt 222051 K-Ar 1141051Nash (1986) Cuday Mine*Tvrx 75L-21 rhyolite 233012 K-Ar 343394Lipman et al (1978) Cuday Mine*Tvrx CC77-4 rhyolite 23508 K-Ar 343394Evans et al (1981) Cuday Mine*Tvrx CC77-8 rhyolite 23508 K-Ar 343394Evans et al (1981) Twin Peak Tvr2 no data8 rhyolite 235008 K-Ar 3666Nash (1986) Twin Peak Tvr2 no data0 rhyolite 235014 K-Ar 3666Leudke and Smith (1978) Cuday Mine*Tvrx 75L-19 rhyolite 238015 K-Ar 343394Lipman et al (1978) Cuday Mine*Tvrx CC77-19 rhyolite 243012 K-Ar 343394Evans et al (1981) Twin Peak Tvr2 no data8 rhyolite 243008 K-Ar 3666Nash (1986)
136 Appendix A.6 (continued) Name Map ID Sample ID # of Mapped Vents Rock Type Age (Ma) Error (Ma) Method Area (km2) Volume (km3) Source Twin Peak Tvr2 no data0 rhyolite 243008 K-Ar 3666Nash (1986) Twin Peak* Tvr2 CC78-300 rhyolite 243008 K-Ar 3666Evans et al (1981) Cove Creek Tvb1 cvf-5041 basalt 2504 K-Ar 3058039Best et al (1980) Twin Peak* Tvr2 no data rhyolite 251008 K-Ar 3666Nash (1986) Twin Peak* Tvr2 CC77-200 rhyolite 251008 K-Ar 3666Evans et al (1981) Cuday Mine*Tvrx CC77-18 rhyolite 254008 K-Ar 343394Evans et al (1981) Cuday Mine*Tvrx no data rhyolite 254009 K-Ar 343394Nash (1986) Cuday Mine*Tvrx CC79-81 rhyolite 263009 K-Ar 343394Evans et al (1981) Cuday Mine*Tvrx no data rhyolite 26301 K-Ar 343394Nash (1986) Cove Creek Tvb1 CC77-91 basalt 26501 K-Ar 3058039Evans et al (1981) Coyote Hills* Tvrx no data rhyodacite 26701 K-Ar 08302Nash (1986) Coyote Hills* Tvrx CC79-2 rhyolite 26701 K-Ar 08302Evans et al (1981) Coyote Hills* Tvrx no data rhyodacite 27401 K-Ar 08302Nash (1986) Cuday Mine*Tvrx CC77-15 rhyolite 27401 K-Ar 343394Evans et al (1981) Smelter Knolls Qvr1 Sk 71 rhyolite 3401 K-Ar 81001Turley and Nash (1980) Smelter Knolls Qvr1 SK 34 rhyolite 3401 K-Ar 81001Turley and Nash (1980) Smelter Knolls Qvr1 SK-45 rhyolite 3401 K-Ar 81001Turley and Nash (1980) Smelter Knolls Qvr1 SK-75 rhyolite 3401 K-Ar 81001Turley and Nash (1980) Fumarole Butte Mfb d3351-3 basalt 5304 K-Ar 236028Best et al (1980) Fumarole Butte Mfb csv-76-14 basalt 603 K-Ar 236028Best et al (1980) Fumarole Butte Mfb 76-14 basalt 60301 K-Ar 236028Peterson and Nash (1980) Smelter Knolls Qvr1 SK-72 andesite 6105 K-Ar 040025Best et al (1980) Fumarole Butte Mfb 76-8A rhyolite 61801 K-Ar 0322003Peterson and Nash (1980) Fumarole Butte Mfb 76-120 rhyolite 61801 K-Ar 0322003Peterson and Nash (1980) Gillies Hill Tvr3 77-32 rhyolite 9102 K-Ar 2634016Evans et al (1981) Gillies Hill Tvr3 79-12 rhyolite 9102 K-Ar 2634016Evans et al (1981) Gillies Hill Tvr3 77-62 rhyolite 9102 K-Ar 2634016Evans et al (1981) Gillies Hill Tvr3 77-82 rhyolite 9102 K-Ar 2634016Evans et al (1981) Gillies Hill Tvr3 77-72 rhyolite 9102 K-Ar 2634016Evans et al (1981)
137 Appendix A.7: Vent Locations Name Latitude Longitude Ice Springs 38.9633 112.5068 Ice Springs 38.9623 112.5073 Ice Springs 38.96 112.507 Ice Springs 38.9648 112.5069 Tabernacle Hill 38.9082 112.5336 Pahvant Butte 39.1272 112.5511 Pahvant Lavas II 39.0719 112.504 Pahvant Lavas I 39.9718 112.532 Pahvant Lavas I 38.987 112.538 Pahvant Lavas I 38.9963 112.543 Cedar Grove 38.543 112.6633 Smelter Knolls (basalt) 39.403 112.8536 White Mountain 38.9127 112.4909 Cove Fort 38.567 112.639 Mineral Mountains 38.479 112.811 Mineral Mountains 38.4534 112.7827 Mineral Mountains 38.4483 112.089 Mineral Mountains 38.427 112.8127 Mineral Mountains 38.419 112.8004 Mineral Mountains 38.4057 112.815 Mineral Mountains 38.4775 112.8137 Kanosh 38.8056 112.4876 Kanosh 38.7941 112.4919 Kanosh 38.7916 112.4907 Kanosh 38.785 112.4937 Kanosh 38.798 112.503 Kanosh 38.8279 112.4957 Kanosh 38.8289 112.4937 Kanosh 38.8292 112.4891 Fumarole Butte (andesite) 39.615 112.8036 Red Knoll 38.4935 112.714 Crater Knoll 38.4719 112.726 Burnt Mountain 38.6832 112.729 Cove Creek 39.6449 112.716 Gillies Hill 38.536 112.639 Gillies Hill 38.5347 112.6328 Pot Mountain 39.1289 112.7739 Sunstone Knoll 39.146 112.717 Sunstone Knoll 39.146 112.715
Appendix A.8 : Ballistic Analysis Codes To calculate the range of blocks from the vent # File: pythag_theorum.pl # By: A. Leonard # July 21, 2007 # Purpose: Use the Pythagorean Theorem to find the distance blocks have # traveled from their assumed origin. open FILE1, "ballistics.xyz" or di e "cannot open $ARGV : $!"; while ($line1 =
139 Appendix A.9 : Ballistic Analysis Variables Symbol Explanation Units A Cross-sectional area of block m2 CdDrag coefficient --D Diameter of block m2 g Acceleration due to gravity m/s2 m Mass of block kg aDensity of Air kg/m3 rDensity of Rock kg/m3 tTTotal travel time of block s t Time since ejection s V Volume of block m3 viInitial eruptive velocity of block m/s vxVelocity component in x direction m/s vzVelocity component in z direction m/s x Horizontal block distance since ejection m xfBlock distance from vent m z Vertical block distance since ejection m zventElevation of vent above sea level m zmaxMaximum vertical height of block m eElevation difference between vent and xfm aCdA)/2m kg/m2 Angle of block ejection above horizontal degrees
Appendix A.10 : Ballistic Data ) B lx Elev. (m Block IdX(m)Y(m)Z(m)Radius (m)Diameter (m)Volume (m3)Mass (kg)Area (m2) eEastingNorthingXf (m) 011.380.841.090.5516666671.1033333330.7032647341758.1618340.9561000911449.63670.00013771918.4251366716.94764307602.744333.5081 683 021.081.030.70.4683333330.9366666670.4302826331075.7065830.6890647151448.11170.00016222416.9001366705.17314307615.895341.22772 85 031.010.810.60.4033333330.8066666670.274840643687.10160780.5110673121449.61340.00018836818.4018366714.92854307609.353333.54686 75 042.051.321.320.7816666671.5633333332.0005683165001.4207891.9195218381450.86399.71962E-0519.6523366728.97644307607.18320.7053777 051.520.830.940.5483333331.0966666670.6905936041726.4840110.9445809181450.65150.00013855619.4399366730.99184307596.332322.1633 974 060.570.420.270.210.420.03879238696.980965220.1385442361449.01960.00036178617.808366738.22724307578.294321.8119905 B071.61.11.10.6333333331.2666666671.0641078522660.2696311.260127721449.12810.00011996117.9165366741.44314307566.974323.3945856 B081.461.851.240.7583333331.5166666671.8267076524566.7691311.8066339421449.6150.00010018718.4034366743.19294307555.036326.98249 54 B091.41.020.880.551.10.696909971742.2749260.9503317781449.85340.00013813618.6418366746.92214307561.489320.781316 B100.580.550.430.260.520.073622177184.05544160.2123716631452.67960.00029221221.468366756.70164307556.591314.2465119 B1111.020.570.4316666670.8633333330.336925709842.31427150.5853921581457.60660.00017600426.395366772.40994307546.224305.5436204 B121.361.081.020.5766666671.1533333330.8032729722008.1824311.0447191841458.40390.00013174927.1923366775.43374307545.71303.20869 08 B131.020.90.590.4183333330.8366666670.306659217766.64804280.5497874411463.29540.00018161432.0838366797.24834307544.246285.52900 21 B140.890.80.730.4033333330.8066666670.274840643687.10160780.5110673121464.92390.00018836833.7123366800.67624307536.125287.27850 71 B151.190.870.560.4366666670.8733333330.348769687871.92421850.5990319061465.65140.00017398934.4398366805.09854307525.813289.8163 605 B161.120.930.450.4166666670.8333333330.303008551757.52137670.5454153911466.24490.0001823435.0333366810.81314307527.694284.13977 29 B170.940.540.40.3133333330.6266666670.128857116322.14278920.3084345851466.82580.00024247335.6142366815.1514307524.648282.621214 5 B181.450.720.560.4550.910.394568853986.42213230.6503882191468.13990.00016697836.9283366821.04214307517.405282.7213564 B191.040.770.420.3716666670.7433333330.215054952537.63737990.4339673921469.45910.00020441738.2475366828.83934307512.788279.9501 271 B200.810.580.370.2933333330.5866666670.105723824264.30955910.2703165951471.4870.00025900640.2754366836.83764307507.144278.02043 53 B210.80.680.440.320.640.137258277343.14569360.3216990881473.54970.00023742242.3381366845.86834307510.691269.114539 B230.620.560.270.2416666670.4833333330.059120604147.80151090.1834777381476.1870.00031437944.9754366869.23944307507.415255.67621 17 B240.790.60.320.2850.570.096966828242.41707010.2551758631474.6070.00026657943.3954366875.5554307510.134249.5230648 B2510.770.460.3716666670.7433333330.215054952537.63737990.4339673921475.37360.00020441744.162366863.45834307494.596269.2038485 B260.80.310.440.2583333330.5166666670.072215422180.53855470.2096576761475.37010.00029409744.1585366866.14294307491.532269.87624 92 B2220.127.116.11.4066666670.8133333330.281711345704.27836260.5195496121472.3390.00018682441.1274366861.89944307476.141284.5951817 B280.690.60.320.2683333330.5366666670.080930549202.32637240.2262033981472.08240.00028313740.8708366874.58524307468.908282.96284 12 B290.640.670.40.2850.570.096966828242.41707010.2551758631473.28580.00026657942.0742366877.50394307461.241287.6904254 B300.760.510.518.104.22.168097336282.74333880.2827433391472.58050.0002532541.3689366883.99614307453.632290.6453893 B310.820.620.550.3316666670.6633333330.152824888382.06222110.3455839191471.96950.0002290740.7579366884.31774307450.217293.39973 27 B321.030.760.370.360.720.195432196488.58048950.4071504081470.81870.00021104239.6071366894.1684307433.467303.1648234 B330.850.690.350.3150.630.130924303327.31075760.3117245311471.97910.0002411940.7675366918.36784307427.264298.3686054 B340.650.490.410.2583333330.5166666670.072215422180.53855470.2096576761472.53990.00029409741.3283366943.34684307408.088307.7209 23 B350.660.640.310.2683333330.5366666670.080930549202.32637240.2262033981470.20350.00028313738.9919366956.87834307400.669311.1192 883 B322.214.171.124.5683333331.1366666670.7689498121922.374531.0147431541451.8970.0001336820.6854366996.48744307309.979393.6591717 B370.830.850.830.4183333330.8366666670.306659217766.64804280.5497874411452.08370.00018161420.8721366990.09924307312.174392.1619 741 B B B B B B 140
Appendix A.10 (continued) Block IdX(m)Y(m)Z(m)Radius (m)Diameter (m)olume (m3)Mass (kg)Area (m2) V B lx Elev. (m ) eEastingNorthingXf (m) B380.2126.96.36.199.20.0041887910.47190.0314159271455.12870.0007597523.9171367029.96574307303.372398.3721197 B390.440.410.340.1983333330.3966666670.032679526 0.1235780381454.33420.00038306723.1226367130.04444307302.352410.40852 3 B400.70.580.440.2866666670.5733333330.098677968 0.2581691031455.41440.00026502924.2028367144.30984307311.872404.7528448 B410.850.640.460.3250.650.143793314 0.3318307241455.72070.00023376924.5091367151.38174307317.653401.174542 B421.040.890.70.4383333330.8766666670.352778495 0.6036133951455.38140.00017332724.1698367145.41174307327.18390.339627 9 B430.70.730.330.2933333330.5866666670.105723824 0.2703165951455.83610.00025900624.6245367148.61024307323.447394.8279115 B441.080.880.60.4266666670.8533333330.325352954 0.5719094891457.75390.00017806626.5423367248.36524307443.963334.3222393 B451.341.080.760.531.060.623614519 0.8824733761460.72840.00014334929.5168367271.5934307438.163353.8730314 B461.221.031.10.5583333331.1166666670.729070086 0.9793478771460.57140.00013607529.3598367275.30214307435.212358.5470685 B471.060.941.140.5233333331.0466666670.600376663 0.8604124151457.63930.00014517526.4277367286.13164307422.794375.021703 B481.351.140.650.5233333331.0466666670.600376663 0.8604124151460.8560.00014517529.6444367284.15464307435.521364.3024864 B490.70.620.40.2866666670.5733333330.098677968 0.2581691031462.76230.00026502931.5507367290.64794307452.047357.020569 1 B501.291.030.870.5316666671.0633333330.629516195 0.888032251463.30420.000142932.0926367305.26464307486.017345.4423722 B511.140.990.630.460.920.407720083 0.6647610051464.03890.00016516332.8273367311.36644307491.595346.8214829 B520.90.810.450.90.381703507 0.6361725121464.33840.00016883333.1268367316.1264307494.981348.6020149 B530.880.680.790.3916666670.7833333330.251674054 0.481929041464.06050.00019397932.8489367317.63414307499.234347.3208496 B5188.8.131.52.6166666671.2333333330.982290696 1.1946778731462.5180.00012320331.3064367319.68024307506.458344.844418 B5184.108.40.206.5751.150.796328288 1.0386890711462.80920.0001321331.5976367323.8464307509.071346.8279486 B570.960.880.650.4150.830.299386973 0.5410607951464.07550.00018307232.8639367336.37224307501.582361.4044698 B581.50.750.770.5033333331.0066666670.534140719 0.7959050451464.67070.00015094433.4591367346.83054307522.824359.1188691 B591.330.891.120.5566666671.1133333330.72256057 0.973509751464.62990.00013648233.4183367351.93714307514.967367.485603 B602.11.121.360.7633333331.5266666671.863079092 1.8305362261464.00049.95306E-0532.7888367361.0714307536.558365.120788 9 B611.11.070.930.5166666671.0333333330.577723375 0.8386307061464.65710.00014704833.4455367379.48414307565.175370.1499012 B621.461.241.030.6216666671.2433333331.006378508 1.2141295681466.43720.00012221235.2256367388.24384307595.56368.431120 5 B6220.127.116.11.7866666671.5733333332.039204844 1.944157161473.91669.65784E-0542.705367416.2284307617.072390.0853186 B641.318.104.22.16883333331.2366666670.99027676 1.2011443181477.86230.00012287146.6507367426.93274307625.29398.8861987 B650.720.660.530.3183333330.6366666670.135124768 0.3183567821482.06840.00023866550.8568367435.60644307639.844404.9251321 B660.610.520.390.2533333330.5066666670.068102903 0.2016204351486.92240.00029990155.7108367444.10994307655.969411.2267102 B670.870.590.50.3266666670.6533333330.146016883 0.3352428431490.91570.00023257759.7041367445.26964307682.237410.2971318 B681.370.850.80.5033333331.0066666670.534140719 0.7959050451494.6660.00015094463.4544367442.20614307713.023406.928776 4 B691.650.921.190.6266666671.2533333331.030856925 1.2337383421498.20140.00012123766.9898367436.80094307747.746403.9980622 B701.520.80.750.5116666671.0233333330.561112553 0.8224776831499.92330.00014848568.7117367433.96774307772.025404.6889784 B711.170.961.250.5633333331.1266666670.748832973 0.9969669751503.07920.00013486771.8676367422.58474307813.229402.8924612 B721.722.214.171.12416666671.0433333330.594658828 0.8549408071503.38240.00014563972.1708367413.13964307820.161395.84379 B731.050.750.540.390.780.248474846 0.4778362431505.34890.00019480874.1373367380.23524307890.615393.1586766 B741.50.791.10.5651.130.755499103 1.0028749151505.13720.00013446973.9256367380.76864307892.438394.5044907 B751.40.610.360.3950.790.258154617 0.4901669941502.7690.00019234271.5574367352.94314307929.453390.7426777 B7126.96.36.1990.6251.251.022653859 1.227184631502.18820.0001215670.9766367333.08074307951.398388.5081765 5 7551 81.6988138 246.6949206 359.4832844 881.9462385 264.3095591 813.3823848 1559.036298 1822.675215 1500.941657 1500.941657 246.6949206 1573.790488 1019.300208 954.2587685 629.1851352 2455.726739 1990.82072 748.4674328 1335.351799 1806.401425 4657.697731 1444.308437 2515.94627 5098.012109 2475.6919 337.8119189 170.2572564 365.0422065 1335.351799 2577.142314 1402.781382 1872.082431 1486.647071 621.1871154 1888.747756 645.3865418 2556.634646 141
142 Appendix A.11 : Total Alkali vs. Silica Char t for the Black Rock Volcanic Cluster Total Alkalis-Silica (TAS) diagram of Le Maitr e et al (1989) for th e Black Rock cluster suite of rocks. Based on data from Hoover (1974), Best et al (1980) and Nelson and Tingey (1997). 0 2 4 6 8 10 12 14 16 404550556065707580Na2O + K2O (wt%)SiO2(wt. %) Ice Springs Tabernacle Hill Pahvant Butte Pahvant II Pahvant I Smelter Knoll Deseret Kanosh Beaver Ridge II Beaver Ridge I Beaver Ridge (Andesite) Cove Creek