Seamount shape and size distribution near Easter Island

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Seamount shape and size distribution near Easter Island

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Title:
Seamount shape and size distribution near Easter Island
Creator:
Rappaport, Yoav
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Tampa, Florida
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University of South Florida
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English
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viii, 128 leaves : ill. ; 29 cm.

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Easter Seamount Chain ( lcsh )
Dissertation, Academic -- Marine science -- Masters -- USF ( FTS )

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Thesis (M.S.)--University of South Florida, 1996. Includes bibliographical references (leaves 96-104).

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University of South Florida
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Universtity of South Florida
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All applicable rights reserved by the source institution and holding location.
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023512894 ( ALEPH )
37433775 ( OCLC )
F51-00127 ( USFLDC DOI )
f51.127 ( USFLDC Handle )

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SEAMOUNT SHAPE AND SIZE DISTRIBUTION NEAR EASTER ISLAND by YOA V RAPPAPORT A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science Departm e nt of Marine Science University of South Florida Dec e mber 1996 Major Pro fessor: David F. Naar, Ph. D

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Graduate School University of South Florida Tampa, Florida CERTIFICATE OF APPROVAL Master's Thesis This is to certify that the Master's Thesis of YOAV RAPPAPORT with a major in Marine Science has been approved by the Examining Committee on November 13, 1996 as satisfactory for the thesis requirement for the Master of Science degree Examining Committee: Major Professor: David F. Naar, Ph.D. Member: Sarah F. Tebbens, Ph.D. ijlrc J.

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DEDICATION This th e sis is dedicat e d to Ema

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ACKNOWLEDGMENTS I would like to thank the shipboard scientists R Beale, D Bishop, R. Hagen, A. Harris, C Jacobs, J. Korenaga, R. Nelson, R Rushy, H Vergara, A. Woods, R Batiza, D. Fontignie, R Guarda, L. Joseph, C. Kincaid, R. Moe, T Plake, B. Peroda, J -G Schilling, N Seama, R. Stefani and G. Wu I thank captain E Buck and crew for their excellent ship handling and the government of Chile for permission to survey their waters I also thank the people of Rapa Nui for their kind hospitality. Thank you S. F. Tebbens, D. L. Turcotte D. K. Smith, R Batiza, D Scheirer, C. Barton, and M. Rashid for useful discussion, and M Kuykendall for reviewing earlier versions. A special thank you to Zhengrong "Jerry" Liu, for all the help, programming, teaching and many hours of discussion. It is due to Jerry s extraordinary effort processing the data that I had a unique data set from which to work Finally, the completion of this thesis would not have been possible without the guidance and patience of my advisor David F. Naar Thank you for believing in me and providing the ideal working environment. Some figures were generated using GMT (Generic Mapping Tool) [Wessel 1991; Smith, 1990]. Funding was provided by NSF Grants OCE9116012, OCE9214494, OCE9214495, OCE9214496, and OCE9302802

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TABLE OF CONTENTS LIST OFT ABLES LIST OF FIGURES ABS1RACT TABLE OF CONTENTS CHAPTER 1 : OVERVIEW OF PREVIOUS WORK 1.1 Introduction 1.2 Seamount Formation Environments 1.2.1 Mid Atlantic Ridge (Slow Spreading Rate) 1.2.2 East Pacific Rise (Fast Spreading Rate) 1.2.3 Intraplate Environments 1.3 Formation of the Easter Seamount Chain 1.3.1 Tectonic Setting 1.3.2 Relation to the Easter Microplate 1.3.3 Seamount Ridges along the ESC 1.3.4 Hotspot Model 1.3.4.1 Simple Hotspot 1.3.4.2 Hotspot-Ridge Interaction 1.3.4 3 Hybrid Hotspot Mod e ls 1.3.5 Leaky Fracture Zone 1.3.6 Diffuse Extension Model 1.3.7 Hot Line 1.4 Rationale for Study CHAPTER 2: SEAMOUNT SHAPE AND SIZE DISTRIBUTION 2 1 Introduction 2.2 Data Set 2.3 Method Used 2.4 Shape Characteristics 2.4 1 Orientation of Basal Diameter 2.4.2 Height to Radius 2.4.3 Volume 2.4.3.1 Seamounts' Contribution to the Crust 2.4.4 Cross-sectional Area 2.4 5 Flatness and Slope 2.5 Observed Shapes and Patterns 2.6 Size Distribution iii iv Vll 1 1 5 6 6 7 8 8 9 12 15 16 17 18 21 22 22 23 24 24 24 26 34 39 39 39 41 41 43 44 61

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2 .6.1 Previous Method and Limitations 61 2.6.2 Exponential-law Distribution 62 2.6.3 Power-law Distribution 69 2.6.3.1 Height 69 2.6.3 2 Volume 74 2 6.4 Discussion 77 2 6.4.1 Implication of Shape Analysis 77 2.6.4 2 Implication of the Size Distribution 78 2.6.4.3 Geochemical Predictions 87 2 6.4.4 Implications of the Results to the Proposed Models for the Formation of the Easter Seamount Chain 88 2 7 Conclusions 93 REFERENCES 96 APPENDICES 105 APPENDIX 1. INDEX TO SEAMOUNTS USED IN THIS STUDY 107 APPENDIX 2. SHAPE STATISTICS FOR SEAMOUNTS WITH HEIGHTS GREATER THAN 200 METERS 113 11

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LIST OF TABLES Table 1. Relative and absolute plate velocities at 27S, 108W from different models 9 Table 2 Statistical Summery of 383 s e amounts 34 Table 3 Comparison of seamount distribution parameters 63 Table 4 Comparison of seamount size distribution parameters with other studies 85 ill

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LIST OF FIGURES Figure 1. Southeastern Pacific predicted bathymetry 3 Figure 2. General tectonic setting of the study area 4 Figure 3 Seafloor age isochrons and interpr e ted lava flows 10 Figure 4. Shaded ot>served bathymetry of the ESC from GLORI-B processed bathymetry data 13 Figure 5. Cartoo n s of models proposed for the formation of the Easter Seamount Chain 19 Figu re 6. Cartoon diagram re l ating th e two principal compo n e n ts of variability 25 Figure 7 Act u al b asal outlines of seamount 28 Figure 8. Shaded bathymetry plot of Getu S e amount 30 Figure 9 Relationship between approximate sea mount volume versus actual seamount volume 31 Figure 10. Simplified basal outline of seamounts with heights over 200 meters 32 Figure 11. Plot of the profile along the minimum basal diameter of the 12largest seamounts 35 Figure 12. Correlation among seven seamount shape properties 36 Fig u re 13. Orientation of maximum basal diameter 40 Figure 14. Seamounts volume contribution to the crus t 42 Figure 15 Flatness frequency distribu tion 45 Figure 16. Flatness spatial distribution 46 Figure 17 Slope frequency distribution 48 Figure 18. Slope spatial distribution 49 lV

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Figure 19. Location map of detailed study areas 51 Figure 20. Side-scan intensity of Ahu volcanic field, area "A" 53 Figure 21. Shaded bathymetry of area "A" 54 Figure 22. Shape distribution in area "A" 55 Figure 23. Side-scan intensity of area "B" 57 Figure 24. Shaded bathymetry of area "B" 58 Figure 25. Shape d istribution in area "B" 59 Figu re 26. Maximum-likelihood fit to Easter Seamou n t Chain h eig h t data, single expo n e n tial model 64 Figu re 27. Single linear least-squares fit to the exponential cumulative frequency size distribution 67 Figu re 28. Multiple linear l east-sq u ares fits to the power-law cumulative frequency size distribution 70 Figure 29. Multiple linear least-squares fits to exponential cumulative freq u ency size d istribution 7 2 Figure 30 Multiple maximum-likelihood fit to the exponential cumulative frequency of seamount height distribution 75 Figure 31. Seamount height spatial distribution 79 Figu re 32 Seamount volume spatial distrib u tion 81 Figure 33 Seamount shape parameters versus spreading rate 86 Figure 34. Age data collected from GLOR07MV cruise 90 Figure 35 Index to all383 seamounts used in this study 106 Figure 36. Detailed index to seamounts used in this study 108 v

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SEAMOUNT SHAPE AND SIZE DISTRIBUTION NEAR EASTER ISLAND by YOAV RAPPAPORT An Abstract A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science Department of Marine Science University of South Florida December 1996 Major Professor : David F Naar, Ph. D V1

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A broad chain of seamounts extends eastward from the superfast spreading East Pacific Rise, near Easter Island towards South America Several models have been proposed for the formation of this chain, yet a complete mapping of the seamounts was not previously available. This is a very active region, in which seamounts cover -27% of the seafloor, and account for -4.2% of the total crustal volume. Seamount shapes vary from small domes with steep flanks to large cones with gentle slopes, in the Easter IslandSalas y Gomez Island area (25-29S, l13-l04W) In order to quantify seamount statistics and deftne their morphological variability, basal shape, cross-sectional area, volume, flatness, and slope are plotted against height for 383 seamounts with heights greater than 200 m, based on bathymetry .data collected by GLORI-B and SeaBeam 2000, during a cruise onboard RIV Mellville in the Spring of 1993. There is no clear pattern in seamount shape distribution (slope and flatness), which suggests that seamounts from different sources may form side by side. Seamount size distributions for volume and height are ftt by a power-law and exponential-ftt cumulative frequency distribution. There are at least two sub-groupings in both the volume and height distributions. Sharp changes in slope on the power-law distribution are seen at 1200 km3 and 2450 m in the volume and height cumulative frequency distribution, respectively These slope changes could be due to an underlying difference in the physical processes controlling this seamount population. According to this hypothesis, larger seamounts with heights greater than 2450 m and volumes greater than 1200 km3 formed by low viscosity flows from a warm plume source. and smaller seamounts formed by viscous flows from a cooler ridge sauce. The data support a model for the formation of the chain which predicts mixing of plume and ridge material, at several locations relatively near the ridge axis, aswell as shearing of this material at depth. The data do not favor models which predict contemporaneous volcanism along the entire length of the chain, or a simple hotspot model which predicts a single linear Vll

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increase of sea mount ages wes t to east. Additional geochemistry data wi ll he lp further refin e how this chain was formed. Abstract Approved: Major Profe sso r; oa(id F Naar, Ph.D Profes sor, D ep artment of Marine Science Date Approved: Vlll

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CHAPTER 1: OVERVIEW OF PREVIOUS WORK 1.1 Introduction A broad chain of seamounts extends from the East Pacific Rise (EPR) eastward towards South America in the southwestern Pacific (Figure 1). Based on the analysis of side-scan and bathymetry data collected on a GLORI-B [Somers and Hugget, 1993] expedition in early 1993 [Naar et al., 1993a; Naar et al., 1993b], it is shown here that seamounts in the Easter-Salas y Gomez Islands area (25-29S, l13-1040W) show a variability in shape and size distribution [Rappaport et al. 1994]. Recent bathymetric and side-scan surveys in this area report a variability of seamount shape character as well [Danobeitia et al., 1995; Hagen eta/., 1990; O'Conner et al., 1995; Stoffers et al., 1994]. With nearly complete bathymetric coverage available (Figure 2) this study quantitatively describes the shape and size distribution of the entire seamount population of a superfast spreading region influenced by a hotspot for the ftrst time As with other recent studies in the Pacific Ocean describing seamount population parameters [Abers et al., 1988; Bemis and Smith, 1993; Scheirer et al., 1996; Smith and Jordan, 1988], this study includes seamounts much smaller than 1 km in height, as originally defined by Menard [1964]. The study of spatial distribution of seamount shapes and sizes may provide information about melt delivery to the oceanic crust, and is important in understanding the lithosphere, its character, evolution and origin [Fomari et al., 1987a; Scheirer and Macdonald, 1995; Shen eta/., 1993; Shen et al., 1995; Smith and Cann, 1992; Smith and Cann, 1993]. Scientists study seamount morphology in order to gain a better 1

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understanding of the chemical character of the extruding magma, its availability, and the nature of the plumbing system [Batiza, 1989; Batiza and Vanko, 1984; Fomari et al. 1988; Searle, 1983; Smith and Cann, 1993]. Studies have been conducted in a variety of tectonic regimes: in slow spreading regions of the Atlantic distant from hotspots [Smith and Cann, 1990]; in slow spreading regions influenced by hotspots such as Iceland [e.g. Magde and Smith, 1995] ; and fast spreading regions of the Pacific distant from hotspots [Abers et al., 1988; Alexander and Macdonald 1996; Batiza, 1982 ; Fomari et al., 1987b; Scheirer et al. 1996; Smith and Jordnn, 1988]. However, none has described the distribution and morphology of seamounts in a superfast spreading, near hotspot environment, as this study does Seamount petrology and geochemistry have been studied to determine the composition of the oceanic crust and lithosphere and aid in the understanding of the earth s origin, differentiation and mantle processes [Allan et al., 1989; Batiza and Vanko, 1984; Haase and Devey, 1996 ; Poredn et al., 1993a; Zindler et al., 1984] Such analysis yield a great deal of detailed information but are expensive, time consuming, and generally unavailable for the entire seamount population In this study seamounts are classified and their shape parameters quantitatively described, such that inferences can be made about their mode of formation, in absence of complete geochemical results It is then possible to make predictions about their petrology based on preliminary results [R. Batiza, 1996, personal communication; Naar et al. 1993b ; Poredn et al., 1993a], previous geochemical results in this area [Fontignie and Schilling, 1991; Haase and Devey, 1996; Stoffers et al. 1994], and results from other studies [e g Allan et al., 1989; Batiza et al., 1989 ; Batiza and Vanko, 1984; Fornari et al., 1988; Zindler et al., 1984]. 2

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o -10 -20 -30 -40 -140 -130 120 -110 -100 -90 -so -70 Figure 1. South eas t ern Pacific predicted bathymetry. Imag e shows seafloor d e pth predicted from ETOP0-5 data, and free-air gravity anomalies calculated from the Geosat altimetric data, with further proce ss ing [Liu, 1996]. Som e major f ea tures of the southeastern Pacific are included as well as the location of thi s study area, thick black envelope The plate boundaries, thin black line, are from digiti ze d global plate boundary. White bord e r is the outline of the region seen in Figure 2. 3

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-20" -25" -30 PACIFIC rc:i -35" motion [Gripp,l994] motion [Liu 1996] pc-nz relative motion [Dlets, 1994] -125" -120 -115" 110 rate N/A ......... 150mmyr1 NAZCA ANTARCTIC -105 -100 Figure 2. General tectonic setting of the study area. The boundaries of the major tectonic plates are shown by medium thickness black lines; Pacific, Nazca, Antarctic, Easter microplate (EMP), and Juan Fernandez microplate (JFMP). Easter Island (EI), and Salas y Gomez Island (SYG) locations are marked with a filled star and triangle, respectively. GLORI-B leg 5, 6 and 7 cruise track are shown by a thin black line, and the study area is show as a thick black envelope. The Nazca-Pacific relative plate motion vector is calculated from NUVEL-1A model at 27S and 108W, trending 100, at a full rate of 150 mm yr"1 [DeMets et al., 1994]. Nazca-hotspot absolute plate motion direction is trending 85 with an undetermined rate based on a Nazca best-fit Euler pole to three hotspot chains [Liu, 1996], Table 1. The Nazca-hotspot absolute plate motion vector is trending 123, at a rate of 16 mm yr"1 [Gripp 1994] 4

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1.2 Seamount Formation Environments Based on the geometric form of seamounts, inferences may be made about the physical properties (viscosity, effusion rate and ultimately temperature) of the lava during the edifice building process [Binard et al., 1991; Fomari et al., 1987b; Macdonald et al., 1993; Magde and Smith, 1995; Scheirer and Macdonald, 1995; Scheirer et al., 1996; Smith, 1988; Vogt and Smoot, 1984], and modification by post emplacement processes [Moore et al., 1989; Smoot and King, 1992]. Primary control of shape is by : (1) the tectonic setting [Batiza, 1982], (2) fracture pattern of the plate, (3) mantle heterogeneities (thermal and compositional) [e.g Davis and Karsten, 1986; Kincaid et al., 1996], (4) age and thickness of the lithosphere [e g Vogt, 1974], (5) chemical composition of the magma [e.g Batiza et al., 1989], (6) physical properties of the magma such as effusion rate and viscosity [e.g. Bonatti and Harrison, 1988], (7) shape, size and geometric relations of magma supply conduits, (8) availability of magma, and (9) post emplacement modification such as reef growth, wave truncation, and/or slope failure. Two tectonic environments which are responsible for the supply of mantle material to the oceanic crust are: (a) a plume influenced region which is anomalously hot, and thus producing low viscosity flows; and (b) a passive upwelling, non-plume, environment which produces higher viscosity flows from a cooler source, such as mid-ocean ridges or intraplate zones of weakness [Kincaid et al., 1996] Both of these environments may be near-axis and/or off-axis The terms "axis", "near-axis", "spreading center", "mid-ocean ridge" and "ridge" are used interchangeably to describe the elevated region on the Earth's surface, which is the tectonic boundary between two adjoining plates, and the region of mantle upwelling and formation of new oceanic lithosphere. 5

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1.2.1 Mid Atlantic Ridge (Slow Spreading Rate) Seamounts are commonly associated with volcanic process e s in an intraplate or near-axis setting Near axis seamount produ c tion is primarily controlled by spreading rate and magma flux [Alexander and Ma c donald, 1996 ; Scheirer et a/., 1996; Smith and Cann, 1993] In slow spreading environments (-25 mm yf1 full rate) such as the northern Mid Atlantic Ridge (MAR) seamounts are formed within the median valley floor and transported by large scale faulting to the ocean floor [Magde and Smith 1995; Smith and Cann, 1993] The region is dominated by axial rift valleys 30-45 km wide and 1-2 krn deep having an inner valley flo or b o und e d by n ormal faults tha t are hundreds of meters high [Macdonald, 1986]. The inner valley flo or is the main site of crustal accretion, where production of volcanoes and ridge s up t o several hundred meters h i gh takes place. This volcanism is proposed to originate from small pockets of melts rising through the lithosphere to the base of the asthenosphere, where they are pounded at a brittle/ductile boundary, possibly formed by cooling via hydrothermal circulation [Che n and Morgan, 1990], or being a level of neutral buoyancy [Smith and Cann, 1993]. These models call for each edifice and flow to be fed by a separate small magma bod y, whos e distribution is related to a distribution of magma b o die s with d e pth [Magde and Smi th 1995; Smith and Cann, 1992 ; 1993; Vogt, 1974] 1.2.2 East Pacific Rise (Fast Spreading Rate) Although the present day spreading rate is not at fast as this study area, work on seamount abundance's in the n e ar axi s zon e of the southern Pacific Nazca EPR, between 15 S and 19 S (up to 140 mm yr full rate, using the revised astr o nomically calibrated time scale, NUVEL-1A model [DeM e ts e t al., 1994]) [Scheirer et al., 1996], and north e rn Pacific Nazca EPR, between go N and 17 N (up to 112 mm yr"1 full rate ) [Sc heirer and Ma c donald, 1995] have been made Seamount production occurs within a narrow zone, 5 -6

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15 km from the axis, with significant growth only out to 25-60 km from the ridge crest [Alexander and Macdonald, 1996; Macdonald et al., 1993 ; Scheirer and Macdonald, 1995; Scheirer et al., 1996 ; Shen et al., 1993]. Scheirer et al. [1995] find that the greater abundance of seamounts is found on elevated and inflated regions of the northern EPR as opposed to areas with a smaller cross-sectional area. When comparing among seamount abundance's in various spreading rates and ridge morphology, Scheirer et al. [1995] find that on a gross scale, near-axis seamount abundance s increase with spreading rate and ridge morphology changes from a rifted valley to an axial high. 1.2.3 Intraplate Environments Intraplate seamount production may be found at local upwelling regions; possibly related to secondary convection rolls [Bonatti et al., 1977; Richter and Parsons, 1975; Searle et al., 1995]; mantle heterogeneities [Davis and Karsten, 1986; Schilling, 1985]; miniplumes [Shen et al., 1993]; and hotspots [Duncan and Richards, 1991; Epp, 1984 ; Liu 1996; Morgan, 1972; Pilger and Hands chul1Ulcher, 1981; Wilson, 1963a ; Wilson, 1963b]. Hotspots may have significant interaction with a near by ridge and lead to channeling of material [Fontignie and Schilling, 1991; Haase et al., 1996; Karsten and Delaney, 1989; Kincaid et al., 1996; Magde and Smith, 1995; Oknl and Cazenave 1985; Olson and Nam, 1986; Schilling, 1985; Schilling, 1991; Schilling et al. 1985a; Schilling et al., 1985b] Points of weakness along which magma is able to penetrate the lithosphere, such as those formed by fracture zones [Clark and Dymond, 1977; McNutt et al., 1989], diffuse regional extension [Jackson and Shaw, 1975; Sandwell et al., 1995; Searle et al., 1995; Turcotte and Oxburgh, 1978; Winterer and Sandwell, 1987] thermal contraction normal to spreading direction [Turcotte and Oxburgh, 1978] or subduction zones [Sandwell et al., 1995], are also areas favorable for seamount formation 7

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1.3 Formation of the Easter Seamount Chain The chain of separate and coalesced seamounts in the study area has been termed in the literature as the Easter Fracture Zone, the Salas y Gomez Ridge, the Easter Hot Line, the Easter Volcanic Chain, and the Easter Seamount Chain (ESC), which reflect the various models proposed to explain their origin [Hagen et al., 1990]. The mode of formation is under current debate, but it is certain that the volcanic constructs describe a complex interaction of the oceanic crust with the mantle The proposed models are based on either geochemical signals from dredged and exposed rock, seismic studies, side-scan interpretation, gravity, magnetics, or altimetry or a combination of these observations. 1be models include "Hotspot", "Leaky Fracture Zone", "Hot Line", and "Diffuse Extension''. 1.3.1 Tectonic Setting The study area is approximately a rectangle from the EPR to Salas y Gomez Island (SYG) between 25-28S and l13-104W, an area of roughly 243,400 krn2 (black envelope in Figure 1). The area lies entirely within the Nazca plate, having its western boundary as the portion of the EPR between the Easter microplate (EMP) and the Juan Fernandez microplate (JFMP) (Figure 2). It is part of an area of anomalously shallow topography (ESC) which extends eastward to the Nazca ridge, within -1000 krn off the coast of South America and the Peru-Chile trench. The ESC is a broad feature roughly 3000 krn long, extending from the EPR to the Nazca ridge trending at -085 [Liu, 1996]. The rate of crustal formation of this region is close to the fastest on Earth [Naar and Hey, 1989a]. Present day Nazca-Pacific relative spreading (at 27 S) is about 151 mm yr"1 full rate [DeMets et al., 1994; Hey et al., 1995] (Figure 1). The Nazca-hotspot absolute spreading direction is 085, calculated from the overall trend of the chain combined with the trend of the Galapagos and Juan Fernandez Islands [Liu, 1996] Due to low age resolution of those chains Liu [ 1996] was unable to calculate a rate. The absolute spreading direction 8

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of the Nazca plate (at 27 S) is different than the previous estimation of 123 based on the revised NNR-NUVEL1 global hotspot model [Gripp 1994]. Gripp [1994] calculated this vector by combining the Nazca-Pacific and Pacific-Hotspot spreading vectors, to a resultant Nazca-Hotspot vector. The relative and absolute spread i ng direction and rate, where available, are tabulated for a location at 27S,l08W, on the Nazca plate (see Table 1). The study area includes seafloor from zero age to anomaly 5 age (-9.8 Ma) [Cande and Kent, 1995; Liu, 1996] (isochrons seen as light gray stripes in Figure 3) Table 1. Relative and absolute plate velocities at 27S, 108W from different models. Euler Vector Motion Vector Source Latitude Longitude velocity Azimuth Rate Plate ON OE deg/ma deg mm yr"1 Model Reference nz-pa 55.578 -90.096 1.4222 100.1 157.2 NUVEL-1 DeMets, 1990 nz-pa 55.578 -90.096 1 .3599 100. 1 150.3 NUVEL-1Ab DeMets, 1994 nz-hs 45. 7 -90. 2 0.46 102.8 49.3 NN2-NUVEL1c Gripp, 1990 nz-hs 47.129 51.306 0 .3265 123.4 15 8 NNR-NUVEL1c Gripp, 1994 nz-hs 85.900 171.400 N/A 085.5 N/A Nazca best fitd Plate abbreviations: nz, Nazca; pa, Pacific; hs, Hotspot. N/ A, not available. a Full rate b New astronomically calibrated rates Liu, 1996c c NN2 and the revised NNR, nz-pc absolute rate is calculated from pa-hs and pa-nz rates. d Calculated for the Nazca plate from three chain lineations. 1.3.2 Relation to the Easter Microplate Three microplates currently exist along the fast spreading EPR: the Galapagos (1 N), Easter (25S) and Juan Fernandez (33S) microplates. All three have formed in the last 5 Ma [Lonsdale, 1989; Searle et al. 1993]. Herron s [1972] discovery of the Juan 9

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Figure 3. Seafloor age isochrons and interpreted young lava flows. Light gray stippled lines are age isochrons along with their magnetic anomaly Spreading axis, failed propagators, fractures zone (FZ), and pseudofau1ts are represented by thin black lines. Dark gray regions are areas of high reflectivity, interpreted from GLORI-B side-scan imagery [isochrons and flows are based on Liu, 1996]. Named volcanic features are included based on published works [Danobeitia et al., 1995; Hagen et al., 1990; Stoffers et al., 1994] Abbreviations: vole, volcanic; Smt, seamount; SyG, Salas y Gomez; and lsi, Island.

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..... ..... -26 -28 2a i 2a -114 -112 4a 5 4 4a -110 -108 -106 -104

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Fernandez (JFMP) and Easter (EMP) microplates (Figure 2), based on a ring of earthquake epicenters, has lead to detailed study of microplate kinematics and evolution [Handschumacher et al., 1981; Hey et al., 1995; Hey et al., 1985; Larson et al., 1992; Naar and Hey, 1991; Rusby, 1992; Schouten et al., 1993; Searle et al., 1993; Searle et al., 1989]. The two southern microplates have similar tectonic pattern and evolution [Bird and Naar, 1994; Searle et al., 1993], and may have initially originated from an overlapping spreading centers [Macdonald et al., 1991; Searle et al., 1989] between the Pacific and Nazca plates. Side-scan interpretation show that the EMP has formed in the past 5 Ma and has subsequently rotated in a clockwise fashion an average of 17 Ma described by a "roller bearing" i.e the microplate edges are been rotated rigidly by the motion of the major plates [Larson et al., 1992; Schouten et al., 1993 ; Searle et al., 1993]. It is under debate whether the proximity of the Easter hotspot has a significant effect on microplate kinematics and development. Hagen et al. [1990] conclude that a hotspot on the EPR 4.5 Ma may have initiated the rift propagation that created the microplate. Handschumacher et al [1981] speculated that there may be a genetic relationship between the EMP and the ESC. Details of the EMP formation and a history of previous work is w ell documented in the literature [Naar and Hey, 1989a,1991; Rusby, 1992; Searle et al., 1993]. 1.3.3 Seamount Ridges along the ESC Throughout the study area are regions of young lava flows on top of older seafloor (Figure 3), based on interpretation of GLORI-B side-scan and magnetic anomalies [Hagen et al., 1990; Liu, 1996; Naar et al., 1993a ; Stoffers et al., 1994]. In detail the volcanic construction appears complicated, but in general several large volcanic chains dominate. These large volcanic ridges have trend s 5-15 oblique to relative plate motion (Figure 3), and are aligned in a dextral en-echelon pattern The ridges are broad regions of elevated topography, 1-3 lcm in height, 200 500 lcm long, and less than 80 lcm wide [Liu, 1996]. 12

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Figure 4. Shaded observed bathymetry of the ESC, from GLORI-B processed bathymetry data Gray scale is in kilometers in the upper left comer of figure, 1000 meters contours, from light (shallow) to dark (deep) Average seafloor depth in the study area is 3200 meters. The data is compiled into a grid of 007 by .007 degrees from SeaBeam2000, GLORI-B, SeaMARC II, and ETOP05 data sets [Liu and Naar, 1996b; Liu et al. 1994]. White outline is of study area envelope, black lines are portions of the western rift of the Easter microplate, and location of Easter Island (star) and Salas y Gomez Island (triangle) are included for reference, consistent with the all figures

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0 \0 ('I I 14 0 00 ('I I 0 ....... I 0 \0 0 ....... I 0 00 0 ...... I 0 _... ....... I 0 ('I ....... I 0 """ -....... I

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They are separated from each other by regions of lower topography and smaller volcanic e<;lifices. Based on side scan imagery interpretation some of the seamounts and lava flows appear to be associated with these ridges (Figure 4) However most of the fresh volcanism, having light return s on the side scan sonar imagery are clearly not associated with the larger chains. This suggests that the large chains are of an older origin and are not part of the younger and intens e volcanic episode 1.3.4 Hotspot Model Hotspots are upwellings of primordial material from the deep mantle and are proposed to be relatively stationary with respect to each other and the deep mantle [Duncan and Richards, 1991; Morgan 1971; Wilson, 1963a] Morgan [1971; 1972] was the first to propose the formation of the Easter-Salas y Gomez Island seamount chain by a hotspot fixed relative to the mantle at Easter Island The location and structure of such a hotspot is currently under debate, but it is thought to be located somewhere near Easter Island or Salas y Gomez Island, thus providing a source for much of th e ma g mati s m [Fontignie and Schilling, 1991 ; Liu et al., 1995; Maia et al. 1994 ; O'Conner et al., 1995 ; Okal and Cazenave, 1985 ; Schilling et al. 1985a]. Based on estimation of low m a gma production rates and a low degree of partial melting it is thought that this i s a weaker and cooler hotspot than that which has formed the Galapago s or Hawaiian-Emperor seamount chains [Haase and Devey 1996; Schilling 1991 ]. Publi s hed 44 Ar/39 Ar and whole rock KJ Ar age data show that lava ages generally increase to the east between the Nazca Ridge and the western end of Salas y Gomez Island chain strengthening the theory that this portion of the ESC is formed by plate motion over a plume, the manner of which is still under debate [Haase et al., 1996; Liu, 1996; O'Conner et al 1995; Poreda et al. 1993b]. However, preliminary lava ages using 4 0Arfl9Ar, west of Salas y Gomez Island show no single linear trend Although, an age trend with zero age near the Ahu volcanic field and increasing ages 15

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to the east is seen [R. Duncan personal communication, 1996; Clark 1977; O'Conner, 1995; Liu, 1996]. Reconstruction of the Southeastern Pacific reveal that the Nazca and the Tuamotu ridges have a common origin that of a melting anomaly under the ancient Pacific-Faralon ridge, before 20 Ma [Handschumacher et al. 1981; Okal and Cazenave, 1985; Pilger and Handschumacher, 1981]. Dispersion of Raleigh waves over the Nazca ridge compares favorably with those obtained on the Tuamotu ridge, thus substantiating the hypothesis of a common source [Woodsand Okal, 1994] However, the Easter-Salas y Gomez-Islands chain, present only on the Nazca plate does not have a clear conjugate or mirror' chain on the Pacific plate [Pilger and Handschumacher, 1981] According to Okal and Cazenave [1985], after Pacific plate tectonic reorganization, about 25 Ma, the hotspot responsible for the formation of the ESC and the northern Tuamotus crossed the East Pacific Rise and is now under Salas y Gomez Island on the Nazca plate. The seamount chain of Oneo Henderson-Ducie-Crough were formed by a separate hotspot. This hotspot is thought to be currently located a few hundred kilometers south of the Easter microplate [ Okal and Cazenave, 1985; Searle et al., 1995]. Both seamount lineaments intersect the rise axis at the location of the Easter microplate A detailed history of Southeast Pacific tectonic reconstruction can be found elsewhere [Lonsdale, 1989; Rusby, 1992]. 1.3.4.1 Simple Hotspot The simple hotspot hypothesis predicts a systematic increase in age of volcanism with distance from the hotspot [Morgan, 1972], and increasing sediment thickness overlying volcanic flows Also a plume like geochemical signal is expected based on this model. The chain of seamounts would then record the absolute motion of the Nazca plate relative to the hotspot reference frame Pilger and Handschumacher [1981] developed a simple hotspot model for the Nazca Ridge and the ESC, which placed the hotspot 200 km 16

PAGE 29

west of Easter Island, on the East rift of the Easter microplate. They agreed with earlier ideas that the Nazca Ridge and the Tuamotu were formed by an on-ridge hotspot but that the Salas y GomezEaster Island chain was formed entirely by an intraplate hotspot. Fitting their model to a unified Pacific-Nazca-Hotspot model had kinematic problems, mainly because of the bend of the Tuamotu Ridge occurred 55 Ma, and that of the Hawaii Emperor Chain was given at 42 43 Ma. Pilger and Handschumacher [1981] proposed an alternative model which placed the hotspot just east of Salas y Gomez, which would have difficulties explaining the presence of Easter Island, unless there was channeled flow to the west, toward the ridge [Hagen et al., 1990 ; Morgan, 1978]. 1.3.4.2 Hotspot-Ridge Interaction Based mainly on geochemical observations, interaction between the Easter hotspot and the East Rift of the Easter microplate has been proposed, through channeling of plume material to the ridge (Figure 5a) [Fontignie and Schilling, 1991; Fretzdorff et al., 1993; Haase and Devey, 1996; Haase et al., 1996; Haase et al. 1993; Hey et al., 1985 ; Kincaid et al., 1996; O'Conner et al., 1995; Poredn et al., 1993a ; Schilling, 1991; Schilling et al. 1985a]. Schilling et al. [1985] report that dredge rock samples from the East Rift of the Easter microplate (between 22S and 29S) are richer in and show higher La/Sm than the West Rift limb of the Easter microplate, culminating at 27S. Suggesting that a plume is possibly present to the east of the EPR at this latitude. Schilling and his co-workers find that Pb [Hanan and Schilling, 1989], 87Sr/86Sr [Fontignie and Schilling, 1991], and 3HetHe [Porecla et al., 1993b] from the East Rift versus those from the West Rift support a binary mixing model of plume and ridge material to the East Rift The .. migrating ridge hotspot source" model put forth by Schilling [1985;1991], demands focusing of magma from the plume to the migrating spreading ax i s and possible interaction between the hotspot and existing lines of crustal weakness. This would explain a volcanic gap between the 17

PAGE 30

EPR and the Ahu field, a "shot gun"-type distribution of volcanism and a wide, ridge perpendicular, zone of contemporaneous volcanism Other geochemical studies [Fre tzdorjf et al., 1993; Haase and Devey, 1996; Haase et al., 1996; Haase et al., 1993] show enriched to strongly depleted REE patterns from dredges samples west of Easter Island, which suggest a mixing of melt from both normal Mid-Ocean Ridge Basalt (N MORB) and plume source As seen on a bathymetric chart (Figure 4) there is a -150 km volcanic gap between the Ahu volcanic [Hagen eta!., 1990] and the East Rift of the Easter microplate, explained by Haase et al. [1996] as a counterflow of MORB material to the plume and bi-directional mixing of material. 1.3.4.3 Hybrid Hotspot Models Another modification of the hotspot mode is the "sheared plume" model for the formation of en-echelon hotspot trails (figure 5b) This model predicts that the volcanic expression of rising hotspot "blobs" is related to the distance from the ridge, and the relative motion between the lithosphere, mantle, and the plume source [lhinger, 1995; Liu, 1996]. Such a model has been proposed for the formation of the ESC based on observations made from GLORIB and SeaBeam2000 bathymetry. The model also relies on preliminary results of age data collected along the chain, during the Gloria Leg 7 cruise [Liu, 1996; Liu et al 1995] The model suggest that "plumlets of primordial mantle material rise to the base of the lithosphere, crossing a shear zone, and are stretched into "football" shaped lenses. Liu [1996] suggests that the current constructional configuration of the ESC is caused by the shearing of the mantle and lithosphere in the same direction as relative plate motion and a relative migration of the Easter hotspot. The overall pattern of the ESC is dextral and en-echelon, while the trend of individual chains is parallel to the relative plate motion, as predicted by this model. 18

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A Figure 5. Cartoons of models proposed for the formation of the Easter Seamount chain Figures b-d are modified from Scheirer et al. [1996], their figure 17. (a) Plume channeling Om material to the ridge Based on Schilling [1991]. (b) Sheared blobs fed by an unstable layer at depth, having a different horizontal flow than the asthenosphere Based on Liu [1996] and Ihinger [1995]. (Continued on next page) 19

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Figure 5 (continued) \ c (c) Diffuse extension of the lithosphere. Volcanism is predicted to occur along the crest of topographic highs. Based on Sandwell eta/. [1995]. Hot line or ridge perpendicular secondary convection Volcanism is predicted to occur along the troughs of topographic highs. Based on Bonatti and Harrison [1976] and Richter and Parsons [1975]. 20

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1.3.5 Leaky Fracture Zone Sparse volcanic age dates which do not show a clear linear age progression with distance from the axis, along with evidence of contemporaneous volcanism over the length of the chain, led Clark and Dayamond [ 1977] to propose a model which could explain their fmdings. A fracture zone is indicated by offset of magnetic anomalies on either side of the ESC (125W,24S to 108W 27S and offsetting the Mendoza Rise at 950W) [Handschumacher, 1976; Herron, 1972a]. Clark and Dymond [1977] proposed that this is a "leaky" fracture zone and is responsible for the formation of the Salas y Gomez chain According to this model, the ESC formed in response to large-scale plate re-orientation of the spreading centers from the NNW trend of the Mendoza Rise to the ENE trend of the EPR, along with differential spreading rate on either side of the Easter Fracture Zone This model can accommodate contemporaneous volcanism along the chain, and the slight age offset between Easter and Salas y Gomez Islands Geochemical findings indicate that magmas at Salas y Gomez and Easter Island formed from magmas which equilibrated at different pressure, consistent with a model of volcanism from the melt of magma which segregated at the base of a progressively thickening lithosphere Results from dispersion of Rayleigh waves along the ESC, reveal that the there is no thick crust along the ESC and abnormally th i ck crust along the Nazca Ridge [Woods and Okal, 1994]. These investigators conclude that the ESC may be a result of a leaky fracture zone not a simple hotspot trail. Similarly, a fracture zone is thought to interact with a hotspot in the Marquesas, resulting in intraplate volcanism preferentially orientated along the fracture zone [McNutt et al. 1989]. This could occur in a region in which the plume is not strong enough to penetrate the older, cooler and thicker lithosphere but able to travel along zones of weakness such as the fracture zone. 21

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Magnetic anomalies are poorly defined in the area of Easter Island, although an offset of anomalies is apparent [Herron, 1972b; Liu, 1996; Naar and Hey, 1989b]. However, the SOEST Fracture Zone [Hey et al., 1995] lays south of the ESC, does not seem to be directly associated with broad volcanism and does not appear to extend much further than anomaly 3a, possibly due to previous non-transform offsets of the superfast EPR. 1.3.6 Diffuse Extension Model Based on satellite altimeter measurements of marine gravity, it is revealed that wide (100 to 200 km) wavelength lineations exist over a large area of the Pacific plate, and are oriented approximately in the direction of absolute plate motion (Figure 5c) [Sandwell et al., 1995]. The diffuse N-S extension (of the lithosphere) model, would predict lineated, 50-70 km wide, zones of volcanism in the trough of the more prominent gravity lineations, explaining many features in the Pacific [Winterer and Sandwell, 1987]. Potential problems with this model are that: (a) lack of evidence for extensional faults parallel to the ridges; and (b) significant extension has not been necessary in plate reconstruction models (and the extension model requires greater than 10% stretching of the lithosphere). 1.3. 7 Hot Line Other investigators also observed that volcanism seemed to be young along the entire length of the chain, and of a plume like source, but noted that it is aligned in a direction perpendicular to the spreading axis (Figure 5d). Building on the hypothesis that secondary convective rolls may occur parallel to the direction of spreading during mantle convection [Richter and Parsons, 1975], Bonatti et al. [1977] suggested that convective rolls produce "hot lines" such as the ESC. Based on KJ Ar age dating of highly altered samples, these investigators found that volcanism along the chain could not have formed from a single, fixed, hotspot beneath Easter Island Also, they reason, the ESC could not 22

PAGE 35

be a result of material passively rising through a fracture zone, which is generally characterized by little volcanism Rather, evidence of intense volcanism and its wide spread occurrence suggest that the ESC is possibly the result of mantle activity occurring along the rising limbs of adjacent Richter convective rolls [Bonatti and Harrison, 1976] Gravity study along the chain does not entirely exclude a convective origin for the chain either [Maia et al., 1994; Maia arul Diament, 1991]. This model although allowing for intermittent volcanism, requires that volcanism occur along topographic highs ; something that with higher bathymetry resolution studies [Naar et al., 1993a] and satellite altimeter studies [Sandwell et al., 1995] has not been observed. 1.4 Rationale for Study Seamounts may form in a variety of tectonic environments and causes. Likewise, a variety of models have been proposed for the formation of the ESC. It is the objective of this study to eliminate or refine previous models, or propose a new model for the formation of the chain. This may be possible based on the results of a shape and size distribution analysis and comparison of seamount character to those from studies in different settings The present study is in a unique geological setting of a superfast, intraplate environment, influenced by an anomalously hot region. Here the abundance, size distribution and shape character of a complex region is quantitatively examined. The size distribution is analyzed through the use of previous methods [Smith and Jordan 1987], and a modified method 23

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CHAPTER 2: SEAMOUNT SHAPE AND SIZE DISTRIBUTION 2.1 Introduction As in previous morphological studies of Pacific seamounts [Batiza 1982 ; Smith, 1988], most of the variation in shape can be described by two variables flatness (ratio of summit diameters to basal diameter) and summit height (Figure 6) Seamount flatness is a primary constructional form, resulting from caldera collapse, infilling of summit depressions with lava flows, or mass wasting and other post-emplacement modifications, such as wave cutting, slope failure and carbonate reef growth [Batiza, 1982] The initial profile is controlled by geological factors such as conduit geometry magma rheology, effusion rate, and magma availability [Fomari et al., 1987a]. The limitation of volume and depth and/or temperature of the magma source play a major rol e in s eamount morphology [Smith and Cann, 1992; Vogt, 1974]. A h o tter source produces less viscous lava, resulting in lower slopes and greater flow lengths, creating shield morphologies [Bonatti and Harrison, 1988; Kin caid et al., 1996 ; Morgan et al., 1995] While a cooler source produces higher slopes and flattened morph o logies In order to make inferences about the physical properties of the erupted lava a comprehensive and quantitative study of seamount shape characteri s tics has been carried out on the seamounts of the ESC. 2.2 Data Set Side-scan and swath bathymetry were collected during GLORIA Legs 05 and 06, using the new GLORI-B 6.5 kHz side-looking sonar [Somers and Hugget, 1993] and 24

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Flattened cone -100 times vertical exaggeration 0.6 Q,__ 0.2 0.0 Pointy cone 200 600 1000 1400 Seamount Height (m) Figure 6. Cartoon diagram relating the two principal components of variability. Seamounts at the bottom are pointy (flatness of 0.0) and those at the top are flattened (flatness of 0.6). The bases of the seamounts are proportional to their height bases on the relationship in Figure 1 Oa. There is a 100 times vertical exaggeration. This diagram is based on Figure 6 from Smith [1988] Also shown schematically variables measured for all seamounts: d, minimum summit diameter, D, minimum basal diameter; h, maximum height. Flatness is the ration of diD 25

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SeaBeam2000 multibeam bathymetry and acoustic intensity imagery systems in the Spring of 1993 [Liu and Naar, 1996a; Liu et al., 1994 ; Naar et al., 1993a; Naar et al., 1993b] The GLORI-B system measures the phase difference and the arrival time of the returning echoes, to detennine depth and location of scattering points across the swath. To provide higher resolution the GLORI-B data were further processed and merged with SeaBeam2000 bathymetry [Liu and Naar 1996c] (Figure 4) and GLORI B side-scan merged with SeaBeam2000 imagery data [Liu and Naar 1996b] 2 3 Method Used The bathymetry data are contoured at 100m depth intervals, and plotted in standard Mercator projection (11.68 inches/d e gree of latitude) to co-register with the GLOLRI-B side scan mosaics ( -1: 334,000 at 27S) used to make mosaics during leg 5 Only seamounts greater than 200 m in height and with approximately equant shapes (ratio of maximum to minimum basal diameter less than two) are used in this study. Exclusion of seamount with aspect ratios greater than two was done for consistency with other studies [Magde and Smith, 1995; Scheirer and Macdonald, 1995; Scheirer et al., 1996; Smith and Cann, 1992] and to reduce the possibility of including fault-controlled flows. Exclusion of seamount with heights less than 200 m was necessary due to the resolution of the GLOLRI-B system Each seamount is approximated as a truncated, right conical-ellipse and the position of its center, maximum and minimum basal diameter (D), maximum and minimum summit diameter (d ) are recorded (see Figure 5) Individual seamounts are identified by visual inspection, and their basal outlines digitized (Figure 7) The base of each seamount is defined as a sharp break in slope from the average depth of the region (by inspection) surrounding the seamount (to the nearest 100 m contour), and continuing along the break in slope until the seamount is circumscribed. Each seamount is extracted ("cookie-cut") from the gridded bathymetry data after a regional 26

PAGE 39

seafloor subsidence trend is removed The height (h) of the seamount is calculated as the difference between the depth of its base and the shallowest point within the seamount's outline with a resolution of 10 m. Basal area, although a dependent variable on height and radius, was then collected independently by using the digitized outline and the gridded bathymetry flle at 0.003 by 0.003 degree grid. Volume was then calculated based on the sum of pixels making up the basal area and the height above each pixel in the dense bathymetry grid. In several locations, individual seamounts consist of overlapping volcanoes and volcanic ridges, making classification difficult. Because the overlapping represent a minor component of total volume those overlapping regions were included in the volume of both adjacent seamounts. Previous studies describing seamount shapes found it sufficient to approximate individual seamount edifices as regular truncated cones, for the purpose of approximating shape parameters [Bemis and Smith, 1993; Scheirer and Macdonald, 1995; Scheirer et al., 1996; Smith, 1988]. This study finds it necessary to approximate seamounts as regular elliptical cones, and find that use of this method results in a close estimation to their actual volume and basal area (a comparison of the two basal outlines is seen Figure 8) There is a slight under estimation of seamount volumes using this method, however it a linear relationship across all volume sizes (a comparison of actual versus approximate seamount volume is shown in Figure 9). The ellipses give an adequate representation of the basal area, useful in graphical presentation and estimation of shape parameters (Figure 10). Based on the dimensions of these simplified elliptical cones, the flatness, defmed as the ratio of minimum summit diameter to minimum basal diameter (f = diD), the aspect ratio, the direction of maximum basal diameter, the flank slope (= arctan(2h/(D-d)), and the 27

PAGE 40

Figure 7. Actual basal outlines of seamounts. Basal outlines of 383 seamount used in this study. and digitized from bathymetry data These outlines are used as "cookie cutters" to extract maximum height. basal and summit area. and total volume from the 0 003 by 0 003 degree data set The location of Easter Island (star). Salas y Gomez Island (triangle), the ridge axis (black line) and the study area envelope (thick black line) are shown for reference.

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---0 \0 N I 0 0 ... 29 0 0 v 0 I \o 0 I 0 00 0 I 0 pS 0 0 0 0 p 0 os:D 0 oo 0 00 N I 0 I

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-lOT 04' -106 56' -106 48' -26 48' -1.0 -2 0 -26 56' -3 0 -4.0 Figure 8. Shaded bathymetry plot of Getu Seamount. This diagram illu s trates the u s e of regular truncated elliptical cones to approximate seamount s h a pe This is a cont o ured shaded plot of Getu Seamount ( s eamount reference number 2 8 0, APPENDIX 1 and 2 ) with scale in kilometers below sea l evel, contoured at 50 m interval. It is 2410 meters high flatness of 0.02, and slope of 11. Black thick lines approximate base as regular ellip s e, lighter thick line is the actual basal out line digitized from cont our plots (see Figure 7). 30

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6000 ,....._ 4500 VapproxN measured = 0.74 (<'\ g 0 r2 = 0 .93 E ::J 0 > 3000 cu E ;;: 0 .... c. c. < 1500 0 0 1500 3000 4500 6000 Measured Volume (lan3) Figure 9 Relationship between approximate seamount volume versus actual seamount volume A slight underestimation of seamount volume, when approximated as regular elliptical cone. 31

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Figure 10. Simplified basal outline of seamounts with heights over 200 meters Outlines are overlaid on observed bathymetry (see Figure 4 ) Basal outlines are approximated as regular ellipses, with lengths and orientation of the long and short axis trend as parameters, they are scaled to map scale There are 383 seamounts with heights greater than 200 m and aspect ration less than 2 See text for methodology of basal outline determination, and Appendix I for detailed tabulation of shape parameters All subsequent plots of the entire study area are at the same scale, position on the page, and contain the simplified basal outlines of 383 seamounts used in this study

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0 \0 ('I I 33 0 00 ('I I 0 ....... I 0 \0 0 ....... I 0 00 0 ....... I 0 ....... ....... I 'N ....... ....... ....... ....... I

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cross-sectional area along the minimum basal diameter are estimated and tabulated for each individual seamount (Appendix 1). 2.4 Shape Characteristics In order to evaluate the components that are responsible for seamount shape variability statistics have been compiled for individual seamounts. There are a total of 553 seamounts in the height range of 200-3300 m. The population is reduced to 383 seamounts by eliminating those with aspects ratios more than 2, (summarized in Table 2). Their morphology is variable and complex (Figure 11), thus determination of flatness and flank slope is based on the seamount approximation as a truncated elliptical cone. Height is plotted against six seamount parameters; basal radius, summit radius, volume, crosssectional area, flatness and slope, in order to evaluate which parameters are correlated and can be used to best describe this population (Figure 12) Orientation of maximum basal diameter and their lengths are tabulated as well. than 200 m and aspect ratios greater than 2 Table 2. Statistical Summery of 383 seamounts. Height Basal Slope3 Flatness3 Volume Cross-hlrmio m Areac deg km3 sectional aread km2 km2 Mean 640 174.6 7.6 0.13 160 7.3 .25 Std. dev 540 378.9 3.8 0.10 480 15.9 .01 Minirnwn 200 4.6 1.7 0.01 1 0.3 .06 value Maximwn 3300 3757.4 22.0 0.57 5340 31.8 .61 value Only considered seamounts with heights greater than 200 m, and aspect ratio less than 2 b Measured from the average seafloor depth surrounding each seamount to its shallowest extent. c Determined by digitizing the base of each seamount by inspection and extracting the data from the gridded GLORI-B bathymetry. d Based on approximation of the seamount as a regular truncated elliptical cone 34

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0 -500 -1000 E -.c ..... c. -1500 Q) 0 -2000 -2500 -3000 0 10 20 30 40 50 Basal Diameter (km) Figure 11. Plot of the profile along the minimum basal diameter of the 12 largest seamounts. The linear-linear plot of seamount depths and their minimum basal diameter illustrates their complex summit morphology and slope similarity. 35

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Figure 12. Correlation between six seamount shape properties and seamount height. 383 data points in each plot. There are 383 circles in each plot, representing seamounts with heights greater than 200 m and aspect ration less than 2 (see text) (a) Basal radius plotted against seamount height. Relationship is linear with black line representing least-squares fit, with r2 of 0.80. The average ration of h/rmin is 0.25.01 (see Table 2). (b) Summit radius plotted against seamount height. There is no relationship between the height and summit radius. (c) Volume plotted against seamount height. Relationship is a third order polynomial with of 0.83 The volume of each seamounts approximates that of a right circular ellipse, having a cubic relationship with basal radius (d) Cross-sectional area plotted against seamount height Relationship is a power fit with correlation of coefficient 0 90. (e) Flatness plotted against seamount height. 0 is a pointy cone and above 0.2 is a flattened-dome. Notice high variability for seamounts with heights less than 1200 m. (f) Slope plotted against seamount height. As in flatness relationship, there is much variability for seamount with heights less than 1200 m.

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30 Linear OA ] f(x)=7 .16xto-3 x X 0 _.. 20 (r2 = 0 .80, N = 383/383) 0 en ::s .... 8 0 "0 r: 10 ";! en cu eel 0 12 g B en ::s 8 "'" --e e 4 ::s Cfl 0 6000 Polynomial oc 4000 ] f(x)=l.06xto-7 X x3 <-l= 0 83, N = 383/383) _.. e 2000 0 ::s 0 -0 > 0 0 200 700 1200 1700 2200 2700 3200 Seamount height (m) (Continued on next page) 37

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Figure 12 (Continued) Power f(x) = 1.64 x 104 x X 1.93 = 0 90, N = 383/383) 0 c; 80 c: 0 = 40 (.) 0 (I) I (I) (I) 0 0 '"' u 0 .6 0 E 0 0.5 (I) 0.4 (I) 0 5 0 3 (IS c 0.2 0.1 0 0 F 30 0 -0 CIA) .g 20 '-" 0 c.. oo o EIO 0 (I) 0 00 0 Co 8 0 0 200 700 1200 1700 2200 2700 3200 Seamount height (m) 38

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2.4.1 Orientation of Basal Diameter Analysis of the orientation of the major axis, of the seamount approximated as an ellipse, shows that there is a strong alignment of smaller seamounts to the north (Figure 13) However when plotting orientation of major axis based on cumulative axis length, it can be seen that there is a larger variability in orientation but an average orientation of 80 Comparing this orientation with that of relative plate motion (100)[DeMets et al. 1994], motion of the Nazca plate relative to the hotspot (85 ) [Liu, 1996], it can be see that direction of absolute plate motion is closest to the average trend of the individual seamount's axis of elongation 2.4.2 Height to Radius Seamount height versus minimum basal radius is well fit by a linear regression (Figure 12a), with a correlation coefficient of 0 .80. The 383 sample mean of h/rmio is 0.25. 0 1, consistent with results from other studies of about 0 .21 [e g. Smith, 1988]. By contrast, no correlation exists between height and summit radius (Figure 12b) The sample mean of the ratio of height to average summit radius is 1. 74 with a standard deviation of 2 18 The large standard deviation indicates that the data are highly scattered, and a clear relationship is either complicated or does not exist. 2.4.3 Volume Seamounts can be approximated as right circular cones, and their volume approximated using a simple model: V=a(2D)31t/3, where V is volume, D basal diameter and a a constant based on the linear relationship between h and d (Figure 12a). Volume was collected independently of maximum height. The volume of each individual seamount 39

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125 100 75 0 50 ;a ] 25 .&;) 0 e 25 e -:; 50 75 c :E 0 N 100 125 N s Mean orientation (80) Absolute plate E motion (85) Relative plate motion (1 00) Figure 13. Orientation of maximum basal diameter. The cumulative length of the maximum basal diameters in each 2 bin is plotted versus trend direction of the axis of elongation (between 00 and 180 ) This gives greater weight to large diameters and suppresses the influence of the more numerous smaller diameter seamounts As well the nz-pc relative plate motion vector and the nz-hs plate motion vector are plotted on the same rose diagram from Table 1. 40

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was plotted against height in Figure 12c. A third order polynomial was fit to the data, with a correlation coefficient of 0 83. 2.4.3.1 Seamounts' Contribution to the Crust The few large seamounts contribute to the majority of the volcanic volume in the area Over 50% of the total volume of seamounts used in this study (383 seamounts over 200m in height) is made up by the 14 largest seamounts and the remaining volume by the 369 smaller seamounts (Figure 14). A total of 61,000 km3 is added to the crust by the 383 seamounts over 200m. Assuming a uniform crustal thickness of 6 km (Chen, 1992) this represents 4 2% of the total crustal volume over the 243,00 krn2 study area The seamount basal area cover 67 000 krn2 or 27% of the seafloor Tills is significantly greater than the fmdings in the near axial zone of the N-EPR (8N-17N), of -6% of the area and -0. 3% of the volume [Scheirer and Macdonald, 1995] This is an anomalous region of the seafloor, representing an area of very active volcanism. 2.4.4 Cross-sectional Area The cross-sectional area of each seamount is approximated as a trapezoid, using the minimum basal diameter as the base, the minimum summit diameter as the top and the height from the base to its truncated summit (which may not be its maximum height) Cross-sectional area is plotted against height (Figure 12d) Using minimum basal diameter greatly reduces the influence of overlapping seamounts, and thus is a valuable seamount parameter The data are fit by a power law, with a correlation coefficient of 0.90. The agreement of cross-sectional area with the results of volume indicate that the volume measurements are not biased by overlapping geometries. 41

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100 60000 90 50000 -. 80 ('I") e ] ::I 70 '-" 0 40000 > E 8 60 ::I 6At/l 0 > :e 50 30000 100 ::j: (.) 40 > A ::: :e .o 6 .:. 75 .. A 20000 30 A ::I > E 4 50 -A ..... ::I 20 (.) 6 25 10000 ::I 'E 0 10 ::I 100 200 300 u 0 0 0 10 20 30 40 Seamount rank (1-383) Figure 14 Seamounts' volume contribution to the crust. Cumulative seamount volume versus the rank of the 40 largest seamounts along the x-axis (1 the largest. 383 the smallest) and the second y-axis is the percentage of total volume (-64,000 km3). Inset is the entire data set of 383 seamounts. 50% of the total volume is found in the 12 largest seamounts, 90% of the total volume is found in the 100 largest seamounts. The few large seamounts contribute significantly more to the total volcanic construction than the many small ones. Assuming a uniform crustal thickness of 6 km [Chen 1992], the total volcanic construction represents 4.4% of the total volume of the crust 42

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2.4.5 Flatness and Slope Flamess (the ratio of minimum summit diameter to minimum basal diameter) is plotted against height in Figure 12e The fla tness varies from 0.01 (a pointy cone) to 0 57 (a flattened truncated cone) as illustrated in Figure 6. The mean flatness is 0 14 with a standard deviation of 0 10 Seamounts in the lower size ranges (200 to 1200 m) show a wider variability in flamess than larger one s and have corresponding flank slopes ranging between 5 and 25 (Figure 12f) The highest seamounts (heights greater than 1200 m) can be approximated as pointy cones (with the exception of Easter Island, perhaps due to wave truncation or because it is actually composed of three summit craters), and have a mean flatness of 0 03 with a standard deviation of 0 02. The typical shape of seamounts with heights greater than 1200 m seems to be a pointy cone (flatness 0.2 or less), a broad base, and slopes between 5 and go (Figure I Of) (e g bottom left seamount in Figure 6) Those seamounts with heights less than 1200 m show a greater range in flatness up to 0 57, a mixture of pointy and flat (pancake like) cros s -sectional profile s illustrated by the seamounts on the far left in Figure 6 The relationship between slope and flamess is less clear There is a variability of seamount slopes at all flamess ranges, however pointy seamounts seem to have mostly low slopes and flattened seamounts hav e mostly steep flanks The binned and cumulative frequency plot of seamount flatness (Figure 15) show that most seamounts have flatness less than 0.28, and their distribution varies over most size ranges (Figure 16). Similarly, the binned and cumulative frequency distribution of seamount flank slope (Figure 17) show that most seamounts have slopes less than 14 and that their spatial distribution is variable over most size ranges (Figure 18) 43

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2.5 Observed Shapes and Patterns The study area contains areas having different volcanic histories A detail investigation of two regions of roughly equal area but having different seamount shapes and abundance's is described (Figure 19). The Ahu volcanic field, area "A", is estimated to be approximately 0 age, based on side-scan intensity comparison with recently created crust near the EPR, and age data [Hagen et al., 1990] (Figure 20) The area has rough but low bathymetric features, comprising an area of about 2700 km2 [Stoffers et al., 1994] (Figure 21) There are several steep scarps and terraces A deep-towed television camera near 26 s. 111 'W imaged ... pillow lavas which frequently emerge from the sediment" [Stoffers et al., 1994]. 78% of the 37 seamounts within the Ahu volcanic field area have a pointy morphology with variable slopes (Figure 22) and no clear spatial distribution. The o lder area, area "B", is interpreted as a heavily sedimented area, and older section of the seafloor, based on side-scan intensity (Figure 23). The older area is dominated by a single large volcanic base and numerous small volcanic constructs over printing it (Figure 24). There are over 80 seamounts which fit the seamounts criteria of this study (Figure 25). In area "B" 95% of the 80 seamounts are pointy elliptical cones with variable slopes. The seamounts average basal area is much smaller than that of the seamounts of the Ahu volcanic field Perhaps many of the seamounts represent flank eruption of a much larger edifice The seamounts have a nearly even spatial distribution, whereas the Ahu seamounts are clustered within the boundaries of the fresh lava flows 44

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c 400 45 "0 Q) c E :0 350 40 (/) c (/) Q) ca 35 c >. 300 Q) E ca ;::: CD Mean = 0 13 +1-.005 30 C\1 6-250 0 CD median= .11 0 ... :s.: 25 .c u.. 200 0 CD ca > 20 (I) :0:::: .E ca 150 :; ... E 15 Q) ::I .0 () 100 ::;: E 1 0 ::I c ... : (ij 50 5 -0 :': ..... 0 0 0 "'t CX) C\1 co C\1 "'t CX) C\1 co "'t "'t co C\1 co co 0 0 ..... ..... 0 C\1 C\1 ("') ("') "'t "'t ll) &0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Flatness Bins Figure 15. Flatness frequency distribution Histogram of seamount flatness in 0 02 bins, for flatness values between 0 02 and 0.6 (black bars). Cumulative frequency of flatness, based on bin sizes for the seamount population Note an inflection point at approximately a flatness of 0.28, illustrated spatially in the next figure 45

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Figure 16. Flatness spatial distribution Distribution of seamount flatness based on the inflection point seen in the flatness frequency distribution, represented as filled basal outlines. Small seamount sizes have a large flatness range, large seamount sizes do not show flattened morphologies.

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--....___ --\o 0l I 0 00 0 0 oo a 0 0 0 0 o o 00 0l I 47 I \o 0 ........ I 0 00 0 I ........ I

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400 .-------------------70 350 300 >-g 250 CD ::J tr ._ cu 'S 200 E 150 ::J 0 100 50 0 c: co Q) E 00 0 -Mean = 7 6 +1-. 19 median = 6 65 N \0 00 ----Flank slope bins (degrees} 60 c: :0 Q) 0> Q) '0 C\1 .r:. 40 g Q) .... (1) .0 30 c: iii 0 20 10 0 Figure 17. Slope frequency distribution Histogram of seamount flatness in 1:' bins for slope values between 2 and 22 (black bars) Cumulative frequency of slopes, based on bin sizes for the seamount population Note an inflection point at approximately a slope of 12, illustrated spatially in the next figure 48

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Figure 18. Slope spatial distribution. Distribution of seamount flatness based on the inflection point seen in the slope frequency distribution, represented as filled basal outlines Small seamount sizes have a large slope range, large seamount sizes do not show high flank slopes

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---0 \0 C"' I 0 0 0 0 (). 50 00 C"' I 0 \0 0 ....... I 0 00 0 ....... I 0 C"' ....... ....... I ....... ....... I

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Figure 19. Location map of detailed study areas. Two areas are investigated in more detail in order to compare seamount shape parameters between areas having different side-scan intensity. Areas "A", Ahu volcanic field has high intensity, and area "B" has lower intensity over all.

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\o N I 52 0 00 N I 0 ....... I 0 \0 0 ....... I 0 00 0 ....... I 0 0 ....... ...... I -I

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-111 30' -111 00' -26 00' -26 30' -2T 00' -2T 30' -110 30' -uo o oo -109 30' 255 160 140 120 100 80 60 40 20 0 Figure 20. Side-scan intensity of Ahu volcanic field, area "A". Int e nsity from GLORI B side-scan and infilled with SeaBeam pseudo side-scan in some places (light gray "Band Aid") [Liu and Naar, 1996a; Liu et al 1993] The light regions are areas of high reflectivity, presumably representing areas of recent volcanism, and dark regions are areas of low reflectivity, presumably older and sedimented areas of the seafl o or. Dark areas surrounding shallow seamounts and between ship tracks are artifacts of the GLORI B system. Scale bar of gray scale (0-255), from dark (low reflectivity ) to light (highly reflective). 53

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111 30' -111 00 -110 30' -110 00' -109 30 -26 00' 1 0 -26 30' -1 -2 -27 00' -3 -4 -27 30' -5 Figure 21. Shad e d bathymetry of area "A" 200 m contours and 1000 m annotation Approximately 34,000 km2 region of the se at1oor (1.5 by 2 ) The area is relatively flat, dotted by many small seamounts (with heights le s s than 200 m), and 37 larger seamounts found at the eastern end of the region 54

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Figure 22 Shape distribution in area 11 A II. (a) Flatness spatial distribution (b) Slope spatial distribution There are 37 seamounts with heights greater than 200 m.

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56

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-los 30' -108 00' -27" 00' 27 30 -28 00 -28 30 -107 30' -lOT 00' 106 30' 255 160 140 120 100 80 60 40 20 0 Figure 23 Side-scan intensity of ar e a "B". An ar e a of mostly low reflectivity and older seafloor. Scale bar of gray scale (0-255), from dark (low reflectivity to light (high reflectivity). 57

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108" 30' -108 00' -lOT 30' -lOT 00' -106 30' -27" 00' 1 0 -27" 30' -1 -2 -28" 00' -3 -4 -5 Figure 24. Shaded bathymetry of area "B". 200m contours, and 1000 m annotation The area is dominated by 80 seamounts greater than 200 m in height spread over the region 58

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Figure 25 Shape distribution in area "B" (a) Flatness spatial distribution (b) Slope spatial distribution There are 80 seamounts with heights greater than 200 m

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-27" 30' -28 00' 0 .o -27" 30' -28 00' 60 flatness 0.60 0 28 0.00 C) B slope (de g ) 25 12 0

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2.6 Size Distribution Over 3000 volcanoes or circular volcanic structures are identified in the GLOLRI-B side-scan sonar data [Liu et al., 1993; Rappapon et al., 1994]. Many of these structures are lobate flows and mass wasting, similar to those observed along the Hawaiian Islands [Holocomb arul Searle, 1991; Moore et al., 1989]. Of these, 553 seamounts are in the height range of 200 to 3300 m, including 60 with heights greater than 1000 m. The size distribution of the seamounts is a characteristic of any portion of th e seafloor. As noted in chapter one, this study describes the seamount population on an an o malous portion of the seafloor These area has the combined effect of superfast spreading rates and the presence of a temperature anomaly, most likely a plume, leading to "intense" volcanism. Previous studies have described variations of seamount size distribution and overal l abundance's in different tectonic environments [Abers et al. 1988 ; Batiza, 1982 ; Bati za et al., 1989; Bemis and Smith, 1993; Fornari et al., 1987b; Kleinrock and Brooks, 1994; Magde and Smith, 1995; Scheirer and Macdonald, 1995; Scheirer et al., 1996; Smith and Cann 1993; Smith and Jordan, 1987]. Similar methods are applied to the analysis of this data set, and then the results are placed in context with fmdings from other regions. 2.6.1 Previous Method and Limitations To quantify the height distribution of seamounts, J o rdan e t al. [1987] and other studies [Abers et al., 1988; Batiza. 1982; Bemis arul Smith, 1993; Kl e inrock and Brooks, 1994; Scheirer et al., 1996 ; Smith and Jordan, 1988] considered the cumulative frequency of seamount heights. They interpret their data as a negative exponential distribution expressed as v(H)= where v(H) is the number of seamounts per unit area having height greater than H, v0 is the total number of seamounts p e r unit area, is the 61

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negative of the slope of the line fitting ln(v (H)) versus H, where individual seamount counts are grouped into size bins The reciprocal of yields a characteristic height of the seamount sample (Figure 26) Smith and Jordan [1987; 1988] found that the height frequency distribution is fit by the exponential cumulative frequency distribution for areas of "ordinary" Pacific seafloor, excluding major hotspot traces, large fracture zones, subduction zones, back-arc basins, and the entire western Pacific. They noted that the exponential model did not fit the cumulative frequency data for seamount volumes [Smith and Jordan 1987]. Their model used a maximum likelihood regression fit to the binned cumulative height frequency data, over a set height range and did not use bins that contain less than 10 seamount counts. When following this methodology the results from this population of seamounts compare reasonably with other areas. However, this study uses the linear least-squares regression to fit an exponential and a power curve to the height and volume cumulative frequency data, without binning. This method has the advantage that it uses all available data, and eliminates bias resulting from assigning arbitrary bin sizes (C. Barton personal communication, 1996). 2.6.2 Exponential-law Distribution Cumulative frequencies of seamount heights binned at 2 m, 50 m and 100 m bin sizes were fit by the maximum likelihood method of Smith and Jordan [1987], using the MATlab routine fiter, provided by D .K. Smith (personal communication, 1996) (Figure 25a-c, respectively). The results, summarized in Table 3, yield a W1 (characteristic height) of 431 and 435 meters for the bin sizes of 50 and 100m, over a size range of 2003300 m A similar treatment made by fitting an exponential curve to the cumulative height frequency distribution data, without binning, results in a W1 of 574 m (Figure 27a) This is 62

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done using a linear leas-squares regression fit to the cwnulative frequency data 1be maximwn likelihood estimator down-weights the importance of size bins which are not well constrained (having few counts) (D.S. Scheirer, personal communication, 1996). However, here the data is not binned, to increase resolution (C.C. Barton, personal communication, 1996) An single exponential fit to the cumulative volume frequency data, using the linear least-squares regression, results in a poor fit to the data (r of only 0.64) (Figure 27b), a power law fit is tested, and described in section 2.6.3.2. Table 3. Comparison of seamount distribution parameters Height range Bin w Yo Predicted # Actual# (m) size (m) (/1000 km2 ) for 243,000 in (m) km2 200 height ran e Same range 200-1000 50 299 2.8.15 348 323 200-1000 100 305 2.7.015 340 323 200-1000 200 322 2.7.015 352 323 Range maximized 200-3302 2 433 2.5.13 383 383 200-3300 50 431 2.5. 13 381 382 200-3300 100 435 2.5. 13 383 382 Equation v(H)= v0exp(-PH) is based on the exponential cumulative maximum likelihood fit to height data over noted height range (see text for details), after Smith and Jordan [1987]. 63

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en .... c ::;, 0 E ct3 Q) CIJ 101 0 ... Q) .Ll E ::;, z 10 a bin size: 2, range: 200-3302 0 500 1 000 1500 2000 2500 3000 Seamount Height (m) Figure 26. Maximum-likelihood fit to Easter Seamount Chain height data single exponential model. A total of 383 seamounts are observed with heights greater than 200 m. The cumulative number of seamounts are plotted as crosses on the semi-log plot 1be total count in each bin is planed as astrics and a fit is made to these ( not used). Those seamount counts not used in the fit are open circles The solid line is the maximum likelihood fit to the data and cumulative frequency, over the height range of 200-3300 m representing the exponential model, v(H)= Where v(H) is the total expected number of seamounts over a given height (H) in a given area, V0 is the number of seamounts per unit area, W' is the characteristic height of the population [based on Smith and Jordan, 1987]. See Table 3 for results of runs using the same method over different height ranges and bin sizes. (a) Bin size is 50 m W' is 431 m (b) Bins size is 100m, W' is 435 m (Continued on next page) 64

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Figure 26 (Continued) b bin size: 50, range : 200-3300 X 0 500 1 000 1500 2000 2500 3000 Seamount Height (m) (Continued on next page) 65

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Figure 26 (Continued) 103 en c ::s 0 E as Q) 00101 0 .... Q) ..c E ::s z 10 c bin size : 100 range : 200-3300 XXX *<) X 0 1 000 2000 3000 Seamount Height (m) 66

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Figure 27. Single linear least-squares fit to the exponential cumulative frequency size distribution All 383 seamount size data are fit by a single curve, giving equal weight to each data point, these are individual counts i.e. not binned. (a) Height size distribution, fit by an exponential distribution with an r2 c oeffici e nt of .95 p-1 is 574 m (b) volume size distribution, fit by an exponential distribution with an r co e fficient of .64, P"1 is 621 km3

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(3"1 = 574 m = .9 5 N = 383/383) A 1 0 500 1000 1500 2500 3500 Seamount height (m) B (3"1 = 621 = .64, N = 383/383) >. c.> c:: Q) ::J g' ..:: 100 Q) > -..... CIS ::J e ::J c.> 10 co .3 + + + 1 0 2000 3000 5000 Seamount volume (cub. km) 68

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2.6.3 Power-law Distribution The self-similar power law distribution, is described by the equation v(H) =V1H -1 where v(H) is total number of seamounts predicted above height H, V1 is a number of seamounts per unit area, H is the volume or height, and -y is the slope or scaling exponent. The power-law is fit to both height and volume cumulative frequency di s tributions using a linear least-squares regres s ion (Figure 28a and Figure 28b, respectively). This is a two parameter cumulative frequency function [Banon and Scholz, 1995] that describes a self similar distribution of seamount sizes. 2.6.3.1 Height When fitting the height data with a power law using a linear least-squares regression, a change in scaling exponent is necessary at a height of 2450 m. Seamounts with heights less than 2450 m have a scaling exponent of -1.79, while those ab ov e 2450 m have a scaling exponent of -7 29 (Figure 28a) The "roll-off' from the power law at approximately 300 m may be attributed to one or more of the following : a lack of resolution of the GLOLRI-B system; sediment cover; abyssal hill fabric; burial of small seamounts by younger ones; or failure of small seamounts to follow the distribution defined by larger ones. For this reason values below 300 m are not used when applying a line of best-fit (data marked by crosses in Figure 28). The single exponential distribution (Figure 27a) and the multiple power law fit (Figure 29a) describes the height cumulative frequency equally well, with correlation coefficients above 0 94 over the height range of 3300 m to 300 m It is therefore inconclusive which better describes the height distribution of this seamount population, and whether two seamount populations exist based on the distribution of their heights 69

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Figure 28. Multiple linear least-squares fits to the power-law cumulative frequency size di s tribution. A different distribution is fit over different size ranges, to accommodate observed slope changes. (a) Cumulative frequency distribution for height plotted on log log axis. These are power law scaling lines fit with a linear least-squares regression with each having a different fractal exponent ("(). Inflection point at 2450 m Heights less than 300 m are not fit due to a roll-off' (see text) (b) Volume cumulative frequency distribution displayed on a log-log axis There at least two, and possibly three, volume categories with power law scaling lines each with a different scaling exponent. Note inflection at 1200 km3 and 120 km3

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>. u c :s l > ..... :s 100 E 10 :s u 0.0 .3 >. u c :s ar t.!: > ..... ... .$ :s 1 200 100 E 10 :s u 0.0 .3 1 1 A 2450 meters + height<300 o height<2450 'Y = -7.30 (r2 = 0.94 N = 11/383) o height>2450 y= 1.79 = 0.95, N = 295/383) 1000 4000 Log seamount height (m) B + volume<3 A volume<120 "(= -0 88 (r2 = 0.82, N = 295/383) 2 o volume<1200 "(= -1.41 (r = 0.88, N = 60/383) o volume>1200 y= -1.71 (r2 = 0 95, N = 13/383) 10 100 1000 Log seamount volume (km 3 ) 6000 71

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Figure 29 Multiple linear leastsquares fits to the exponential cumulative frequency size distribution Seamount sizes are fit with more than one curve, based on the change of slope observed in the cumulative frequency power-law distribution (a) Cumulative frequency distribution for heights, fit by two curves, with a break at 2450 m. With W' of 553 m, in the high height range, and W' of 393 m for the lower height range. (b) Cumulative frequency distribution for volume. fit by three curves, with a change of slope at 1200 km3 120 km3 and 3 km3 and W' of 150,000 km3 537 km3 and 63 km3 for the volume ranges.

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400 A 2450 meters 0 0 Height> 2450 m (l = 0.95, N = 11/383) Height< 2450 m 393m = 0 95, N = 295/383) 1 0 500 1000 1500 2000 2500 3000 3500 Seamount height (m) 400 B Volume> 1200 150,000 1an3 (r2 = 0.95, N = 13/383) Volume< 1200 537 1an3 (r2 = 0 88, N = 60/383) Volume< 120 63 1an3 ( r2 = 0.82, N = 295/383 1 0 1000 2000 3000 4000 5000 6000 Seamount volume (cub km) 73

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The exponential maximum likelihood fit (Figure 30a) is applied over the same height ranges as those determined by the power-law fit (Figure 28a) The height data is binned at 50 m. The characteristic height of the seamount popu lation 200 2450 m is 379 m, which is not significantly different than the characteristic height over the same height range using the linear least-squares method (Figure 29a) of 393 m Over the height range of 2450-3300 m, = 585 using the maximum likelihood method (Figure 30b) and p-1 = 553 m using the linear least squares regression (Figure 29a). 2.6.3.2 Volume A better fit to the seamount volume cumulative frequency distribution is made with the multiple power law fit (Figure 28b), rather then the single exponential distribution (Figure 27b) The cumulative frequency distribution of seamount volume spans five orders of magnitude (1Q-LIQ4 km3), and is therefor robust for power law analysis. An abrupt change in slope in the power law fit is observed at 1200 km3 to allow a close fit with the linear least-squares estimator to the data (Figure 28b). Seamounts with a volume greater than 1200 km3 follow a power law volume cumulative frequency distribution, with a scaling exponent (y) value of -1.71. Seamounts with volumes between 1200 km3 and 120 km3 have a scaling exponent of -1.41. There may be an additional group with volumes less than 120 km3, with a scaling exponent of -0.88, but it is not clear exactly if a break significantly improves that fit. A roll-off' from the power law fit is obtained with decreasing volume below 3 km3, which we attribute to under-sampling due to lack of resolution (perceptibility limit) and reasons described in section 2.6.3 .1. For this reason values below 3 km3 are not used when applying a line of best-fit. 74

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f/J r::::: ::I 0 103 a bin size: 50, range: 200-2450 E ctl C1> C/) 101 0 .... C1> ..c E ::I z 10 0 500 1000 1500 2000 2500 Seamount Height (m) Figure 30. Multiple maximum-likelihood fit to the exponential cumulative frequency of seamount height distribution. The population is divided into a lower height population between 200-2450 m and an upper height population 2450-3300 m, using 50 m height bins. (a) Maximum-likelihood fit to the lower seamount heights (less than 2450 m), W1 is 377 m, andv0 is 2.6 13. (Continued on the next page) 75

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Figure 30 (Continued) b i n size: 50, range : 2450-3300 b X 0 500 1 000 1500 2000 2500 3000 Seamount Height (m) (b) Maximum likelihood fit to the upper seamount heights (greater than 2450 m), W is 524 m and V0 is 5 48.7 76

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The volume data is then revisiting, and the multiple exponential law fit is applied (Figure 29b) over the same volume ranges as those determined with the power law fit (Figure 28b). The fit to the volume data is not significantly different than that of the power law fit. This suggests that either fit may describe the seamount volume distribution and that perhaps more than one population of seamounts is required to explain their volume distribution. 2.6.4 Discussion It is clear from the shape distribution of seamounts in the study area when viewed in detail, that there is no clear pattern In general, seamounts are coalesced into several broad chains, but in detail they are distributed sporadically, with respect to both size and shape. The seamount population in this region is interpreted as being polygenic This is supported by results from the size distribution analysis, which require that their volume distribution, and possibly their heights as well, be described by at least two different populations, whether fit by an exponential or power law. The implications are that these magmas may have different physical properties; controlled by different viscosity, effusion rate, total magma volume available, and/or the strength/thickness of the lithosphere Information from seamount shape and size distribution, combined with preliminary age and geochemical data [Naar et al., 1993b ; Poreda eta/., 1993a] leads to the proposal that this population is a result of different magma sources, controlled by different physical conditions, presumably plume source volcanism versus ridge processes. 2 6.4.1 Implication of Shape Analysis Values of seamount slope and flatness are scattered ov e r different seamount heights However, their mean value increases with summit height (Figure 12e and Figure 12f) Additionally, the histogram of number versus flatness and slope, appears to be bimodally distributed (Figure 15 and Figure 17 respectively). The break appears to be at a 77

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flatness of about 0.28 and slope of 12. One population is comprised of short seamounts with variable flatness from pointy cones to flattened domes and predominantly steep flanks A second population is of massive, shield-like, pointy seamounts with gentle slopes. The second population is similar to those described by Batiza [1982] as formed by a plume source. These volcanoes may have an unlimited supply of magma, limited only by the strength of the lithosphere upon which they are emplaced Basal radius, cross-sectional area and volume are proportional to summit height, they are fit by a single smooth curve, as seen in 12a, c, d. These results are similar to other studies of Pacific seamounts, derived from crossing profiles using SeaBeam, GLORIA or narrow-beam echo-sounder (Table 4). 2.6.4.2 Implication or the Size Distribution The cumulative frequency height distribution and the cumulative frequency volume distribution, when fit with power law curves, reveal distinct breaks at 2450 m and 1200 km3 respectively (F i gure 28a and Figure 28b). Such a break in the power law fit of cumulative frequency distributions has been attributed to a fundamental change in the physical process of the system [Mandelbrot, 1982]. The spatial distribution of the seamount population, based on height criteria, can be observed in Figure 31. Dark and light gray ellipses represent those seamounts with heights greater than 2450 m, and between 2450 m and 300m, respectively The eleven seamounts (dark gray ellipses) with the greatest height also are those with the greatest volume (Figure 32), (although there is not a one-to-one correspondence in ranking). These seamounts are located along two E-W ridges and a single large seamount to the south, possibly unrelated to the linear ridges [Liu and Naar, 1996a]. Easter Island and a large volcano edifice to the northwest (Moai Seamount) are believed to be products of plume volcanism, based on geochemical studies [Bonatti et al., 1977 ; O Conner et al. 1995]. 78

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Figure 31. Seamount height spatial distribution 383 seamount bases are approximated as regular ellipses Black line represents study area boundary, and thinner black line is the EPR. Legend shows eleven seamounts with heights greater than 2450 m represented as black ellipses, they are picked based on a bend in the power law height cumulative frequency plot (Figure 26a). Seamounts in the height range 2450-300 m are plotted as medium gray and those below 300m as open ellipses.

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----E E 0 8 V"l E _. N 0 "fnl V"l 8 8 N :I:N A 0 e (J .. ' q-,_ 0 ... .:. : .. . e . ., . ... 0 0 ... _.....,. Oo N I 80 0 0 I 0 "' 0 I 0 00 0 I b I 0 N I I

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Figure 32. Seamount volume spatial distribution. 383 seamount bases are approximated as regular ellipses. Black line represents study area boundary, and thinner black line is the East Pacific Rise. Legend shows twelve seamounts with volumes greater than 1200 km3 represented as black ellipses, they are picked based on a bend in the power law volume cumulative frequency plot (Figure 26b). Seamounts in the volume range 1200-3 km3 are plotted as medium gray, and those b elow 3 km3 as open ellipses.

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--- ..., ] Q) ..., 8 E ] N ..2 0 I > 0 ... . 82 ..., ] 8 N 1\ e 0 -.:t 0 I \o 0 I 0 00 0 I I 0 N I

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Preliminary analysis of the Easter seamounts samples by micro-probe of major element geochemistry, shows that silica content increases with volume, which is expected for plume volcanism, possibly due to longer residency time in the magma chamber [Batiza, personal communication, 1995]. Although silica content may not be the most important factor controlling viscosity. Smaller volcanoes may form by non-plume processes, on-or off-axis [Batiza, 1989]. Smith and Jordan [1987] state that in the simplest dynamical model of volcano formation, height is proportional to the hydraulic head owing to the buoyancy of the magma. This assumption, first made by Vogt [1974], implies that (1) volcano size is not limited by the availability of magma so that this equilibrium height is always attained, and (2) the hydraulic head is proportional to the source depth. Thus, an exponential in seamount height distribution could results from an exponential distribution of discrete source depths. The principal conclusion of Vogt's study was that volcano height is primarily limited by the thickness of the lithosphere at the time that the volcano is built, thus larger seamounts are able to be supported by increasing plate thickness. Although this relationship is observed elsewhere, it may not be solely a result of isostatic control. Other factors controlling seamount growth include total magma supply and duration of volcano growth [Wilson et al., 1992]. In many cases, volcanoes may not have reached their maximum height because conduits have opened to flank eruptions or followed other paths of less resistance. The volume power distribution, and possibly the height cumulative frequency power-law fit, show that there are at least two different seamount populations These different populations are proposed to be related to different physical properties of the extruding magma, possibly related to its temperature. The results of characteristic height and seamount abundance are similar to other Pacific studies (see Table 4). However, these "studies do not require two populations to explain their size distribution. Abers et al. [1988] found that both exponential and power law provided equally good fits to their cumulative 83

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frequency-height data. Smith and Jordan [1988] fit their height data with a single exponential curve, using the maximum likelihood fit to a cumulative frequency plot of binned seamount heights However, if fit with two curves (with a similar break at 2200 m instead of our 2450 m) we find the power cumulative frequency curve would have made a better fit A similar treatment is made to this data set, in the height range of 200-3300 m and 50 m bins (Figure 26b). A characteristic height (W1 ) of 431 m, and 2.5.13 seamounts expected per 1000 km2 is obtained using this method. A total of 381 seamounts with heights greater than 200 m are predicted to occur in the study area (243,000 km2), not significantly different than the 382 seamounts counted (see Table 3). Varying the bin size does not effect the two independent parameters significantly, they are both within their error ellipse (see upper portion of Table 3). However varying the height range by allowing for increasing bin sizes, does effect the characteristic height parameter significantly (see lower portion of Table 3). The characteristic height over the height range of 200-1050 (eliminating bins of 0 counts from the fit) is 303 m. The seamount density (v 0 ) is 2.7 per 1000 km3 Again the predicted number of seamounts of 348, is not significantly different than the 323 seamounts counted These value are comparable with other studies in the southern EPR, also at fast spreading rates. Kleinrock and Brooks [1989] suggests that in medium to slow spreading rates, on-axis volcanoes increase in size and decrease in abundance. However, it seems that when comparing fast and slow spreading rates the opposite is true. Seamounts increase in size and decrease in abundance with increasing spreading rate. The results from this study appear to fit this trend (see Figure 33). The relationship between the V0 and spreading rate is not as clear, however it seems to follow an inverse relationship. 84

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Table 4. Comparison of seamount size distribution parameters with other studies Study Region H e ight v o p-1 mean f mean [latitude] range (m ) (1103 krn2 ) (m) [range] [range] This study ESC 200-1050 2.7 .15 303 0.15. 1 1o.0 [27-29S] 200-3300 2 .5. 13 433 [0. 57] [2-27] Scheirer et al. S EPR 2001200 4 .8.3 4 2 1 0 .05.14a 13 38 (1996) [15-19S] [0. 76] [5-35] Scheirer & N .EPR 2 0 0-800 1.9 2 240 Macdonald [8-18N] [0-0. 6] [5-25] (1995) Abers et al. S. P a cific 100-1000 1 2.6.8 174 (1988)b [7 22S] Abers et al S. Pacific 100-600 27.18.6 6 8 (1988)c Bemis & Smith S. Pacific 300-700 13 233 0 .16. 19 (1993)d [9-22S] [0-.8] Smith & Jordan Eastern 400-2500 5.4.7 285 0 3 1 18 18 (1987), Smith Pacific e [0. 69] [5 36] (1988) Kle inrock et al. Galapagos 50350 37o 29 0 .3. 1 13 (1994) [2N] 95W [0. 6] [6-32] Smith&Cann MAR 50-210 195 5 8 0.31.16 15 (1990; 1992) [24-30N] [0. 7] [5-28] Magde & Smith N.MAR 50250 31o 68 0.46. 2 23 (1995) [57-62N] [0-.9] p-1 is the characteristi c height; v o is the total expected number ; f i s the flatness ; is the slope; ESC is the Easter Seamount Chain; EPR is the East Pacific Rise ; MAR is th e Mid Atlantic Ridge Calculated from published data b Whole reg i on, 0 40 Ma; c EPR region, 0 2 Ma d Wide b e am data from EPR region e All regions 85

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400 ,.-------------500 -0 -C N 300 ] & 200 .... E :I c ] 100 8. r2 = .88 R 0 10 20 30 40 50 60 Half spreading rate (mm yr I) 70 80 Figure 33. Seamount shape parameters versus spreading rate. A linear least-squares fit is made to the characteristic height data, using 7 points. Six data points are from other studies and shown in Table 4, the data point from this study has the fastest spreading rate. The characteristic height
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2.6.4.3 Geochemical Predictions Based on the sharp break in the power law fit to the size cumulative frequency distributions (Figure 28), we propose that at least two different physical processes control seamount production in the study area, possibly related to a viscosity difference. If this viscosity difference is related to distinct temperature or tectonic regimes, certain geochemical signals may be expected. Plume-fed seamounts are formed from a larger, deeper hotter and more enriched source, so their geochemistry is predicted to show: (a) a distinct geochemical signal, although highly variable, owing to a heterogeneous source; (b) a more primitive than N-MORB chemistry, with high Mg# (66-68), similar to other ocean island basalts (OIB) [Bariz.a et al., 1989]; (c) an enriched LREE chemistry, unless the magma re-equilibrated with depleted mantle during ascent [Shen et al., 1993]; (d) evidence of formation from a less viscous lava and hotter source, such as sheet flows and low slope; and (e) higher Si02 due to the longer residency time in the magma chamber. It is unclear what the signal would be from a plume source, because viscosity depends on both temperature and silica content The factors which influence magma viscosity include high dependence on temperature, effusion rate and chemistry. Observing that the larger seamounts have low slopes and yet higher silica content [Batiza, 1996, personal p communication], suggests that temperature and/or effusion rate may be more important in controlling viscosity, rather than silica content. The more numerous but smaller seamount population, presumably formed by non plume material, are expected to show: (a) evidence of having formed from a more viscous lava source, possibly extruded as rubble flows; (b) a composition closer to that of N MORB; and (c) lower Si02 content, due to shorter time allowing for partial differentiation. Observing that the smaller seamounts have higher slopes and flattened morphologies, although possibly due to the lack of magma supply and hydrostatic pressure preventing 87

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fragmentation of the flow [Binard et al 1992], suggests that they may have formed from a more viscous and thus cooler magma source, as predicted Age difference between the seafloor and the seamount does not appear to be an important parameter in the factors which control seamount production A plume source may be near-axis or off-axis, and still produce the characteristic shape The flatness and slope versus height plots (Figure 12e and Figure 12f) do not have a break at 2450 m, one can possibly be seen at about 1200 m instead. Although not well constrained, this may indicate that a third population exists, having heights between 1200 m and 2450 m. A possible origin for this population is an off-axis non-plume origin, such as fracture zones, or mixing between the end members These may have been formed by a similar physical process as the many small seamounts and consequently, not resolved in the cumulative frequency power-law model. Their chemistry is predicted to be a mixture of plume and ridge signal, and having a variable age off-set from the underlying seafloor These specific observations can be used to help determine whether the different physical processes indicated for the subpopulations can be explained as non-plume versus plume volcanism, and also eliminate or support the various models proposed for the formation of ESC (described in Chapter One) 2.6.4.4 Implications of the Results to the Proposed Models for the Formation of the Easter Seamount Chain As proposed above the formation of the Easter seamount population is from more that one process. Young seamounts are found close to the ridge axis as well far off-axis. It is observed from side-scan intensity and preliminary radiogenic age data, that volcanism is not contemporaneous along the entire length of the chain. Large seamount edifices (>2450 m and 1200 km3 ) are only found on seafloor age greater than Chron 3 (-4 Ma) (Figure 30 and 31), or a distance greater than -300 km from the axis, assuming a half spreading rate of 75 km/m.y [Demets, 1994] Additionally the ages of the large 88

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seamounts are much greater than the age of the seafloor up on which they lie, with ages ranging from 0.08 Ma to 2.6 Ma on top of -8. 5 Ma crust (Figure 34 compared with Figure 3) [Liu 1996; R. Duncan, personal communication 1996; O'Connor et al., 1995] These ages are based on 40 Ar/39 Ar age measured on plagioclase (only those ages from GLOR07MV cruise, and previously published are reported here) [R. Duncan, personal communication, 1996; Liu, 1996; Naar et al., 1993a]. Ages seem to increase from east to west along at least two dominant sub-parallel tracks, with trends 10-15 clockwise relative to absolute plate motion (Nazca-Hotspot motion calculated based on trends of three major chains on the Nazca plate) [Liu, 1996] Geochemical studies show an enriched plume signal influence in samples along the East Rift of the Easter microplate, with the strongest signal at -27S [e.g. Schilling et al., 1991]. Samples along the ESC show a pure plume pure MORB or a mixture of the two side by side along the ESC [Haase and Devey, 1996; Haase et aL, 1995]. As well, analysis of the effective elastic thickness (Te), which gives an indication of the relative time of seamount loading, has been determined to be uniform along the ESC and generally being low (fe -3 km) [Liu 1996]. This suggests that the source of the volcanism has been relatively near the ridge axis for the past 9 Ma. The different proposed models for the formation of the ESC may be assessed from the findings of this study, and oth e r information described above Based on the location of the largest seamounts and their relative age to the underlying seafloor it may be ruled out that the largest seamounts have formed on the ridge-axis and then carried off. Their location and age is consistent with a process occurring off-axis. The ESC study area is observed to have the following: (1) a uniform e lastic thickness; (2 ) a gross age progression to the east, possibly along at least two sub-parallel tracks; and (3) an occurrence of at least 89

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Figure 34. Age data collected from GLOR07MV cruise. Stars and associated ages (minimum age of samples in millions of years before present) are based preliminary results from dredge samples collected along the ESC. Filled diamonds are those samples whose age is age of samples in millions of years before present) are based preliminary results from dredge samples collected along the ESC. Filled diamonds are those samples whose age is not available (N/A) at this time [R. Duncan personal communication, 1996; Liu, 1996]. Several gross subparallel trends are seen from west to east. Much of the volcanism is much younger than that of the seafloor (based on magnetic isochrons, figure 3), with delta ages from -2-9 Ma

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--0 10 N I 0 o 0 0 0 0 ()<:;) oo oo 91 0 0 00 N I 0 -.::t 0 I 0 10 0 I 0 00 0 I 0 0 I I

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two seamount populations, based on their size distribution These observations cannot be accommodated by the models which predict simultaneous volcanism along the length of the chain, such as the "leaky fracture zone" [Clark and Dymond, 1977], "diffuse extension" [e. g. Sandwell et al., 1995], and "hot line" [Bonatti and Harrison, 1976]. The diffuse extension model (Figure 5c) predicts N-S stress and thinning of the lithosphere, creating troughs along which minor upwelling would occur and seamount formation would be favored There is no evidence of such topographic lows nor ridge-parallel fissures. Secondary convection rolls or "hot lines" (Figure 5d) predict volcanism to form along topographic highs the occurrence of which is not observed in the detailed bathymetry The geochemical and shape distribution results better support a model which predicts interaction between an off-axis plume and material feeding the ridge axis (Figure 5a) [e.g. Fontignie and Schilling, 1991 ; Haase et al., 1996; O'Conner et al., 1995; Schilling et al. 1985a]. The popu l ation consists of at least two types of seamounts which have formed from magma having different physical properties A temperature control is proposed here to explain the differences in inferred viscosity, based primarily on flatness and slope distributions. A hot source is predicted to produce lower viscosity flows, and form pointy seamounts with gentle slopes. The geochemical signal of the seamounts would be expected to be that of ocean island basalt (OIB), a pure plume signal, if their magma source is decoupled from that of the ridge axis. However results of geochemical studies describe a mixing between the end members [e.g. Hanan and Schilling, 1989; Poreda et al., 1993b; Haase and Devey, 1996]. This study does not have sufficient resolution to determine whether the flow of material is from the ridge to the plume [Haase et al., 1996], from the plume to the ridge [e.g. Schilling, 1991], or both. Results of shape distribution suggest that mixing among different sources i s occurring over a regional scale. As well, the spatial distribution of seamount shapes ind i cate that a simple rising plume is not responsible for the extensive volcanism. Rather, it seems that material is rising 92

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simultaneously at several locations, and this material has different physical properties, leading to differences in viscosity. Perhaps mixing of different material is occurring at shallow depth, thus lavas showing plume signature erupts close to other having a mixed source, as well as superposition over seamounts formed exclusively at the ridge axis [Haase et al. 1996]. The hybrid hot spot model of rising and shearing of mini-plumes [Ihinger, 1995; Liu, 1996], seems to explain the age data, but lacks a satisfactory explanation for the formation of at least two distinct populations, and mixing of MORB and om material. 2 7 Conclusions Based on the distribution of seamount shapes (slope and flatness), at least two seamount populations are identified in the study area: (1) Small volume volcanic edifices with variable flatness from small pointy cones to flattened-domes and steep slopes; and (2) massive volcanic edifices with pointy summits and low slopes. Th e seamounts cover -27% of the seafloor and make up 4.3% of the total crustal volume. The few large seamounts contribute to the majority of the volcanic volume in the area. Over 50% of the total volume of seamounts used in this study is made up by the 14 largest seamounts and the remaining volume by the 369 smaller seamounts. The cumulative frequency distributions of height and volume suggest that at least two populations of seamounts are present, based on a distinct break at approximately the same point in the seamount size distributions. Whether the power law fit or the exponential fit is used, at least two distinct sub-populations are required For both volume and height, these distinct subsets are proposed to be related to different underlying physical processes (following Mandelbrot [1982]) which result in different styles of volcanism. The different physical processes presumably result in observable differences in geochemistry and morphology between non-plume and plume volcanoes. Geochemical data being analyzed 93

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[Poreda et al. 1993b; R. Duncan personal communication, 1996] will allow testing of the range of viscosity from which these seamounts fanned, giving an indication of the temperature of the source. These results may possibly help explain the classes of seamounts observed. Observations made in this study along with other age and geochemical results, place constraints on the preferred model used to explain the fonnation of the ESC Lithospheric stretching, secondary convection, and leaky fracture zone models may be ruled out, because they predict contemporaneous ages along the entire length of the ridge, and this not seen in age data The Lithospheric stretching and secondary convection models predict linear seamount ridges perpendicular to the ridge. The occurrence of this lineation is not supported by the bathymetry data Instead wide spreading volcanism is observed, with at least two major and sub-parallel ridges. The source of the volcanism is proposed to be polygenic by this study, instead of being derived exclusively from a warm, deep mantle source as predicted by the lithospheric stretching, secondary convection, and leaky fracture zone models The simple hotspot model [Morgan, 1972; Pilger and Handschumacher, 1981] does not satisfactorily explain the non-linear age progression from west to east, and the different types of seamounts juxtaposed one beside the other. The observations are better explained by a combination of the hotspot-ridge channeling model [Haase et al., 1996; Schilling, 1995] and the sheared hotspot model [lhinger, 1995; Liu, 1996]. Finding chemically diverse samples side by side, and seamounts having different shape properties side by side, is compatible with a model predicting a mixing between om (being warm and having low viscosity) and MORB (being cooler and more viscous) material Our findings support a mixing model of material at the ridge or further from it, although the majority of plume type volcanism has been relatively near the axis for the past 9 Ma. The threedimensional nature of plumes may result in the outflow of material in several locations at the same time 94

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It is evident that more studies are required to resolve the relationship among seamount's source temperature, chemistry, effusion rate and their effect on seamount shape The distribution of seamount sizes is a valuable analytical tool. It however, requires an extensive data set. Identification of smaller seam o unts by higher resolution studies is needed to test the distribution model at the lower end ( les s than 200 m ) 95

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REFERENCES Abers, G.A B. Parsons, and J.K. Weisse!, Seamount abundances and distributions in the southeast Pacific Earth and Planetary Science Letters, 87, 137-151, 1988. Alexander, R.T., and K.C Macdonald, Small off-axis volcanoes on the East Pacific Rise, Earth and Planetary Science Letters, 139, 387-394, 1996. Allan, J.F., R. Batiza, and P. Lonsdale, Petrology and chemistry of lavas from seamounts flanking the East Pacific Rise axis, 21 N : Implications concerning the mantle source composition for both seamount and adjacent EPR, in Seamounts, Islands, and Atolls, edited by B .H. Keating, F. Patricia, R. Batiza, and G.W Boehlert, pp 255-282, AGU, Washington, D. C., 1989 Barton, C.C., and C.H. Scholz, The fractal resource assessment and exploration strategy, in Fractals in Petroleum Geology and Earth Processes edited by C .C. Barton, and P.R La Pointe, Plenum Press, New York, 1995. Batiza, R., Abundances, distribution and sizes of volcanoes in the Pacific Ocean and implications for the origin of non-hotspot volcanoes, Earth and Planetary Science Letters, 60, 195-206, 1982. Batiza, R., Seamounts and seamount chains of the eastern Pacific, in The Geology of North America, edited by E .L. Winterer, D.M. Hussong, and R.W Decker, pp. 289-306, Geological Society of America, Boulder, Colorado, 1989. Batiza, R., P J. Fox, P.R. Vogt, S.C. Cande, N R. Grindlay, W.G. Melson, and T O Hearn, Morphology, abundance, and chemistry of near-ridge seamounts in the vicinity of the Mid-Atlantic Ridge -26S, Journal of Geology, 97,209-220, 1989. Batiza, R., and D. Yanko, Petrology of young Pacific seamounts, Journal of Geophysical Research, 89 (B 13), 11235-11260 1984. Bemis, K.G and D.K. Smith, Production of small volcanoes in the Superswell region of the South Pacific, Earth and Planetary Science Letters, 118, 251-262, 1993. Binard, N., R Hekinian, R.C. Searle, and P. Stoffers, Morphological and structural studies of the Society and Austral hotspots in the South Pacific, Tectonophysics, 186, 293-342, 1991. Bird, R T and D.F. Naar, Intratransform origins of mid-ocean ridge microplates, Geology, 22, 987-990, 1994. 96

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Bonatti, E., and C.G.A. Harrison, Hot Lines in the Earth's Mantle, Nature, 263, 402-404, 1976. Bonatti, E., and C.G.A. Harrison, Eruptive styles of basalts in oceanic spreading ridges and seamounts: Effect of magma temperature and viscosity, Journal of Geophysical Research, 93 (B4), 2967-2980 1988. Bonatti, E C G A. Harrison, D E. Fisher, J Honnorez, J.G. Schilling, J .J. Stipp, and M. Zentilli, Easter volcanic chain (Southeast Pacific): A mantle hot line, Journal of Geophysical Research, 82 2457-2478, 1977 Cande, S.C and D.V Kent, Revised calibration of the geomagnetic polarity timescale for the Late Cretaceous and Cenozoic, Journal of Geophysical Research, 100 (B4), 6093-6095, 1995. Chen, Y., and J. Morgan, Journal of Geophysical Research, 95 17583-17604, 1990. Chen, Y.J., Oceanic crustal thickness versus spreading rate, Geophysical Research Letters, 19 (8), 753-756, 1992. Clark, J.G and J Dymond, Geochronology and petrochemistry of Easter and Salay Gomez Islands : Implications for the origin of the Sala y Gomez Ridge, Journal of Volcanology and Geothermal Research Research, 2, 29-48 1977. Danobeitia, J.J., J.P. Canales, N. Vidal, J. Gallart R.I. Carbonell, J. Diaz, M. Farran, D F. Naar, J. Francheteau, A.P. Slootweg, and G A Dehghani, Geophysical study along the Easter-Salas y Gomez volcanic ridge (Southeast Pacific), InterRidge News, 4 (1), 19-22, 1995. Davis, E E., and J .L. Karsten, On the cause of asymetric distribution of seamounts about the Juan de Fuca ridge : ridge-crest migration over a heterogeneous asthenosphere, Earth and Planetary Science Letters, 79, 385-296, 1986. DeMets, C ., R. Gordon, D.F. Argus, and S. Stein, Effects of recent revisions to the geomagnetic reversal time sca l e on estimates of current plate motions, Geophysical Research Letters, 21 (20), 2191-2194, 1994. DeMets, C. R.G. Gordon D F. Argus, and S. Stein, Current plate motions, Geophysical Journal International, 101 425-478, 1990 Duncan, R.A., and M.A. Richards, Hotspots, mantl e plumes, flood basalts, and true polar wander, Review of Geophysics 29 (1), 31-50, 1991. Epp, D., Possible perturbations to hotspot traces and implications for the origin and structure of the Line Islands, Journal of Geophysical Research, 89 (B13) 11273-11286 1984 Fontignie, D., and J.-G Schilling, Sr and REE a!o':lg the Easter boundaries (South Pacific): Application of muluvanate statistical analyses to ndge segmentation, Chemical Geology, 209-241, 199L 97

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Herron, E.M., Sea-floor spreading and the Cenozoic history of the East-Central Pacific, Geological Society of America Bulletin, 83, 1672-1692, 1972a. Herron, E M., Two small crustal plates in the S o uth Pacific near Easter Island, Nature, 240, 35-37' 1972b Hey, R N ., P.D. Johnson F. Martinez, J. Korenaga M .L. Somers, Q J Huggett, T P LeBas, R I. Rushy, and D F. Naar Plate boundary reorganization at a large-offset rapidly propagating rift, Nature, 378, 167-170, 1995 Hey, R.N., D F. Naar, M.C. Kleinrock, W.J P. Morgan, E. Morales, and J.-G. Schilling Microplate tectonics along a superfast seafloor spreading system near Easter Island, Nature, 317 (6035), 320-325, 1985. Holocomb, R T and R C Searle Large landslides from oceani c volcnoes Marine Geotechnology, 10, 19-32, 1991. Ihinger, P.D., Mantle flow beneath the Pacific Plate : Evidence from seamount segments in the Hawaiian-Emperor Chain, American Journal of Science, 295 (N o vember), 1035-1057, 1995. Jackson, E D and H R Shaw, Stress field in central portions of the Pacific Plate : Delineated in time by linear volcanic chains, Journal of Geophysical Research 80 (14), 1861-1875, 1975. Jordan, T.H W. Menard, and D.K Smith, Density and size distribution of seamounts in the Eastern Pacific inferred from wide-beam sounding data, Journal of Geophysical Research, 88 (B12), 10508-10518, 1983. Karsten, J L and J R Delaney, Hot spot-ridg e crest convergence in the Northeast Pacific, Journal of Geophysical R es earch, 94 (B1), 700-712 1989. Kincaid, C., J.-G. Schilling, and C. Gable, The dynamics of off-axis plume-ridge ineraction in the uppermost mantle, Earth and Planetary Science Letters, 137, 29-43, 1996 Kleinrock, M.C., and B .A. Brooks, Construction and destruction of volcanic knobs at the Cocos-Nazca spreading system near 95W, Geophysical Research Letters, 21 (21), 23072310, 1994. Larson, R L., R C. Searle, M.C Kleinrock H Schouten R T Bird, D.P. Naar, R.I. Rushy, E.E. Hooft, and H La s thiotakis, Roller-bearing tectonic evolution of the Juan Fernandez Microplat e Nature, 356,571-576 1992. Liu, Z., and D.F. Naar, Side-scan processing of GLORIA-B and S e aBeam 2000, Marine Geophysical Researche s 1996a Liu, Z., and D.F. Naar, Swath bathymetry processing of GLORI-B and SeaBeam 2000, Marine Geophysical Research e s, 1996b. Liu, Z.J., The Origin and Evolution of the Easter Seamount Chain, Ph.D. thesis, University of South Florida, Saint Petersburg, 1996. 99

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APPENDICES 105

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Figure 35. Index to all 383 seamounts u se d in this s tudy. Regions (A thru E) with some overlap, represent boundaries of the following five figures. Shaded regions are approximate basal outlines of seamounts, and their seamount identification number is printed at their apex (see table in Appendix 2)

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> t-r:l z t:;j 1-4 ..... 1-4 z t:;j t-r:l 1-3 0 en t-r:l > 0 Cj z 1-3 en Cj en t-r:l t:;j 1-4 z 1-3 ::c en en 1-3 Cj t:;j

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APPENDIX 1 (Continued) -26 A -27 -28 -29 -113 <529 <531 t!i61 GW5 t n 826 3 6429 tm 1659 -112 t'!58 fw1 -111 '478 "'66 -110 Figure 36. Detailed index to seamounts used in this study. Regions are outlined in the previous figure and seen in more detail in the next five sections of this figure (A thru E) (Continued on next page) 108

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APPENDIX 1 (Continued ) F ig ure 36 ( C o ntinu e d ) a; a-"" ';' "" .tO!i Jr-.. "'"f;t! r-"' II:"' i "' e "" i N M "' c t:' ;z NC' a"' r:' "' 'o:t t'or. 'o:t C': 00 ('I I 'o:t a-:;' "" "' C" r-"' "' "' t" a-"' ..... c "" N c "" 109 .... !'P "' -' ..... ..... Q B 0\ ('I I I I I -I ( C o ntin ued o n n ext page)

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APPENDIX 1 (Continued) Figure 36 (Continued) -28 <:244 952 c -29 -Ios -107 -106 (Continued on next page) 110

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APPENDIX 1 -(Continued) Figure 36 (Continued) 0 D 0 If") N I 111 0 rN I I r-0 I 0 00 0 I 0 0\ 0 I (Continued on next page)

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APPENDIX 1 (Continued) Figure 36 (Continued) -25 tw -26 078.9 -27 E f!07 -28 -106 -105 -104 112

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APPENDIX 2. SHAPE STATISTICS FOR SEAMOUNTS WITH HEIGHTS GREATER THAN 200 METERS Reference Longitude, Latitude, Height Height, Volume, Basal Cross-Flatness "E "N Ranking m km) Area, km1 sectional (Summit: Area, Basal k.ml Axis) 287 -105' -26 28' 1 3300 3278 2139 100 o O 1 106 1 09 22' -27 5' 2 3280 5340 3757 132 o 23 383 -106 25 -27 8' 3 2990 3288 2489 111 o08 274 -106 31' -26 21 4 2940 3077 2241 95 o04 326 -103 51 -26 6' 5 2840 1754 1685 80 o 01 286 -105 33' 26 25' 6 2740 2381 1 63 2 86 o03 279 -106 o -26 25 7 2740 1938 1343 59 0 01 311 -104' -26 24 8 2600 1057 892 52 004 283 -106 11' -26 40' 9 2590 1324 911 68 004 312 -104 58' -26 39' 10 2510 19 9 1 1485 76 002 105 109 41 27 6' 11 2480 643 649 42 005 280 -106 5S -26 52' 12 2410 398 525 42 002 379 -106 23' -27 40' 13 2250 900 815 49 o 01 418 -105 o -27 15 14 2090 1951 1745 58 o06 410 105 20' -27 34' 15 2020 961 701 33 006 252 -107 25' -27 59' 16 1930 190 236 21 006 384 -106 4' -27 1' 17 1930 581 608 37 002 79 -107 14 26 35' 18 1900 374 671 43 o07 501 -110 36' -27 41' 19 1800 972 1019 38 0 13 393 -105 55' -27 47' 20 1790 408 310 23 0 17 175 -108 28' -27 16 21 1720 283 336 19 0 13 544 -110 14' 26 59' 22 1710 1616 1689 55 o O 1 285 -105 35' 26 53' 23 1630 843 840 35 0 01 407 -105 43' 27 41' 24 1610 405 319 21 010 325 -104 20 -26 1 0 25 1600 230 322 18 o02 80 -107 24' -26 27 26 1590 38 101 31 009 111 -108 49' 27 17 27 1500 304 344 20 o08 284 -105 54' -26 43 28 1480 84 9 680 26 002 88 -107 33' -26 19 29 1470 226 332 21 004 77 107 31' -26 53' 30 1420 89 197 26 003 498 -110 34' 27 53' 31 1410 264 346 17 o02 417 105 18 26 59' 32 1410 477 523 21 006 336 -104 34' -25 40' 33 1390 422 653 29 003 564 108 1' 26 24' 34 1350 78 371 19 o13 562 -107 59 -26 16 35 1350 145 412 17 o02 380 -106 21' -27 25' 36 1350 447 48 5 22 o03 17 109 9 -26 41' 37 1350 272 563 19 o02 451 111 9' 28 26 38 1340 407 538 19 o08 186 -108 8' -27 28' 39 1340 638 602 21 o03 349 104 17' 26 24' 40 1320 968 1074 27 002 228 107 53' 27 33' 41 1320 665 578 27 o03 499 -110 14. -27 49' 42 1300 809 1042 29 002 281 -107 1 -26 58' 4 3 1260 45 88 10 0 11 282 106 26 -26 37' 44 1230 463 490 20 o07 89 107 37' -26 11' 45 1230 54 100 9 003 405 -105 40 27 29' 46 1220 230 223 13 o04 495 -110 44' 28 14' 47 1220 493 777 29 o O 1 143 109 9' -27 59' 48 1210 440 527 25 0 11 323 -103 55 26 27' 49 1210 262 376 15 o03 335 -104 21 25 52' 50 1110 344 508 19 004 238 107 26' -27 30' 51 1110 352 336 15 o14 113

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APPENDIX 2 (Continued) Reference Longitude, Latitude, Heigbt H e igbt, V o lume, Bas al Cros sFlatness "E "N Ranking m km) Area, km2 sectional (Summit: Area, Basal kml Axis) 196 -107 55' 28 6 52 1110 232 423 14 .05 515 -112 7' 2 6 49' 53 1100 50 80 7 .12 529 -111 9' 26 43' 54 1080 9 11 3 .09 30 -108' 26 18 55 1080 296 561 18 .02 104 -109 55' 27 2 56 10 3 0 233 414 11 .43 220 -107 58' 27 39' 57 1020 71 72 6 16 543 -110 30' -27 6' 58 1010 249 301 12 .02 237 -107 34' -27 26' 59 1000 147 152 8 12 453 111 10' -28 40' 60 1000 503 788 17 .05 83 -107 11. 26 1 61 980 9 27 1 3 .03 219 -108 1' -27 45' 62 970 65 114 8 .06 239 -107 24' -27 15' 63 960 157 210 9 .06 424 112 46' -27 41 64 920 238 301 13 .08 245 107 4 -27 33' 65 920 234 299 11 11 98 107 54' -25 55' 66 920 37 83 6 .20 314 -104 33' -26 45' 67 910 554 657 13 .03 411 -105 12 -27 3 6 68 870 57 48 5 13 76 107 42' -26 56 69 870 551 655 13 17 486 110 6' -28 4' 70 870 103 163 7 .15 182 -108 7' -27 17' 71 860 23 33 4 .16 341 -103 55 -25 38' 72 850 92 166 6 .24 67 -108 14 -26 39' 73 850 12 27 10 .08 276 -106 4 -26 7 74 840 272 429 10 .03 346 106 32' -26 49' 75 840 48 58 4 .05 212 -107 27' -28 11' 76 830 132 179 7 .05 339 104 5' -25 38 77 810 118 195 10 .02 125 -109 50' -27 59 78 810 156 230 8 .06 443 -111 43' -27 27' 79 810 89 145 8 .03 217 -107 37' -27 51 80 800 47 60 4 .11 251 107 31' 27 54' 81 780 56 101 6 12 246 -107 8' -27 38' 82 760 66 79 5 17 428 -112 47' 27 53' 83 760 85 103 6 .12 268 -106 52' -26 14' 84 760 101 192 7 .04 248 107 8' 27 52' 85 750 146 277 8 .10 275 -106 15' -26 12' 86 740 115 190 6 .08 488 110 7' 27 59' 87 710 33 45 3 .06 401 105 39' 27 2 88 710 75 118 6 .09 492 110 24' 28 1 o 89 700 79 125 5 .05 247 107 17' -27 41 90 700 146 177 8 .07 450 -111 16 28 18 91 700 56 156 5 15 504 110 29' -27 19 92 690 108 127 6 .37 372 -106 20' 27 53' 93 690 96 83 4 .04 548 -ll0 30' -26 48' 94 690 68 89 5 .05 415 105 27' 27 19 95 680 383 360 7 13 256 -107 3. -27 54' 96 680 138 326 8 13 75 -107 36' -26 46' 97 670 305 491 7 .09 552 -ll0 19' 26 29' 98 660 70 105 4 .08 121 -109 48' 27 53' 99 650 47 81 4 .10 310 -104 51' 26 14' 100 640 28 45 3 .12 78 107 10' 26 48' 101 640 1215 1473 5 .12 549 110 33' -26 53' 102 640 53 97 5 .06 93 107 49' -26 8' 103 630 24 99 4 .04 114

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APPENDIX 2 (Continued) Reference Longitude, Latitude, Height Height, Volume Basal CrossFlatness "E "N Ranking m km' Area,lcm1 sectional (Summit: Area, Basal kml Axis) 412 -105 2 -27 30' 104 630 9 25 2 .08 61 -108 4' -26 55' 105 630 40 72 4 .08 183 -108 10' -27 3' 106 630 9 15 2 18 563 -108 25' -26 13' 107 630 19 148 6 11 62 -107 55' -26 52' 108 620 51 130 4 .05 102 -108 4' -25 1 109 620 9 112 5 .02 204 -107 42' -28 25' 110 610 21 44 3 .04 491 -110 20' -28 4' 11 1 610 39 69 3 .22 547 -110 23' -26 43' 112 610 11 16 2 .04 318 -104 17' 26 47' 113 600 57 81 4 .09 490 -11o 15 -28 5' 114 600 34 65 4 16 222 -108 2' -27 33' 115 590 1 1 19 2 .08 556 -110 32' -26 34' 116 590 28 75 4 15 291 106 0 -25 42' 117 590 6 14 1 16 480 -uo 7 -28 30' 118 590 19 35 2 .26 540 -110 48' -26 55' 119 590 54 63 4 15 227 -107 41 27 32' 120 590 47 65 6 .11 265 -106 57' -25 58' 121 580 17 58 3 .28 542 -11o 36' 27 1 0 122 580 44 68 3 15 116 -109 38' -27 27' 123 580 101 127 5 .11 84 -107 23' -26 9' 124 580 4 13 2 17 206 -107 36' -28 19' 125 580 13 29 2 .09 195 108 9 28 1 126 570 99 208 6 .09 322 -103 47' -26 27 127 570 93 147 4 .04 69 -107 52' -26 27' 128 570 2 6 2 .10 489 -11o 10' -28 3' 129 560 13 23 2 .08 197 -107 50' -28 2' 130 560 32 70 4 .08 173 -108 35' -27 34' 131 560 135 186 4 .08 47 108 26' -26 6 132 550 26 75 4 .07 398 -105 52' -27 3' 133 550 79 93 7 .08 342 -104 40' 25 43' 134 540 6 18 2 .04 43 -108 46' -26 19' 135 530 5 20 2 .55 226 107 31' -27 46' 136 530 194 199 5 .08 255 -107 4' -28 6 137 530 74 192 5 .03 214 -107' -2 8 3 138 530 5 12 2 .10 404 -105 48' 27 28' 139 520 41 52 3 .24 59 108 13' -26 50' 140 520 25 53 2 .07 373 -106 18' -27 57' 141 510 46 47 3 .04 211 -107 23' -28 13' 142 510 5 14 2 11 487 -110 4' 28 0 143 510 10 17 2 13 361 -106 38' 27 43' 144 510 51 114 4 .10 360 106 42' -27 40' 145 510 48 87 3 .06 382 -106 35' -27 27' 146 510 22 32 2 12 558 -111 46' 27 44' 147 510 39 15 4 .04 184 108 6' 27 3' 148 510 38 61 3 .03 96 -107 55' -26 2 149 510 6 16 2 .06 493 -110 30' -28 12' 150 510 17 37 2 13 359 -106 49' -27 36' 151 510 83 145 4 18 27 -108 42' -26 42' 152 510 17 42 2 .08 50 108 9' -25 59' 153 510 1 1 32 2 01 550 -110 35' -26 48' 154 500 61 88 4 .05 188 -108 21' -27 33' 155 500 13 18 1 .20 115

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APPENDIX 2 (Continued) Reference Longitude Latitude, Height Height, Volume, Basal Cross-Flatness "E "N Ranking m km) Area, km 1 sectional (Summit: Area Basal kml Axis) 213 107 37' -28 2' 156 500 22 61 3 .08 400 -105 44' -27 8' 157 500 37 65 3 .05 55 -108 26' -26 37' 158 490 13 33 2 .30 81 -107 11' -26 24' 159 490 7 25 4 .04 194 -108 21 -28 4' 160 490 9 25 2 .22 90 -1 07 39' -26 9' 161 490 3 11 1 .22 60 -108 9' -26 58' 162 490 39 64 3 11 209 -107 19' -28 17' 163 490 4 14 1 21 72 -107 43' -26 25' 164 490 83 158 1 .29 496 -uoo 54' -28 5' 165 480 11 28 2 .30 535 -111' -27 1 0 166 480 146 178 4 .23 200 108 15' -28 25' 167 480 6 16 1 .17 135 -109 39' -28 25' 168 470 35 77 3 .08 378 -106 14' -27 37' 169 470 38 64 2 .06 97 -108 3' -26 3' 170 470 5 18 1 05 56 -108 29' -26 43' 1 71 470 9 30 2 .22 288 -to5 37' -26 9' 172 470 4 11 1 19 343 -104 35' -25 48' 173 460 38 65 3 .09 64 -107 52' -26 47' 174 460 34 83 3 .22 351 -106 43' -27 8' 175 460 32 72 3 .04 497 -111 2' -28 6' 176 460 1 1 28 2 .13 250 -107 22' -27 52' 177 460 14 26 1 .20 66 -tos 3' -26 34' 178 450 191 341 3 13 319 -104 15' -26 44' 179 450 30 51 3 .08 244 -107 10' -27 17' 180 450 8 13 I 17 513 -112 24' -27 13 181 450 48 81 3 .20 131 -109 43' -28 17' 182 450 19 47 2 .12 481 -uo 7' -28 25' 183 440 11 27 2 12 516 -n1 59' -27 1' 184 440 68 108 3 .10 560 -no 43' -26 50' 185 440 86 141 3 .07 261 107 14' -26 14' 186 440 8 28 2 13 82 -107 11' -26 16' 187 440 238 495 2 .29 243 -1 07 3' 27 13' 188 440 45 86 3 .09 506 -no 51' -27 21' I89 440 92 195 4 .03 99 -1os I' -25 55 190 440 20 86 3 .09 462 -uo so -28 18' I9I 440 5 I9 1 .06 49 -108 I6' -26 o 192 430 8 3I 2 .25 162 -1os 38' -27 56' I93 430 35 66 3 12 330 104 16' -25 55' I94 430 3 8 1 .07 23 -109 45' 26 51' I95 430 27 79 3 .15 192 -Ios I9' -27 55' 196 430 20 57 2 .OS 292 -1o5 58' -25 3 7 197 430 17 38 2 15 466 -110 35' -28 40' 198 430 I3 29 2 13 210 -107 17' -28 14' 199 430 3 7 I .09 207 -107 29' 28 18' 200 420 15 31 1 .24 317 -104 25' -26 32' 201 420 28 45 2 11 137 -109 32' -28 26' 202 420 11 34 2 .09 368 -106 35' -28 4' 203 420 13 20 I .09 374 -106 I3' -27 53' 204 420 49 59 2 .06 267 -106 52' 26 o 205 420 10 36 2 .05 509 -no 48' -27 4 7' 206 420 5 20 1 .08 472 -no 2' -28 51' 207 420 48 85 2 .06 116

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APPENDIX 2 (Continued) Reference Longitude, Latitude, Height Height, Volume Basal Cross-Flatness "E "N Ranking m km) Are a, km 1 sectional (Summit: Area, Basal kml Axis) 151 109" 5' -28 5 208 420 25 54 2 14 221 -107 54' -27 40' 209 420 70 65 3 .07 262 -107 51' -26 2' 210 420 3 12 1 .08 389 -106 5' -27 40' 211 420 32 62 2 .02 352 -106"41' -27" 16' 212 410 10 19 1 10 510 -112 37' -26 29' 2 13 410 118 146 3 .09 479 -110 o -28 31 214 410 31 57 2 .28 177 -108" 18 -27 1' 215 410 28 66 3 11 176 -108 22' -27 7 216 410 9 23 1 .10 320 -104 0' -26" 43' 217 410 33 62 3 .03 321 104" s -26 40' 218 410 27 55 2 .09 396 -105 57' -27 32' 219 410 14 22 1 11 57 -108 26' -26 56' 220 4 1 0 10 23 1 .09 26 -108 48' -26 39' 221 410 11 31 2 05 270 -106 19 -25" 46' 222 410 24 65 2 .04 376 106 9' -27 44' 223 400 13 26 2 .06 136 -109"31' -28" 13 224 400 8 16 1 .18 16 -109 25' -26 45' 225 400 44 110 3 23 65 -107 50' -26 36' 226 400 43 103 3 .07 100 -107 39' 25 48' 227 400 33 160 4 .44 178 108 19' -27"11' 228 400 9 22 1 .45 155 109 11' -27 32' 229 390 6 15 1 .10 338 -104 11' -25" 30' 230 390 7 26 1 11 174 -108 40' 27" 28 231 390 38 60 2 11 433 -112 43' -28 41' 232 390 65 96 3 12 369 -106 36' -27" 58 233 390 18 27 1 17 189 108 20' -27" 39' 234 390 40 52 2 .19 161 -108 46' 27 53' 235 380 24 40 2 .29 395 -105 53' 27 38 236 380 11 16 1 31 35 -109 3 -26 25' 237 370 1 12 1 .22 159 -108 47' 27 48' 238 370 4 14 1 .23 54 -108 11 -26" 23 239 370 3 16 1 .22 340 -104" o 25 40' 240 370 7 16 1 .19 86 -107 24' 26 4 241 360 92 222 1 .24 441 -111 46' -27" 52' 242 360 66 115 2 14 308 -104 58' -26 14' 243 360 7 15 1 13 264 -108 1 -28 20' 244 360 10 36 1 .08 414 -105 16 27 20' 245 360 9 19 1 14 366 -106 45' -27 59' 246 360 28 42 2 .08 15 -109 15 -26 3 7' 247 360 1 1 27 1 .42 48 108 20' -26 8 248 360 1 5 1 18 201 -108 16 -28 29' 249 360 7 20 1 .07 205 -107 36' -28 25' 250 360 20 47 2 17 103 -108 9 -24 59' 251 360 1 49 2 .16 233 107 30' -27 o 252 350 10 12 1 19 32 108 52' -26 23 253 350 6 17 1 11 448 -111 15 -27 26' 254 350 11 31 1 18 519 -111" 46' 27 3 255 350 118 135 2 12 70 -107 50' -26 29' 256 350 8 19 1 .24 156 -109 5 27 31' 257 350 19 36 2 .05 163 -108 37' -27 51' 258 350 43 70 2 .30 561 -111" 24' 27 4' 259 350 17 23 1 .08 117

PAGE 130

APPENDIX 2 (Continued) Reference Longitude, Latitude, Height Height, Volume, Basal Cross-Flatness "E "N Ranking m km' Area, kmz sectional (Summit: Area, Basal kmz Axis) 403 -105 52' -27 24' 260 350 30 38 1 0 11 164 -108 34' -27 59' 261 350 8 15 1 17 45 -108 25 -25 59' 262 350 4 16 1 11 223 -107 48' -27 39' 263 340 37 35 2 .06 334 -104 13' -25 50' 264 340 34 64 2 .05 333 -104 11' -25 4 7' 265 340 29 54 2 .03 545 -110 6' -26 45' 266 340 9 28 1 .24 364 -106 49' 28 8' 267 340 14 39 1 .05 216 -107 57' -27 54' 268 340 15 45 2 13 142 -109 17' -28 3. 269 340 I2 26 1 .2I 165 -108 37' -28 3' 270 340 6 I3 1 18 145 -109 I8' 27 49' 27I 340 5 1 1 1 .26 367 -106 4I' -27 59' 272 340 32 44 2 .08 253 -107 I9' -28 1 273 330 16 43 2 .07 473 -110 5' -28 48' 274 330 6 1 I 1 15 445 -111 36' -27 16' 275 330 26 35 2 .10 426 -112 23' -27 22' 276 330 19 3I 2 .10 309 -104 49' -26 I 0' 277 330 4 12 I 13 559 -112 29' -28 I3' 278 320 5 13 1 .08 329 -104 12' -25 57 279 320 5 16 1 .09 387 -106 3' -27 11' 280 320 5 14 1 .10 381 -106 31' -27 28' 281 320 12 I8 1 .27 113 -109 59' 27 I7' 282 320 10 17 1 13 230 -107 52' -27 8 283 320 30 49 1 .06 385 -106 9' -27 13' 284 320 4 13 1 .07 14 -109 24' -26 38 285 320 30 83 2 .57 419 -10 8 59' -28 12' 286 320 4 10 1 12 259 -108 31' -26 6' 287 320 2 17 1 .05 302 -105 1 -25 51 288 320 9 24 1 .05 52 -108 21 -26 22' 289 320 5 14 1 .04 94 -107 50' -26 o 290 320 1 6 1 14 305 -104 49' -25 48' 291 320 7 16 1 .09 471 -110 6 -28 57' 292 310 7 16 1 .09 354 -106 59' -27 33' 293 310 4 11 1 .38 406 -105 36' -27 24' 294 31 0 7 14 1 .09 271 106 17 -26 3 295 310 17 42 1 0 11 19 109 0' -26 47' 296 310 3 9 1 .06 470 -110 15 -28 so 297 310 9 22 1 12 3 5 3 106 40' -27 23 298 310 19 29 1 .05 4 -109 31 -26 14' 299 310 30 95 2 13 3 -109 30' -26 8' 300 310 15 57 2 .28 290 -105 38' -25 49' 301 310 33 64 I 15 392 -105 58' -27 42' 302 300 8 10 1 .09 298 -105 24' -26 5' 303 300 5 11 1 .19 263 -107 57' -25 59' 304 300 3 13 1 .25 435 -112 1. -28 21 305 300 62 139 2 .25 468 -110 23. 28 so 306 300 4 13 1 .27 167 -108 30' -28 6 307 300 13 26 1 .28 114 -109 58' -27 25' 308 290 22 51 1 13 254 -107 18 -28 8' 309 290 15 43 1 .26 348 -105 2 -26 1 o 310 290 5 15 1 .26 193 -108 18 -28 o 311 290 3 10 1 .38 118

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APPENDIX 2 (Continued) Reference Longitude, Latitude, Heigbt Heigbt, Volume Basal Cross-Flatness "E "N Ranking m km) Area, km1 sectional (Summit : Area, Basal kml Axis) 22 -109 52' -26 50' 312 290 3 12 1 .32 108 -108 40' -27 6' 313 290 59 134 2 .08 500 -110 5' -27 29' 314 290 178 293 4 .18 422 -112 47' -27 18 315 290 70 118 3 .10 350 -104 31 -26 5' 316 290 7 20 1 .27 260 -109 28' -26 45' 317 290 4 11 1 .43 9 109 14' -26 19' 318 290 18 56 2 18 8 -109 7' -26 1 7' 319 290 5 15 1 .30 363 -106 47' -28 3' 320 280 12 30 1 .28 328 104 1' -25 53' 321 280 23 51 1 18 475 -110 6' -28 38' 322 280 23 45 1 13 391 -106 5 -27 53' 323 280 71 74 1 .22 146 -109 13 -27 45' 324 280 5 10 1 .39 21 -109 50' -26 47' 325 280 1 1 39 1 19 429 -112 30' -28 6 326 270 13 38 1 25 92 -107 29' -26 1' 327 270 8 29 1 .20 416 -105 29 27 5 328 270 21 41 1 18 523 -111 12 26 12 329 270 1 1 28 1 .15 53 -108 12 -26 19 330 270 5 23 I .37 118 -109 41' -27 43' 331 270 16 29 1 14 199 -108 2' -28 15 332 270 13 49 1 .07 191 -108 18' -27 43' 333 260 4 5 0 21 528 -111 15 -26 33 334 260 6 15 1 11 242 -107 0' -27 8' 335 260 15 37 1 .27 478 -110 25 -28 36' 336 260 4 10 1 11 18 -109 0' -26 3 7' 337 260 10 31 1 .38 356 -106 58' -27 38' 338 260 6 18 1 15 300 -105 1' -26 7' 339 260 8 24 1 .20 337 -104 17' -25 38' 340 260 2 14 1 .09 249 -107 21' -27 46' 341 260 8 14 I .17 150 -10 9 0' -27 53' 342 250 5 1 1 1 .25 289 -105 39' -25 58 343 250 38 76 2 15 557 -110 36' -26 34' 344 250 2 8 I .33 46 108 22' -25 55 345 250 3 18 I .42 294 -105 55' 25 3 1 346 250 6 19 1 .32 357 -106 54' -27 44' 347 250 6 15 1 19 278 -105 49' -26 2' 348 250 7 22 1 .12 95 -107 48' -26 1' 349 240 5 27 1 11 101 -107 56' -25 6' 350 240 6 39 1 19 91 -107 43' -26 7' 351 240 4 15 1 .03 313 105 16' -26 47' 352 240 2 5 0 13 225 107 33' 27 39' 353 240 31 30 1 13 33 -108 53' -26 19' 354 240 4 16 I .05 306 -104 47' -25 42' 355 240 9 18 1 17 272 -106 27' -26 8' 356 230 3 9 1 .12 31 -108 51' -26 28' 357 230 4 21 1 15 123 -109 57' 27 54' 358 230 1 7 39 1 25 128 -109 37' -28 4' 359 230 7 14 1 .08 413 -104 58' -27 31' 360 230 4 14 1 .07 122 -109 53' -27 53' 361 230 7 11 1 .34 331 -104 14' -26 2 362 230 16 34 1 14 39 -108 51 -26 1' 363 230 2 6 0 .20 119

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APPENDIX 2 (Continued) Reference Longitude Latitude, Height Height Volume, Basal Cross-Flatness "E "N Ranking m km) Area, km1 sectional (Summit: Area, Basal kml Axis) 85 -107 20' -2 6 I 0 364 220 II 28 1 .07 157 -109 1 -27 29' 365 220 5 9 0 19 51 -los 16' -26 1 7' 366 220 10 29 1 16 304 -104 52' -25 4 7' 367 220 18 43 1 .05 531 -111 0' -26 46' 368 220 6 13 1 .49 390 -106 1' -27 37' 369 220 3 7 0 1 0 517 -11P 51' -27 13' 370 220 40 52 1 1 0 168 -los 27' -28 3 371 220 5 12 1 .26 24 -109 32' -26 51 372 220 4 13 1 12 388 -106 10' -27 29' 373 210 2 7 0 .27 526 -111 14 -26 32' 374 210 3 8 1 .20 138 -109 16' -28 25' 375 210 32 63 1 .38 458 -110 6' -28 55' 376 200 32 81 1 .07 112 -109 53' 27 1 0' 377 200 4 14 1 .12 307 -104 46' -25 57' 378 200 12 25 1 .08 133 -109 48' -28 26' 379 200 22 39 1 .49 431 -112 16' -28 3' 380 200 13 36 1 .02 141 -109 23' -27 59' 381 200 13 23 1 .28 524 -111 12' -26 18' 382 200 5 12 0 41 2 -109 38' -26 21' 383 200 1 6 0 .50 120

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APPENDIX 2 (Continued) Reference Slope Summit Summit Trend Basal Basa l Aspect Trend degrees Long Short Summit Long Short Ratio Basal Ax is, km Axis, km Long Axis, Axis, km Axis, km (Long Long degrees Axis : Axis, Short degrees Axis 287 9 31 0.28 0.27 7 65.09 40.54 1.61 75 106 8 .14 23.61 11.37 67 97. 96 57. 23 1. 71 65 383 7 .05 8.43 1.77 74 69.86 50.11 1.39 158 274 7 .95 2.55 1.50 74 66.65 43.61 1.53 69 326 8 .74 0.64 0 57 93 53.62 37.50 1.43 2 286 7 .62 1.91 0.92 90 46.60 41.89 1. 11 1 279 10.83 0 .54 0 .38 73 50.97 29.02 1.76 86 311 11.22 1.80 0 .82 73 39.81 27 03 1.47 103 283 8.56 1.57 0 .95 159 36.31 35. 38 1.03 64 312 7 17 1.33 0 .66 172 48.48 40. 59 1.19 142 105 12 .75 1.85 1.17 78 33. 29 23. 09 1.44 172 280 11. 87 0 .50 0 .39 52 25. 34 23.33 1.09 34 379 8 .80 0 .35 0 .28 174 31.83 29. 35 1.08 150 418 6 .67 4 19 1.34 5 58.04 37. 09 1.56 141 410 11.17 1.98 1.66 174 34. 87 22. 12 1.58 165 252 15 .8 1 1.16 0 .78 104 20.62 14. 41 1.43 174 384 8.58 0.53 0.36 88 29.09 25.94 1.12 173 79 7 .47 5.03 1.29 78 57.91 30. 27 1.91 85 501 8.11 4.42 3 .90 79 33.84 29. 18 1.16 175 393 13 17 4.51 2 41 75 22.95 17.71 1.30 171 175 14.52 3.57 2.07 147 27 .80 15.35 1.81 50 544 4 61 0 .45 0 .29 6 52.11 42. 73 1.22 128 285 6.53 0.40 0.29 84 43.60 28. 78 1.51 77 407 11.05 2.03 1.87 83 22 .11 18 36 1.20 173 325 12 .40 0.41 0 .35 62 28 16 14 .91 1.89 18 80 7.54 2 .84 2 28 167 29.79 26.29 1.13 70 111 9 .85 1.85 1.20 118 21.33 18 .49 1.15 1 21 284 7.32 0 .68 0 .38 56 36.34 23.42 1.55 68 88 8.84 1.17 0.48 75 24.36 19 38 1.26 100 77 6 91 0 .99 0 87 43 31.92 24. 31 1.31 71 498 10 15 0.48 0 .47 74 26.80 16.21 1.65 173 417 8.41 2 .04 0 .92 95 33.37 19 .99 1.67 123 336 5 89 0 .79 0 .78 6 29.80 27. 75 1.07 139 564 8 83 4.06 2 .20 164 28 .92 19.58 1.48 65 562 9 .53 0 .49 0 .48 162 31.26 16 .57 1.89 68 380 7 .07 1.05 0.56 178 27.61 22.31 1.24 62 17 8.47 0 .70 0 .48 49 32. 25 18.62 1. 73 46 451 8 .77 2 .32 1 .97 65 31.67 19.33 1.64 163 186 7.55 0 .97 0 .50 14 36.65 20.71 1.77 39 349 5.60 0.88 0.61 173 47.01 27.54 1. 71 96 228 5.66 1.19 0 .72 50 29 08 27. 35 1.06 14 6 499 4.98 0.81 0 .52 96 44. 43 30.39 1.46 96 281 14.95 1.33 1.18 63 12 .06 10.62 1.14 164 282 6.75 2 .83 0 .78 66 28 .95 21.57 1.34 64 89 14 .60 0 .39 0.24 49 13.29 9.69 1.37 75 405 10 .24 0 .76 0 .46 1 1 19.77 13.97 1.42 74 495 4 .49 0 .42 0 .33 177 31 .88 31.38 1.02 56 143 5.22 4.54 1.79 73 31.21 28.28 1.10 76 323 8 .47 0.92 0 .35 89 28 .67 16.60 1.73 66 335 5 .86 1.13 0 .78 176 29 .56 22.42 1.32 57 238 7 .74 3.37 2 .6 0 1 61 22.64 18.92 1.20 163 121

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APPENDIX 2 (Continued) Reference Slope, Summit Summit Trend Basal Basal Aspect Trend degrees Long Short Summit Long Short Ratio Basal Axis, km Axis km Long Axis, Axis, km Axis km (Long Long deg r ees Axis : Axis Short degrees Axis 196 7 .64 1.78 0 77 75 33.44 17 .32 1.93 103 515 16.64 1.38 0.87 103 11.13 8 24 1.35 144 529 32.93 0.36 0.34 105 4 37 3.68 1.19 95 30 5.64 0.54 0.28 162 29.51 22.17 1.33 116 104 13.24 12 .6 1 8 28 1 63 31 39 17 .04 1.84 164 220 15.47 1.94 1.09 133 10.45 8.46 1.23 133 543 7.26 0.45 0 28 127 24.60 16 13 1.52 31 237 12.40 1.77 1.59 1 18 31 10. 68 1. 7 1 30 453 5 .22 2.00 1.03 169 37.40 22.91 1.63 170 83 6 .67 1.17 0 .50 172 32.33 17 27 1.87 140 219 10 .85 0 .96 0 61 4 14.17 10 73 1.32 154 239 9 23 1.17 0 85 13 22.47 12 66 1.77 136 424 5 73 2 25 1.02 80 20. 82 19 35 1.08 155 245 6 .84 3.07 1.55 160 23. 79 16 88 1.41 124 98 14 .60 2.63 1.61 117 12 75 8 68 1.47 114 314 5 71 0.84 0 53 173 32.21 18.73 1.72 Ill 411 14 93 1.18 1.07 6 9.10 7.60 1.20 38 76 5 .62 5.78 2 13 33 26 72 19.82 1.35 73 486 9.89 2.34 2 12 179 17. 12 12.10 1.41 123 182 17.08 1.38 0 .82 69 7 31 6.42 1. 14 23 341 13.14 4 .04 3 21 65 19.84 10.49 1.89 60 67 6.48 1.90 1.70 86 31 .00 1 6 67 1.86 76 276 6.14 0.84 0 .72 3 30. 93 16 35 1.89 1 346 14 .3 5 0.58 0 .42 26 11.58 6.99 1.66 21 212 8 .50 1.10 0 .62 175 22 .66 11.73 1.93 118 339 6 .02 0.37 0 .29 79 20.17 15 66 1.29 92 125 7 .44 1.49 0 .68 54 22. 55 13 09 1.72 50 443 7 19 0.38 0 .36 33 13. 27 13 .20 1.00 6 4 217 13.50 1.04 0 .80 97 9 .56 7 .46 1.28 100 251 9 51 1.48 1.24 58 12 09 10. 55 1.15 129 246 12.41 1.94 1. 75 106 13. 13 8 65 1.52 122 428 9.65 1.60 1.13 63 12 .70 1 0 07 1.26 25 268 7 .78 0 .92 0 .63 75 23.48 11.76 2 .00 138 248 6 .94 2 .40 1.91 72 27. 39 14.24 1.92 52 275 8 .46 1.46 1.27 90 22. 05 11.22 1.97 25 488 13.29 0.54 0.45 109 8 78 6 4 6 1.36 29 401 7 61 1.23 0 .84 0 12 4 3 11.46 1.08 118 492 8 .38 1.03 0.39 10 16 49 9.89 1.67 45 247 5 .78 1.62 0 82 167 18.20 14.65 1.24 61 450 8.79 3.50 0.79 12 3 19.39 9.84 1.97 132 504 10.04 4.66 4 .60 175 12 .96 12 .40 1.05 177 372 10 .34 0.47 0.39 0 13. 79 7 .96 1.73 159 548 7 85 0.71 0 27 170 11.00 10 29 1.07 31 415 5 .70 4 .36 1.11 20 28 10 14 .74 1.91 72 256 5 .59 2 .72 2 .48 152 22. 63 16 38 1.38 63 75 5 .80 1.49 1.21 180 16 .49 14.40 1.15 117 552 10 .33 1.09 0 .90 176 15 84 8.14 1.95 20 121 10 .20 1.08 1.04 114 13 .04 8.26 1.58 26 310 15 .08 1.06 0 .72 176 9 51 5.47 1.74 2 78 7 .55 2 .00 1.63 67 1 9 69 11.29 1. 74 93 549 6 .93 0 .89 0 .59 1 75 11.66 11.12 1.05 63 93 8 .04 0.42 0 .40 177 1 3 .25 9.32 1.42 97 122

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APPENDIX 2 (Continued) Reference Slope Summit Summit Trend Basal Basal Aspect Trend degrees Long Short Summ i t Long Short Ratio Basal Axis k.m Axis k.m Long Axis Axis. k.m Axis k.m (Long Long degrees Ax i s : Axis Short degrees X 412 16 .09 0 .48 0 .47 172 6 72 4 .84 1.39 5 61 8 91 0.77 0 75 63 9 93 8 .79 1.13 58 183 21.30 1.06 0 .52 172 4 87 3 .75 1.30 165 563 5 .66 2 17 1.40 147 17 27 14 .11 1.22 67 62 9 .70 0 .47 0 .47 72 11.30 7 .72 1.46 172 102 7.34 0.26 0 .26 146 12.22 9 .88 1.24 103 204 11.97 0 31 0.26 165 9 59 6 01 1.59 170 491 10.68 2 .54 1.26 170 9 23 7.73 1.19 175 547 16 .40 0 22 0 .20 85 5.16 4 35 1.19 56 318 8 .69 1.09 0 .68 176 11. 47 8 53 1.34 18 490 9 .68 1.52 1.46 104 10.16 8 .49 1.20 30 222 17 .12 0 .48 0 .34 72 5 76 4 17 1.38 127 556 9 .47 1.47 1.47 179 10. 53 8 .54 1. 23 49 291 27 .39 0 .82 0 .44 165 5 .09 2 .72 1.88 165 4$0 14 .42 2 .30 1.23 81 7 .90 5 81 1.36 2 540 8 .73 1.91 0 .75 92 9 .21 8 .43 1 .09 158 227 5 .16 2 .45 1.59 11 21 .04 14 67 1.43 10 265 10. 21 3 .36 1.75 49 9 77 8 19 1.19 147 542 10. 73 1.94 0 .96 25 12 29 7.08 1.74 28 116 5.72 1.77 1.20 39 15 05 12.78 1.18 39 84 19.57 1.14 0 77 157 7 35 4 .03 1.82 15 206 13 .53 0 88 0.30 78 7 .40 5 12 1 45 60 195 5 .39 1.61 1.32 179 19.25 13 39 1.44 59 322 6 71 0 71 0 .58 99 20. 05 10. 26 1.95 26 69 14 .11 0 .69 0.53 58 7 05 5 .07 1.39 144 489 14 .34 0 .69 0 .29 13 6 83 4 .67 1.46 13 197 7 .86 0 81 0 63 169 9 03 8 .74 1.03 139 173 7 13 1.10 1.07 168 18 .50 10 03 1.84 107 47 7 .08 0 68 0 64 64 10 63 9 .50 1.12 39 398 3.97 1.62 1.30 0 17 63 17 14 1.03 80 342 12 .44 0 .32 0 13 83 5 43 5 .03 1.08 125 43 25 .05 2 .78 2 .45 40 4 .84 4 .72 1.02 47 226 4 .78 1.91 0.82 79 19 66 13 49 1.46 65 255 4 .86 0 .62 0 .52 73 20. 13 12 .98 1.55 37 214 15.51 0 .53 0 .40 68 5.20 4 22 1.23 168 404 8 .68 3 01 1.04 115 8 .74 7 .85 1.11 13 59 14 .49 0 41 0 .34 170 6 .76 4 .36 1.55 171 373 9 .03 0 .47 0 .29 12 10.49 6 71 1.56 9 211 14 .97 0 61 0 .30 25 4 35 4 .11 1.06 33 487 13 .37 0 .94 0 .35 174 5 14 4 .64 1.11 85 361 6 .36 1.47 1.18 4 15 43 10. 34 1.49 12 360 6.83 0 .65 0 .60 15 12 .09 9 12 1.33 159 382 9 .57 1.08 0 .56 1 6 65 6.62 1.00 13 558 6 41 0 .48 0 23 5 10.71 9 31 1.15 7 184 7 .37 0 .30 0 .29 82 9 12 8 18 1.12 81 96 14 .40 0 .36 0 21 175 6 02 4 18 1.44 38 493 12 .92 1.40 0 .38 7 9 .42 4 83 1.95 8 359 5 .94 3 .66 1.08 6 15 83 10 87 1.46 2 27 10 .80 0.72 0 .46 175 8 .82 5 .80 1.52 130 50 11.23 0 13 0 .05 30 8 .66 5 19 1.67 37 550 6 31 0 .66 0 .51 73 12 35 9 .56 1.29 125 188 17.62 1.35 0 73 177 6 .41 3 88 1.65 32 123

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APPENDIX 2 (C o ntinued) Reference Slope, Summit Summit Trend Basal Basal Aspect Trend deg r ees Long Short Summit Long Short Ratio Basal Axis, km Ax i s km Long Axi s, Axi s km Axis km ( Long Long degrees Axi s : Axis, Short degrees Axis 213 9 .30 0.87 0 .80 3 13.20 6 91 1.91 94 400 6 .90 0 .46 0 .45 83 9.65 8 71 1.11 1 1 55 12.19 2 .26 1.42 1 3 3 6 .41 5 .9 6 1.08 138 81 5 61 0 .75 0 31 84 13 .39 10. 28 1.30 78 194 11.10 1.81 0 66 139 5 74 5 66 1.02 54 90 20.63 0.92 0 .76 71 4 .21 3 .36 1.25 78 60 6 .89 1.50 0 .56 0 9 93 8.67 1.15 174 209 20.80 0.97 0 83 147 5 .36 3 41 1.57 147 72 19.14 1. 71 1. 11 158 5 75 3.93 1.46 49 496 16.14 2.61 1.23 165 8 1 0 4 .55 1. 7 8 157 535 6 .96 4.49 2 .94 107 20.86 10.80 1.93 127 200 16.51 .1 .24 0 .46 165 6 2 1 3 .70 1.68 148 135 7 .29 1.25 0 .59 56 15. 4 1 7 .94 1.94 41 378 8 .16 0 .66 0 .54 174 1 2. 19 7 .10 1.72 169 97 14.00 0 .25 0 25 97 6 .35 4 .02 1.5 8 119 56 13 .33 1.54 1.24 72 7 64 5 21 1.4 7 76 288 20. 2 1 0 .78 0 .59 179 4 .04 3 15 1.28 162 343 7 .45 0 .84 0 81 70 11.01 7 .8 5 1.40 34 64 7 .24 3 .32 3 1 0 46 18 .33 10.34 1.77 40 351 7 1 7 0 .40 0 .35 7 12 .61 7 .67 1.64 155 497 10.16 0 .80 0 7 6 7 5 99 5 .89 1.02 93 250 14.29 1.31 0.91 5 6.45 4 .52 1.43 155 66 7 67 1. 78 0 .96 136 1 3 51 7 .65 1.77 133 319 7 .30 0 .78 0 .41 1 7 60 7 .44 1.02 114 244 16.69 0 .75 0 65 180 4 39 3.65 1.20 1 13 5 13 6 .97 2.27 2 .00 161 12 .33 9.36 1.32 163 131 8 .22 1. 11 0 75 3 8. 11 6 .98 1.16 2 481 10.76 0 .83 0 .58 3 6 72 5 21 1.29 4 516 6 21 1.14 1.07 20 12.75 9 .15 1.39 167 560 5 21 1.22 0 81 167 17.86 10.45 1. 7 1 142 261 9 .40 0 .94 0 .59 52 6.28 5 91 1.06 147 82 12.60 1.63 1.60 48 5 .77 5 .54 1.04 144 243 6 .83 0 .98 0 .89 79 12. 83 8 .24 1.56 2 5 0 6 4 .53 0 .58 0 .37 178 20. 14 11.46 1. 76 144 99 6 .32 1. 4 6 0 .64 100 13 68 8 .59 1.59 98 462 14.52 0 .48 0 19 1 7 14 3 5 9 1.99 9 4 9 10.44 1.73 1.48 43 6 .85 6 15 1.11 46 162 6 .84 1.24 0 .96 145 10.36 8 13 1.27 148 330 15 0 0 0 .28 0 22 84 3 .52 3 .43 1.03 126 23 6 .60 1.50 1.50 21 1 0 .55 8 93 1.18 14 192 7 .70 0 .46 0 43 170 11 4 4 6.79 1.68 149 292 9 .87 1.46 0 66 87 8 16 5 .60 1.46 88 466 10.29 1.05 0 .59 17 7 .70 5.33 1.44 12 210 13.64 0 .39 0 .36 177 4 .09 3 .90 1.05 66 207 13.83 1.55 1.43 75 7 83 4 .84 1. 6 2 72 3 1 7 9 .52 1.04 0 .60 99 9 .09 5.61 1.62 23 137 7 7 7 0 .73 0 .49 51 7 19 6 .64 1.08 122 368 12. 2 1 0 .49 0 .44 1 5 .90 4 .32 1.37 158 374 6 .82 0 .56 0 .47 179 10. 91 7 .49 1.46 7 1 267 9 .83 0 .40 0 .36 86 9.41 5 2 1 1.81 29 5 0 9 13. 71 0 .57 0 25 178 7 13 3 .69 1.93 8 472 7 .49 0 61 0 61 107 1 1.97 6 .99 1. 71 139 124

PAGE 137

APPENDIX 2 (Continued) Refere nce Slope, Summit Summit Trend Basal Basal Aspect Trend degrees Long Sh o rt Summit Long Short Ratio Basal Axis, lun Axis, lun Long Axis Axis. lun Axis lun ( Long Long degrees Axis : Axis, Short degrees Axi s 151 7.07 1.33 1.09 79 9 .92 7 .86 1.26 173 221 5.69 0.66 0 .58 174 9 67 9 .02 1.07 119 262 14 .93 0 .33 0 31 15 4 .82 3 .46 1.39 120 389 7.24 0 .24 0 18 69 12 .46 6 .79 1.84 146 352 12 .65 0 51 0 .44 0 5.72 4 .09 1.40 179 510 5 .25 1.83 0 .70 176 18. 79 9.61 1.95 1 479 9.86 2 .80 2 01 I 10. 28 6 73 1.53 40 177 5.52 1.87 0 .62 172 12 97 9 .11 1.42 175 176 11.04 0 73 0 .44 41 6 58 4 64 1.42 42 320 5 .80 0 .36 0 31 2 10 .90 8 .38 1.30 42 321 7.30 0 .92 0 .66 174 10. 07 7 .06 1.43 61 396 13.00 0 .75 0 51 11 7 10 4 .07 1.75 164 57 11.43 0 .49 0 .37 117 5 .32 4 .43 1.20 123 26 9.90 0.39 0 .29 178 8 35 4 .99 1.67 2 270 8 .06 0 .37 0 .34 91 11.61 6 13 1.89 124 376 9 .47 0 .40 0 .32 3 6 77 5.12 1.32 159 136 12 .26 0 .99 0 .70 175 4 78 4.38 1.09 3 16 6 .72 2.78 2 .35 24 13.18 9 14 1.44 120 65 5.81 0.98 0 .72 4 14.28 8 58 1.66 8 100 5 .32 7.30 5 88 20 15.82 14 46 1.09 18 178 17.44 2.31 2 18 147 5 .19 4.73 1.10 147 155 14 .43 0 5 7 0 .36 4 6 37 3 .39 1.88 10 338 9 .80 0.92 0 .35 1 6.73 4 86 1.38 177 174 5.80 0.99 0 .98 65 9 .60 8 65 I. 11 61 433 4.20 1.94 0 .99 160 12 .34 11.62 1.06 119 369 13 .09 1.38 0 68 11 7.75 4.04 1.92 4 189 6 .27 1.94 1.83 17 8 10.40 8 .93 1.17 142 161 7 .90 2 .72 1.63 120 8 08 7 10 1.14 32 395 12 .48 1.89 1.07 174 4 97 4 51 1.10 I 35 14 .26 1.07 0 83 149 4 .76 3 .74 1.27 52 159 17.42 1.05 1.00 105 5 57 3 .36 1.66 130 54 1 3 .53 1.06 0 .96 II 5 .13 4 .04 1.27 I 340 12 .02 1.00 0 .74 86 5 .01 4 .22 1.19 122 86 10 .50 2 15 0 .90 72 7.86 4 .78 1.65 76 441 6 .04 1.85 1.67 79 16 08 8 .47 1.90 26 308 13 .54 0 .72 0 .42 6 5.20 3 41 !.53 179 264 8 .32 0.71 0 .52 168 9 57 5 .45 1.76 !58 414 11.95 0 .74 0 65 171 6 12 4 .05 !.51 153 366 6 .66 0 .62 0 .58 1 65 7 87 6.74 1.17 146 15 11.69 2 .64 2 .46 96 6 13 5 .94 1.03 93 48 20.97 0.55 0 .37 4 2 .96 2 25 1.31 177 201 11.32 0.47 0 17 2 5 57 3 .76 1.48 74 205 7 .35 1.53 1.20 71 8 93 6 78 1.32 170 103 7.19 1.39 1.29 32 10 .24 7 .00 1.46 139 233 12 .40 0 .87 0 67 1 65 4 .11 3 85 1.07 158 32 13 .13 0 .59 0 .45 13 5 65 3.45 1.64 76 448 8 27 1.62 0 .74 144 7 87 5.55 1.42 145 519 5 .62 1.41 1.20 9 1 4 1 6 8 31 1.70 161 70 21 .08 0 73 0 5 8 53 3 10 2 .39 1.30 69 156 5 62 0.49 0 .35 168 7 .76 7.46 1.04 20 163 6 .08 5 03 1.33 10 9 1 3 15 7 91 1.66 103 561 11.29 0 .42 0 .42 167 6 63 3 .92 1.69 14 125

PAGE 138

APPENDIX 2 (Continued) Reference Slope, Summit Summit Trend Basal Basal Aspect Trend degrees Long Short Summit Long Sh o rt Ratio Basal Axis, km Axis, km Long Axis, Axis km Axis, km (Long Long degrees Axis: Axis, Short degrees Axis 403 8 .46 0 .79 0 .73 2 8 .98 5 .44 1.65 142 164 13 28 0.79 0 .72 115 5 .30 3 68 1.44 10 45 11.86 0 .53 0.47 42 5.66 3 .80 1.49 165 223 6 25 0 .53 0 .32 5 6 71 6 .53 1.03 1 11 334 6 .22 0 .57 0.40 179 12 .75 6 .64 1.92 34 333 6 .27 0 31 0 .30 85 11.49 6.49 1.77 0 545 9 .58 1.50 1.30 104 6 .56 5 .32 1.23 117 364 6 .95 0 .40 0.20 176 7 21 5.77 1.25 22 216 6 31 1.36 0 .73 107 9 18 6.88 1.33 131 142 11.47 1.59 0.93 178 7 71 4 29 1.80 4 165 11.36 0 .84 0 65 173 4 .08 4 .03 1.01 162 145 15 .07 1.10 0 .86 8 4 .11 3 .39 1.21 14 367 5 71 0 .89 0.38 177 8 .29 7.18 1.15 66 253 6 19 0 61 0 .40 7 8 .49 6 48 1.31 11 1 473 13 .36 0 .57 0 .53 62 4 17 3 .30 1.26 55 445 6 31 0 81 0 .59 75 7 35 6.56 1.12 66 426 6 .35 0 81 0 .48 165 6.70 6.41 1.05 5 309 13 .30 0.59 0 .47 169 4 .74 3 26 1.45 15 559 12.48 0 .42 0 27 1 5 .26 3 16 1.66 10 329 9 .97 0 .45 0 .42 178 5 .60 4 .07 1.38 160 387 11.26 0 .68 0.40 0 6 83 3 .61 1.89 7 381 15.59 1.36 1.25 63 6 10 3 .55 1.72 32 113 10.67 0 .65 0 .61 32 5 .60 4.01 1.40 38 230 6 .78 0 .62 0 .47 97 11.64 5 85 1.99 61 385 10.09 0 .33 0 .30 11 4 .59 3 .90 1.18 131 14 8 .84 8.41 4 .22 27 13 .95 8.34 1.67 9 419 11.48 0 .48 0 .37 153 3 71 3 53 1.05 55 259 11.03 0 .22 0 21 41 5 86 3 .50 1.68 22 302 6 31 0 .30 0 27 3 6 35 6 .06 1.05 8 52 10 .44 0.21 0 16 35 4 .84 3 64 1.33 33 94 17 .43 0 51 0 .30 88 3.59 2.34 1.54 57 305 9.57 0 .50 0 .39 78 5 .80 4 19 1.38 38 471 8 .27 0 .50 0 .29 175 4 65 4 .56 1.02 84 354 19.66 1.32 1.30 114 3 .80 3 .03 1.25 126 406 10 .26 0 .38 0.35 8 4 39 3 .77 1.16 61 271 6 61 0 .95 0 69 88 9 35 6 .04 1.55 148 19 15 .79 0.24 0 18 89 4 .52 2 .37 1.91 15 470 9 .08 0 .89 0 .38 167 6 53 4 .26 1.53 171 353 7.62 0 .36 0 29 177 8 03 4 .92 1.63 132 4 4 01 2 .00 1.04 1 1 12 .70 9 88 1.29 1 3 5 .33 4 41 1.05 159 11. 63 7 .69 1.51 176 290 6 .59 1.77 1.13 178 12 .36 6 .50 1.90 168 392 10 .20 0 .39 0 29 168 4 17 3 .62 1.15 165 298 11.66 0 .89 0 .50 160 3 .78 3 41 1.11 169 263 12 .87 1.05 0 .94 9 4 .56 3 .57 1.28 21 435 3 .86 4 .59 2 .02 177 15 75 10 .92 1.44 42 468 12 .26 1.46 0 86 172 4 85 3 .62 1.34 172 167 11.13 1 88 1.28 80 6 .96 4 33 1.61 169 114 6 .07 1.69 0 .39 30 9 84 5 85 1.68 133 254 9 14 2 19 1.51 4 9 .06 5 12 1.77 6 348 10.55 1.47 0 .94 175 5 27 4 .06 1.30 170 193 13 .52 1.53 1.32 3 3 .78 3 73 1.01 101 126

PAGE 139

APPENDIX 2 (Continued) Reference Slope, Summit Summit Trend Basal Basal Aspect Trend degrees Long Short Summit Long Short Ratio Basal Axis, km Axis, km Long Axis, Axis km Axis, km (Long Long degrees Axis : Axis Short degrees Ax i s 22 14 .00 1.36 1.14 172 4 .35 3.47 1.25 62 108 3.67 1.14 1.01 28 16 .38 10 .06 1.63 120 500 2.40 3 .47 3 .39 6 20.11 17.22 1.17 94 422 2 .72 1.49 1.20 69 13 .44 13.41 1.00 159 350 10 16 1.71 1.19 180 6 .44 4.42 1.46 167 260 17 .96 1.68 1.55 175 4 .19 3 .34 1.26 93 9 4.89 1.85 1.46 142 10 17 8 .25 1.23 139 8 12 67 1.90 0 .76 7 5 .54 3 .34 1.66 0 363 12 .68 1.33 1.11 83 4 .99 3 .60 1.38 169 328 6 23 1.91 1.34 92 11.14 6 .46 1.72 136 475 5 61 1.00 0 78 95 7.47 6 .49 1.15 1 1 1 391 5.68 .2 .86 1.46 166 12 85 7 .09 1.81 167 146 20.43 1.48 1.48 93 4 .60 2 .98 1.54 86 21 7 .03 2 .38 0 .56 175 10 .09 5 10 1.98 168 429 8.17 2 .24 1.35 17 9 .00 5 .11 1.76 22 92 7 .57 1.30 0 .99 173 6 .44 5 .05 1.28 170 416 5 .15 1.54 1.26 177 8 .67 7 25 1.20 34 523 6 .40 0 .96 0 77 9 5 .98 5 .59 1.07 73 53 12 .53 2 10 2 .05 153 6 .78 4 .48 1.51 64 118 7 .18 1.19 0 .82 4 8.98 5 .11 1.76 129 199 4 51 0 .72 0 .40 167 8 33 7 25 1.15 106 191 16 .06 0 .62 0 .39 99 2 64 2 .20 1.20 143 528 8 .58 0 63 0.45 2 5 73 3 89 1.47 176 242 8 .57 2 05 1.70 141 8.97 5 15 1.74 42 478 12 .29 0 57 0 .29 1 4 95 2 68 1.85 167 18 8 .75 2 .38 2 35 57 6 .74 5 73 1.18 62 356 9 .47 0.69 0 .66 58 5 .44 3 .78 1.44 32 300 7.75 1.16 1.08 7 6.15 4.90 1.25 33 337 10 .37 0 .50 0.36 1 6 .11 3.20 1.91 29 249 11.79 0 91 0 .59 1 5 87 3 .08 1.91 19 150 8 .96 1.33 0 73 3 4 28 3 .90 1.10 8 289 3 .62 1.54 1.50 69 10 .30 9.41 1.10 162 557 14 .04 1.05 1.02 177 3 25 3 .02 1.08 178 46 12 .22 2 16 1.66 60 5 15 3 .97 1.30 77 294 8 .10 2 69 0 .58 160 6 23 4 .09 1.52 160 357 8 .44 1.07 0 .39 173 3 99 3.76 1.06 1 278 6 .85 0 88 0.55 169 6 87 4.72 1.46 176 95 5.49 0 .92 0 .50 175 7 52 5 .49 1.37 44 101 4 .80 1.59 0 .98 167 7.06 6 .70 1.05 73 91 7.37 0 19 0 .11 74 4 76 3 .82 1.25 77 313 13.90 0 .32 0 26 77 2 28 2 .20 1.04 176 225 6 .24 1.24 0 .60 8 8 83 4 .99 l. 77 32 33 6 .50 0 28 0 18 38 4 .84 4 .39 1.10 54 306 6 51 1.06 0 .77 171 5 .91 4 .98 1.19 136 272 9.12 0 .54 0 24 83 3 64 3 10 1.17 42 31 8.97 1.01 0 53 5 6 72 3 .44 1.95 173 123 5 .92 2.70 0 .91 52 9 .20 5 .34 1.72 6 128 9.35 0.39 0 .30 64 5 .17 3 .09 1.67 23 413 6 .72 0.34 0 25 96 4 25 4 .15 1.03 153 122 10 .93 !.55 1.16 78 4 48 3 .54 1.27 74 331 6 .85 0 .97 0 .95 74 8 73 4 .77 1.83 179 39 16 15 0 .70 0 .52 157 4.04 2 .11 1.92 158 127

PAGE 140

APPENDIX 2 (Continued) Reference Slope, Summit Summit Trend Bas al Basal A s pect Trend degree s Long Short Summit Long Short Ratio Basal Axis, k.m Axis k.m Long Axis ion ion ( Long Long degrees Axis, Short degrees A 85 7.27 0.33 0 29 169 5 .02 3 .74 1.34 58 157 11.42 0 78 0 58 112 4 25 2 75 1.54 24 51 5.48 1.16 1.02 113 8 06 5 61 1.44 46 304 4 .30 0 .39 0 .34 5 9 .51 6 .20 1.54 17 3 531 13 .57 2 .04 1.86 4 4 33 3 .68 1.18 86 390 12 19 0 .39 0 .25 177 4 26 2 29 1.86 168 517 5 16 0 .89 0 .79 103 10 58 5 .66 1.87 158 168 9.24 1.19 0 87 71 4 31 3 .57 1.21 134 24 9 31 0 .53 0 .53 2 5 .39 3 .22 1.68 137 388 12 .07 1.16 0 49 175 3 60 2.45 1.4 7 171 526 8 71 0 .82 0 65 8 3 83 3 .39 1.13 147 138 4 65 3 .90 3 .11 94 10 32 8 28 1.25 110 458 6.14 0 .32 0 .27 160 4 04 3 .98 1.01 88 112 7 .39 0 .57 0 .42 174 4 .99 3 51 1.42 79 307 5 .82 0 .46 0 .44 70 7 37 4 .36 1.69 2 133 6 .93 4 .14 1.91 2 7 21 5 .20 1.39 178 431 4 .05 0 15 0 14 62 8 .15 5 .79 1.41 17 9 141 6.94 1.65 1.19 174 5 .58 4 .48 1.25 16 3 524 9 .53 2 51 1.09 63 5 23 3 .47 1.51 57 2 17 .70 1.46 1.20 2 2.88 2 45 1.17 0 128


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