Geophysical Investigation of Flood-Induced Sinkhole Collapses, Lakewood Region, Eddy County, New Mexico

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Geophysical Investigation of Flood-Induced Sinkhole Collapses, Lakewood Region, Eddy County, New Mexico

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Geophysical Investigation of Flood-Induced Sinkhole Collapses, Lakewood Region, Eddy County, New Mexico
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National Cave and Karst Research Institute Report of Investigation 6
NCKRI Reports of Investigation
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NCKRI REPORT OF INVESTIGATION 6GEOPHYSICAL INVESTIGATION OF FLOOD-INDUCED SINKHOLE COLLAPSES, LAKEWOOD REGION, EDDY COUNTY, NEW MEXICO LOGO www.nckri.org

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NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6GEOPHYSICAL INVESTIGATION OF FLOOD-INDUCED SINKHOLE COLLAPSES, LAKEWOOD REGION, EDDY COUNTY, NEW MEXICOLewis Land Lasha Asanidze June 2014

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2 NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6Published and distributed byNational Cave and Karst Research InstituteDr. George Veni, Executive Director400-1 Cascades Avenue Carlsbad, NM 88220 USA www.nckri.org The citation information: Land L, Asanidze L 2014. Geophysical Investigation of Flood-Induced Si nkhole Collapses, Lakewood Region, Eddy C ountry, New Mexico. National Cave and Karst Resear ch Institute Report of Investig ation 6, Carlsbad, New Mexico. Cover photo: Lasha Asanidze examines a newly developing sinkhole next to Lakewood Road. Photo by George Veni. ISBN: 978-0-9910009-3-7NCKRI Organization and MissionNCKRI was created by the US Congress in 1998 in partnership with the State of New Mexi co and the City of Carlsbad. Initially an institute within the National Pa rk Service, NCKRI is now a non-profit 501(c)(3) co rporation that retains its federal, state, an d city partnerships. Federal and state funding for NCKRI is administered by the New Mexico Institute of Mining and Technology (aka New Mexico Tech or NMT). Funds not produced by agre ements through NMT are accepted directly by NCKRI. NCKRIs enabling legislation, the National Ca ve and Karst Research Institute Act of 1998, 16 USC. identifies NCKRIs mission as to: 1)further the science of speleology; 2)centralize and standardize speleological information; 3)foster interdisciplinary cooperation in cave and karst research programs; 4)promote public education; 5)promote national and international coopera tion in protecting the environment for th e benefit of cave and karst landforms; and 6)promote and develop environmentally sound a nd sustainable resource management practices.NCKRI Report of Investigation SeriesNCKRI uses this report series to publish th e findings of its research projects. The reports are produced on a schedule whose frequency is determined by the timing of the investigations. This series is not limite d to any topic or fi eld of research, exce pt that they involve caves and/or karst. To minimi ze environmental impact, few or no copies ar e printed. Electronic copies of this and previous reports are available for download at no cost from th e NCKRI website at www.nckri.org .

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NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6 3 TABLE OF CONTENTSExecutive Summary . . . . . . . .5 Introduction . . . . . . . . .6 Geologic Setting . . . . . . . .6 Methods . . . . . . . . .6 Results and Discussion . . . . . . .9Lakewood Road, East of Railroad . . . . . . .9 Lakewood Road, West of Railroad . . . . . . .10 Lake Road . . . . . . . . .11Conclusions . . . . . . . . 11 References . . . . . . . .13 Appendix . . . . . . . . .15LIST OF FIGURESFigure 1 Lakewood sinkhole locations . . . . . . . .7 Figure 2 Location of Lakewood electrical resistivity surveys. . . . . .8 Figure 3 Electrical resistivity profiles: Lakewood Road, north an d south shoulders, east of tracks. . .9 Figure 4 Electrical resistivity profiles: Lakewood Road, north and south shoulders, west of tracks .10 Figure 5 Electrical resistivity profiles: Lake Road, west and east shou lders. . . . .12

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NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6 5Executive SummaryBarnes1976Following flooding in September 2013, several areas near th e community of Lakewood in northern Eddy County, New Mexico, were damaged by multiple sinkhole collapses. Pettig rew & Associates contracted with the National Cave and Karst Research Institute (NCKRI) to conduct electrical resis tivity (ER) surveys for cavities to guide road repairs along Lake and Lakewood roads. ER surveys involve injecting an electrical current into the ground between two implanted metal electrodes and measuring the voltage drop between two additional electrodes. Given the current flow and voltage drop, the distribution of electrical resistivity in the subsur face can be measured and mapped ER surveys are one of the most effective methods for detecting airor water-filled caves. Interpretation of the resistivity data was informed by subsurface records from area water wells. Electrical resistivity surveys conducted parallel to Lakewood and Lake roads attained a maximum exploration depth of 55 to 62 m (180 to 203 ft .). Subsurface stratigraphy, in cluding clay-rich floodplain se diments, and mudstone and gypsum of the underlying Seven Rivers Formation can be iden tified by vertical and lateral variations in electrical resistivity. The irregular bedrock surface of the Seven Ri vers Formation reflects paleotopography developed on that surface prior to its burial by floodplain sediment. Some of the negative paleotopograp hic features are probably filled sinkholes that may be associated with shallowe r karstic features not imaged on the profiles. Two shallow high resistivity anomalies are visible on the Lake Road ER profile, and on the Lakewood Road profile east of the railroad tracks. These featur es most likely represent shallow subs urface cavities partia lly filled with unconsolidated sediment that are related to observed sinkholes and soil fractures. No near-surface resistivity anomalies along Lakewood Road we st of the railroad were observed, in spite of the presence of several shallow sinkholes along this section of the road. The small number of zones of probable subsidence found with the ER method in areas of known sinkhole collapse suggest that relatively narrow vertical channels are transmitting sediment into underlying cavities. The depth to bedrock indicated by the resistivity data demonstrates that remediation of the sinkholes is impr actical by conventional methods of excavation of bedrock followed by graded back-filling. Instead, dynamic compaction may be a more effective remediation technique, with added attention in areas where sinkh oles are known and the ER surveys suggest potential subsurface cavities.GEOPHYSICAL INVESTIGATION OF FLOOD-INDUCED SINKHOLE COLLAPES, LAKEWOOD REGION, EDDY COUNTY, NEW MEXICOLEWIS LANDNEW MEXICO BUREAU OF GEOLOGY AND MINERAL RESOURCESNATIONAL CAVE AND KARST RESEARCH INSTITUTEANDLASHA ASANIDZEVAKHUSHTI BAGRATIONI INSTITUTE OF GEOGRAPHYIVANE JAVAKHISHVILI TBILISI STATE UNIVERSITYTBILISI, GEORGIA

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6 NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6IntroductionFollowing flooding in September 2013, several areas along Lakewood Road and Lake Road in northern Eddy County, New Mexico, were damaged by multiple sinkhole collapses. Pettigrew & Associates contracted NCKRI to conduct electrical resistivity (ER) surveys for cavities to guide road repair s. NCKRI agreed to conduct this research to assist in solv ing a threat to public safety in addition to collecting additional geophysical data, to include in its database for future detailed studies of ER data collection methods and analyses. The sinkholes in the study area, cover collapse sinkholes, form by the piping of soil and alluvium into underlying karstic cavities. Their position along the two roads is the result of drainage channels along either side of each road, which have promoted groundwater recharge in these linear areas for many years. The piping of the unconsolidated materi als created cavities in the alluvium that slowly stoped up toward the surface and into the soil. The flood of September 2013 focused substantially greater flow down into the soil in the channels until the cavities became sufficiently large and unstable to collapse and breach the surface. A visual survey of the area by Pettigrew and NCKRI personnel on 12 February 2014 supported this hypothesis, finding that collapse and related feat ures appeared to diminish with distance from the roads ( Figure 1 ). Subsequent interviews with Lakewood residents revealed additional karstic fissures and sinkholes occurring several tens of meters from the roads, but still indicating the majority were concentrated along the drainage channels. For detailed discussion of sinkhole processes and remediation, see Sowers (1999) and Zhou and Beck (2011) Additionally, NCKRI manages the Multidisciplinary Conference on Sinkholes and the Engineering and Environmental Impacts of Karst. This conference series began in 1984, and its proceedings are highly sought internationally as the most comprehensive set of information on the topic. Most proceedings volumes are out of print but can often be found on-line through various book sellers. NCKRI has made the most current volume ( Land et al., 2013 ) digitally available via its website ( www.nckri.org ) as an open access publication.Geologic SettingEffective remediation of cover collapse sinkholes requires accurate characterization of piping zones and depth to bedrock. Stratigraphic units in the Lakewood area that are relevant to th is investigation include a surface layer of topsoil 0 to 5 m thick, which grades into underlying clay, sand, and gravel of the Pecos River floodplain. The thickness of floodplain deposits is highly variable because of paleotopographic relief developed on the underlying bedrock. Bedrock in the study area is represented by the Seven Rivers Formation, the middle unit of the Permian-age Artesia Group, which is composed of interbedded reddishbrown mudstone, siltstone, dolomite, and gypsum. The Seven Rivers Formation is exposed along the McMillan Escarpment on the eastern margin of the Pecos River valley, where it is capped by dolomites of the Azotea Tongue. Subsurface dissolution of gy psum within the Seven Rivers Formation and other members of the Artesia Group has caused local and re gional subsidence and has profoundly influenced topography along the margins of the Pecos River Valley. The presence of these highly soluble rocks has also contri buted to the formation of sinkholes and caves ( Land, 2003 ; Stafford et al., 2008). Lake McMillan, less than one kilometer east of Lakewood, was ultimately abandoned because of loss of water through karstic conduits within the underlying Seven Rivers Formation ( Cox, 1967 ). Based on a survey of well r ecords in the area, depth to the top of the Seven Rivers Formation in the vicinity of Lakewood ranges from 26 to 49 m. One well intersected a cave within the Seven Rivers Formation at a depth of aproximately 60 m.MethodsThe basic operating principle for electrical resistivity surveys involves generating a direct current between two metal electrodes implanted in the ground, while the ground voltage is measured between two additional implanted electrodes. Given the current flow and measured voltage drop between two electrodes, the subsurface resistivity betw een the electrodes can be determined and mapped. Resistivity profiles detect vertical and lateral variations in resistivity in the subsurface. Previous work has shown that resistivity surveys are among the most effective methods for identifying water-filled and especially air-filled voids due to their electrical cont rast with the surrounding bedrock.

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NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6 7Figure 1. Reconnaissance survey of sinkholes and subsidence fissures in Lakewood area.

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8 NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6Figure 2. Lakewood, NM, study area. ER survey lines parallel to Lake and Lakewood roads are indicated by red and blue dots; each dot represents one electrode in the array. Yellow filled circles show locations of sinkholes and other karst features photographed during resistivity surveys ( Appendix).

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NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6 9The depth of investigation fo r a typical ER survey is approximately one-fifth the length of the array of cable. NCKRI staff, assisted by personnel from Madron Services, conducted six electrical resistivity surveys parallel to Lake and Lakewood roads ( Figure 2), using 112 electrode arrays at an el ectrode spacing of 3 m, for a maximum deployment length of 333 m per array and an anticipated depth of investigation of approximately 65m. This spacing and target penetration depth were selected to determine if substantially larger cavities occur in the subsurface than are indicated by the size of the observed sinkholes, whic h should be considered in remediation of the sinkholes and repair of the roads. Four of the surveys employed a rollalong method to increase the length of the resistivity profiles. After data were collected for each 112 electrode array, the lower half of the array was shifted forward to the far end for a 50% overlap. Although this method does not increase the depth of investigation, it permits a seamless ER profile much longer than th e length of a single array. While resistivity data were collected, a survey-grade global positioning system (GPS) survey was conducted of all electrode positions fo r each array. The elevation data were used for advanced processing to correct for variations in topography along the survey line. We used SuperSting R8/IP electrical resistivity equipment provided by Advanced Geosciences, Inc. (AGI) to collect the resistivity data. The data were then processed using EarthImager 2D software. The EarthImager software chooses a resistivity scale designed to highlight natural conditions in the subsurface; thus resistivity pr ofiles shown in this report may not have the same resis tivity scale. AGI technical staff report that, in general, it is not advisable to force the software to adhere to a specific scale, and attempts to do so may yield misleading results.Results and DiscussionLakewood Road, East of Railroad Two rollalong resistivity surveys were conducted parallel to Lakewood Road, one on each shoulder, extending west from the intersection of Lake and Lakewood roads to the Burlington Northern and Santa Fe (BN&SF) railroad tracks ( Figure 2 ). These surveys achieved a maximum depth of investigation of 62 m below ground level. Variations in electrical resistivity are influenced by subsurf ace stratigraphy and facies variations ( Figure 3 ), and by the presence of subsurface cavities. Our interpretation of the resistivity data is informed by subsurface reco rds from area water wells, including an augmentation well drilled by the New Mexico Office of the State E ngineer (NM OSE) in 2006, located approximately 3.2 km southwest of the survey area. Three distinct stratigraphic uni ts can be identified on the resistivity profiles. A thin zone of relatively high resistivity occupies approximately the uppermost 5 m of the section and extends almost continuously across the profile from west to east. This high resistivity layer most Figure 3. Electrical resistivity profiles conducted along the no rth and south shoulders of Lake wood Road, east of the BN&SF railroad tracks.

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10 NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6likely represents air-filled porosity in unsaturated soil and gravel. Underlying this high resistivity layer is an interval approximately 30 to 50 m thick of generally lower resistivity (5 to 30 ohm-m). This layer probably represents a more clay-rich s ection of alluvial material of the Pecos River floodplain. Clays typically have lower resistivity than more coarse-grained sediments. A zone of moderately high resistivity extends across the profiles approximately 40 to 50 m below ground level. Based on well records in the survey area, we interpret this interval to represent mudstone and gypsum of the Seven Rivers Formation, which crops out along the McMillan Escarpment on the opposite side of the Pecos River. Undulations in the top of the Seven Rivers Formation reflect the paleotopography of the unit prior to burial by floodplain alluvium. A prominent depression in the top of the Seven Rivers is visible on the north shoulder profile be tween 138 and 165 m. This feature may represent a buried sinkhole filled with more electrically conductive clay, as indicated by a pod of very low resistivity material above it. A small, distinctive pod of relatively high resistivity occurs approximat ely 8 m below ground level at the west end of the south shoulder profile at 420 m, overlain by a near-surface interval of low-resistiv ity. A subdued reflection of this feature is also present on the north shoulder profile. Resistivity values are too low for this feature to be caused by an air-filled cave, but it may represent a shallow cavity f illed with unconsolidated sediment. Lakewood Road, West of Railraod Because of the presence of the railroad tracks, it was not possible to conduct continuous rollalong surveys on Lakewood Road. For this reason two separate surveys were conducted on the north and south shoulders on the west side of the railway ( Figure 4 ). These surveys achieved a maximum exploration depth of 60 m. A thin layer of high resistivity is also present on the profiles west of the railway, reflecting air-filled pore space in sand and gravel of the soil horizon. This layer is underlain by 40 to 50 m of generally lower resistivity material of the Pecos River floodplain. However, several lenticular bodies of higher resistivity are also present within this section. One distinctive highresistivity lens is present on the south shoulder profile between 110 and 140 m, approximately 15 m below ground level. A more laterally extensive high resistivity layer occurs beneath the west end of the north shoulder profile. Subdued reflections of both of these features are also present on the opposite shoulder profiles. Because of their geometry and their presence within the alluvial section, we interpret these fe atures as lenticular bodies of coarse sand and gravel in the unsaturated zone; it is unlikely that they represent caves. In spite of the presence of several small sinkholes along the shoulders of Lakewood Road west of the railway, no obvious subsurface cavities are visible on the ER profiles.Figure 4. Electrical resistivity profiles conducted along the north and south shoulder s of Lakewood Road, west of the BN&SF railroad tracks.

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NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6 11The top of the Seven Rivers Formation is poorly defined in the resistivity survey data collected west of the railway. It is possible that the top of the Seven Rivers exceeds our depth of investig ation in this area, dipping locally to the west. Although regional dip is to the east, the topography of the Pecos Valley has been strongly influenced by local and regional subsidence due to subsurface gypsum dissolution ( Bachman, 1984 ; Land, 2003 ), resulting in the presence of a number of sediment filled basins along the western margin of the river valley ( Lyford, 1973 ). Lake Road Two rollalong resistivity surveys were conducted along the west and east shoulders of Lake Road, extending north about one kilometer from the intersection of Lake and Lakewood roads. Both surveys attained a maximum depth of investigation of 55 m. The near-surface, high resis tivity soil horiz on is not as well defined on the Lake Road ER surveys. However, the lower resistivity, clay-ric h alluvial section is clearly visible, extending along the entire length of both profiles ( Figure 5). The Seven Rivers Formation is clearly defined by a high resistivity zone beneath the northern half of the profile approximately 25 m below ground level, and appears to be dipping gently to the south. The higher resistivity secti on that represents the Seven Rivers Formation is interrupted in several places, reflecting the paleotopography developed on the top of the formation. One of these breaks occurs on the west shoulder profile between 600 and 650 m, where a sag in the top of the unit most likely represents a filled sinkhole. Subsidence over this feature appears to have caused a local near-surf ace accumulation of coarser sediment, as indicated by an overlying lenticular high resistivity zone. This feature is also visible on the east shoulder profile between approximately 630 and 670 m. Several less defined breaks in the Seven Rivers profile may also represent filled sinkholes. A small but well defined pod of higher resistivity occurs at 305 m on the east shoulder profile, approximately 5 m below ground level. A second high resistivity pod occurs directly beneath the first at approximately 20 m below ground level. These features are likely to represent subsurface cavitie s partially filled with sediment, or two segments of a fissure adjacent to or extending beneath the roadway. A 4-m long soil fracture was identified near this section of the ER profile during the February, 2014, reconnaissance survey ( Figure 1 number 6).ConclusionsElectrical resistivity surveys conducted parallel to Lakewood and Lake roads near the community of Lakewood, NM, attained maximum exploration depths of 55 to 62 m. Subsurface stra tigraphy, including a nearsurface soil horizon, clay-ric h alluvium of the Pecos Valley floodplain, and mudstone and gypsum of the Seven Rivers Formation, are indicated by vertical and lateral variations in subsurf ace electrical resistivity. The irregular surface of the Seve n Rivers Formation on all profiles reflects paleotopography developed on that surface prior to its burial by floodplain alluvial sediment. Some of the negative paleotopographic features are almost certainly filled sinkholes, which may be associated with shallower karstic features not imaged on the profiles. Two distinct and well defined pods of high resistivity are visible on the Lake Road east shoulder profile and near the west end of the Lakewood Road south shoulder profile, just east of the BN &SF railroad tracks. These features most likely represent shallow subsurface cavities, partially filled with unconsolidated sediment, that are related to observed sinkholes and soil fractures. There were no observations of any near-surface resistivity anomalies indicativ e of karst features on the ER profiles west of the rail way, in spite of the presence of several shallow sinkholes along this section of Lakewood Road. However, the absence of a well defined Seven Rivers section on these profiles may be due to a broad zone of s ubsidence caused by subsurface dissolution of evaporites, also accompanied by a thicker accumulation of overlying floodplain alluvium. The few zones of probable subsidence found with the ER method in areas of known sinkhole collapse suggest the development of relatively narrow vertical piping channels to transmit sediment into underlying cavities. The clear imaging of the Seven Rivers Formation demonstrates that remediation of the sinkholes is impractical by the conventional method of excavation of bedrock followed by graded back-filling. Instead, it is recommended that dynamic compaction be considered as a remediation technique, with added attention in areas where sinkholes are known and the ER survey suggests potential subsurface cavities. Dynamic compaction has the potential to work especially well due to the clay-rich soil and alluvium present, but a geotechnical engineer experienced in sinkhole remediation should be consulted.

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12 NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6Figure 5. Electrical resistivity surveys conducted along the west and east shoulders of Lake Road.

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NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6 13ReferencesBachman1984Bachman G.O. 1984. Regional geology of Ochoan evaporites, northern part of Delaware Basin. New Mexico Bureau of Mines and Mineral Resources Circular 184.Cox1967Cox E.R. 1967. Geology and hydrology between Lake McMillan and Carlsbad Springs, Eddy Co., New Mexico. US Geological Survey Water Supply Paper 1828.Land2003Land L. 2003. Evaporite karst and regional ground water circulation in the lower Pecos Valley. In: Johnson KS, Neal JT, editors. Evap orite Karst and Engineering/ Environmental Problems in the United States. Oklahoma Geological Survey Circular 109. p. 2272.Land et al.2013Land L., Doctor D.H., Stephenson J.B. eds. 2013. National Cave and Karst Res earch Institute Symposium 2, Sinkholes and the Engineering and Environmental Impacts of Karst: Proceedings of the Thirteenth Multidisciplinary Conferen ce. Carlsbad, New Mexico.Lyford1973Lyford F.P. 1973. Valley fill in the Roswell-Artesia area, New Mexico. US Geological Survey Open File Report 73.Sowers1999Sowers G.F. 1999. Building on sinkholes: design and construction of foundations in karst terrain. ASCE Press, New York.Stafford et al.2008Stafford K., Land L., Klimchouk A. 2008. Hypogenic speleogenesis within Seven Rivers evaporites: Coffee Cave, Eddy County, New Mexico. Journal of Cave and Karst Studies 70: 47.Zhou and Beck2011Zhou W., Beck B.F. 2011. Engineering issues on karst. In: van Beynen PE, editor. Karst Management. Springer Science+Business Media, p. 9.

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NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6 15Appendix Sinkholes and other karst fe atures in the survey areaBelow are photographs and summary descriptions of sinkholes and other karst f eatures in the surv ey area. Figure numbers reference locations shown in Figure 2 UTM coordinates use WGS84 datu m, and are listed as easting, northing, and estimated precisi on. Fracture azimuths are given relative to true north.Figure A-1. Small collapse sinkhole, south side of Lakewood Road, filled with asphalt rubble; 0.46 m diameter. 559048, 3610704, 5 m.

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16 NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6Figure A-2. Soil fracture, north side of Lakewood Road. Length ~18 m, width 0.5 1.5 m, depth 0.5 1.0 m, azimuth 102. 559027, 3610715, 4 m.

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NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6 17Figure A-3. Soil fracture mostly filled with gravel, north side of Lakewood Road. Pavement damage suggests fracture most likely extends beneath road to opposite shoulder, where as phalt slabs may cover fracture extension. Length, ~18 m (assuming fracture extends beneath road), width 1.4 m, depth where not filled 0.6 m, azimuth 20. 559008, 3610714, 3 m.

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18 NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6Figure A-4. Small sinkhole, south side of Lakewood Ro ad. Diameter, 0.4 m, depth, 0.44 m. 558997, 3610704, 3 m.

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NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6 19Figure A-5. Soil fracture, south side of Lakewood Road, most ly filled with gravel. Pavement damage indicates fracture extends beneath road to opposite shoulder, where a recent pile of gravel probably buries north end of feature. Length >10 m (assuming fracture extends beneat h road), width 0.4 m, de pth where not filled, 0.4 m, azimuth 137. 558944, 3610701, 4 m.

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20 NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6Figure A-6a. First of a pair of sinkholes following a soil fr acture, south side Lakewood Road. Length 0.6 m, width 0.2 m, depth 0.9 m, fracture azimuth 62. 558449, 3610702, 2 m.

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NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6 21Figure A-6b. Second of a pair of sinkhol es following a soil fracture, south side La kewood Road. Length 0.83 m, width 0.41 m, depth 0.63 m, fracture azimuth 62. 558449, 3610702, 2 m.

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22 NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6. Figure A-7. First sinkhole in a cluster of five, north side Lakewood Road. First three sinkholes occur in a line oriented 122. Length 3.2 m, width 1.35 m, depth 2.3 m. 558430, 3610719, 3 m.

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NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6 23Figure A-8. Second sinkhole in a cluster of five, north side Lakewood Road. Length 1.58 m, width 1.0 m, depth 0.85 m. 558429, 3610721, 3 m.

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24 NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6Figure A-9. Third sinkhole in a cluster of five, north side Lakewood Road. Length 1.7 m, width 1.52 m, depth 0.9 m. 558427, 3610724, 3 m.

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NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6 25Figure A-10. Fourth sinkhole in a cluster of five, north side Lakewood Road. Length 3.6 m, width 1.92 m, depth 1.0 m. 558423, 3610719, 3 m.

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26 NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6Figure A-11. Fifth sinkhole in a cluster of five, north side Lakewo od Road. Length 0.84 m, width 0.38 m, depth 0.84 m. Sinkhole follows fracture with azimuth of 177. 558427, 3610725, 3 m.

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NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6 27Figure A-12a. Line of three sinkholes, north side Lakewood Road. Line of sinkholes is oriented azimuth 146. 558392, 3610717, 3 m.

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28 NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6Figure A-12b. First of three sinkholes in line, north side of Lakewood Road. Length 1.78 m, width 1.45 m, depth 0.87 m. 558392, 3610717, 3 m.

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NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6 29Figure A-12c. Second of three sinkholes in line, north side of Lakewood Road. Leng th 0.56 m, width 0.35 m, depth 0.69 m. 558392, 3610717, 3 m.

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30 NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6Figure A-12d. Third of three sinkholes in line, north side of Lakewood Road. Leng th 0.73 m, width 0.46 m, depth 0.57 m. 558392, 3610717, 3 m.

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NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6 31Figure A-13. Sinkhole, north side La kewood Road. Length 2.67 m, width 1.7 m, depth 0.64 m. 558385, 3610719, 3 m.

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32 NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6Figure A-14. Discontinuous soil fracture, mostly concealed by dense mesquite, west side of Lake Road. Length ~20 m, maximum width 1.55 m, maximum depth 1.37 m, azimuth 97. 559128, 3610938, 4 m.

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NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6 33Figure A-15a. First of two sinkholes following fracture, west sid e of Lake Road. Length 1.65 m, width 1.1 m, depth 0.7 1.6 m. Fracture azimuth 2. 559133, 3610963, 3 m.

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34 NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6Figure A-15b. Second of two sinkholes foll owing fracture, west side of Lake Road Length 1.62 m, width 0.54 m, depth 0.7 m. Fracture azimuth 2. 559133, 3610963, 3 m.

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NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6 35Figure A-16. Soil fracture, west side of Lake Road. Length 0.66 m, width 0.1 m, depth 0.4 m, azimuth 172. 559138, 3610973, 4 m.

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36 NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6Figure A-17. Soil fracture, west side of Lake Road. Length 2.0 m, width 0.19 m, depth 1.8 m, azimuth 172. 559137, 3610990, 4 m.

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NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6 37Figure A-18. Poorly exposed, irregular an d discontinuous soil fracture extending into mesquite. Length >20 m, width ~0.5 m, depth ~0.5 m. 559133, 3611008, 4 m.

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38 NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6Figure A-19. Soil fracture, west side of Lake Road. Pavement damage indicates that fracture extends beneath road to opposite shoulder, where a poorly exposed fracture with the same orie ntation extends into mesquite. Length ~15 m (assuming fracture extends beneath road), width ~0.5 m, maximum depth 1 m, azimuth 112. 559135, 3611177, 3 m.

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NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6 39Figure A-20. Sinkhole in asphalt, west shoulder of Lake Road Length 0.33 m, width 0.2 m, depth 0.3 m. This sinkhole aligns with asphalt patches in road that are probably filled sinkholes, and another sinkhole on th e opposite shoulder. Orientation of these features is azimuth 27. 559134, 3611322, 3 m.

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40 NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6Figure A-21. Sinkhole, east side of Lake Road. Length 0.3 m, width 0.23 m, depth 0.43 m. This sinkhole aligns with asphalt patches in road that are most likely filled sinkholes, and another sinkhole on the opposite shoulder. Orientation of these features is azimuth 27. 559144, 3611341, 3 m.

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NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6 41Figure A-22. Soil fracture extending into dense stand of mesqui te, west side of Lake Road. Length ~3 4 m, width 0.66 m, depth 0.4 m, azimuth 22. 559132, 3611532, 3 m.

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42 NATIONAL CAVE AND KARST RESEARCH INSTITUTE REPORT OF INVESTIGATION 6

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National Cave and Karst Research Institute400-1 Cascades Avenue Carlsbad, New Mexico 88220 USA 000937 7809919 ISBN 9780991000937 9


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