winter 2016
sinkholes: a hidden, real new mexico geohazard
The majority of New Mexicans probably underground water systems formed by the regard sinkholes as an exotic geohazard dissolution of soluble rock by circulating that occurs far away in other parts of groundwater. What does this mean? For the country. In places such as Florida or groundwater to circulate, it must be able Kentucky, sinkholes have opened beneath to move through the subsurface bedrock, and “swallowed” houses, roads, and primarily through cracks, called “joints.” classic Corvettes in the National Corvette In regions where bedrock is composed Museum (which occurred on February 12, of soluble rock types, such as limestone, 2014). However, New Mexicans living in dolomite, or gypsum, groundwater moving the east-central and southeastern parts of through joints actually dissolves the rock, the state may view sinkhole development creating cavities in the subsurface. as a real and present danger. Indeed, they The word karst is based on a 19th might be aware that Blue Hole, in the Century German modification of the Santa Rosa area, and most of the lakes Slavic word krs and the Italian carso, at Bottomless Lakes State Park east of which essentially both mean “a bleak, Roswell are, in fact, sinkholes (see photo waterless place.” Although this description on this page). Large cavities have been Mirror Lake, one of several sinkholes at Bottomless could apply to many desert landscapes, it Lakes State Park east of Roswell, where upward encountered when drilling water wells in artesian flow of groundwater through gypsum originally referred to a specific region—the this region, and oil and gas drillers have bedrock has produced solution-collapse sinkholes. barren, high plateau area of what was then discovered large voids in the subsurface. Photo by Lewis Land. northwest Yugoslavia (current-day Slovenia Residents in these regions may have also and Croatia). This area is characterized by state and U.S. highways, warning of the observed sudden muddying of regional well dry stream valleys, often ending abruptly, potential for a sinkhole encounter (see waters after major rainfall events, as well as and numerous depressions. Water, instead second photo on page two). standing water collecting in low-lying areas of running freely over the land, seemingly Sinkholes associated with oilfield activities in pastures and fields. The phenomena of sinks into the ground. differ from the numerous others throughout sinkholes, subsurface cavities, intercon- All rocks, given sufficient time, undergo the region in that they are man-made, or nectivity of water-bearing strata directly physical weathering, which results from the anthropogenic. We now know, largely affected by large weather systems, and disintegrative erosional processes caused through geophysical work carried out by the slow, barely noticeable subsidence by flowing water and wind, and chemical the National Cave and Karst Research of depressions in the land surface are all weathering, which results when rocks and Institute (NCKRI) with the New Mexico related; they occur in areas characterized by minerals are dissolved into constituent Bureau of Geology and Mineral Resources soluble bedrock and are all part of so-called molecules that can be washed away from (NMBGMR), that another potentially cata- karst landscapes. More than 25 percent of the rock mass. In the case of carbonate strophic anthropogenic sinkhole could form the world’s population either lives on karst and evaporitic rocks, water and carbonic on the south side of Carlsbad, beneath the terrain or derives its water from karstic acid act as the chemical weathering agents intersection of U.S. Highway 285 with U.S. aquifers. In 2008, two very large sinkholes that break these rocks down. Carbonic Highway 62, an interchange known locally (approximately 111 m [364 ft] and 64 acid forms when meteoric water (rain) as the South Y. This hazard is discussed later m [210 ft]) in diameter, respectively, combines with carbon dioxide, which is in this article. abruptly formed in the oil fields east of produced by organic constituents in the the Pecos Valley and made national news. Karst, hydrology, and solution soil. Similar dissolution can take place on See photo on page two. If southeastern processes your teeth, through exposure to carbonic New Mexicans were previously unaware of acid in soft drinks, and can cause cavities. The term karst describes a landscape this hidden geohazard, they were alerted Most karst features in the eastern United containing caves, sinkholes, and extensive by news reports and hazard signs on both States and other karst areas around the
Published by the New Mexico Bureau of Geology and Mineral Resources • A Division of New Mexico Tech JWS Sinkhole: Karst features and landforms 07-28-2008: 10:00 am Limestones and dolomites, wherever 111 m (364 ft) diam exposed at the surface, will, over time, show numerous minor solution effects. These small (one to several centimeters in size) etched pits, grooves or runnels, hollows or flutes, are often separated by small, knife-like ridges and pinnacles. Collectively, these features are known by the German term, karren. Dissolution may 111 m be concentrated along joints in the bed- rock, and widening of these joints forms large conduits, enhancing the infiltration and circulation of water through the rocks. While karren terrain might be painful to bare feet and hard on shoes, it is relatively harmless compared to the hazards wrought by the sudden formation of large-scale karst 108.65 m features. Subsurface karstic cavities enlarge and coalesce, forming underground chan- nels for groundwater flow, ultimately allow-
0 50 m ing collapse of the overlying land surface. Of County Rd-217 the resulting karst landforms, such as closed depressions and sinkholes, are the most The JWS Sinkhole, one of two anthropogenic sinkholes that opened above brine extraction wells common, often occurring by the thousands in 2008 in the Loco Hills area of northern Eddy County. Courtesy of National Cave and Karst Research in major karst areas. Disappearing streams, Institute. large springs, and cave systems also typify world are formed in the carbonate rocks, These evaporitic rocks are much more karst terrain. limestone (calcium carbonate) and/or dolo- soluble than carbonates in the presence of Streams “disappear” when surface water mite (calcium-magnesium carbonate). In fresh water, and do not require carbonic flows or infiltrates into underground cavi- arid and semi-arid areas such as southeast- acid for dissolution to occur. ties. This process creates landforms such ern New Mexico, however, as blind valleys (where a valley terminates karst features more com- against a rock wall and the stream abruptly monly form in evaporitic disappears), pocket valleys (essentially the bedrock. Evaporites are a opposite, where groundwater discharges type of rock produced by from a spring and flows down a valley), salts left behind during the and dry valleys (occupied by no surface evaporation of saline water. stream, but often above a subsurface one). The most common types of During a storm event, surface runoff in dry evaporite rock are gypsum, valleys infiltrates rapidly into subsurface composed of calcium sul- conduits (see photo on page three). fate, and halite, the mineral name for sodium chloride, Disappearing reservoirs or table salt. Thick deposits Somewhat similar to disappearing of gypsum and halite are Highway sign adjacent to NM State Highway 360, east of streams, two New Mexico reservoirs, the present at the surface and in Hondo Reservoir and Lake McMillan, the subsurface throughout Artesia, warning of the possible sinkhole/subsidence hazard. Photo by Lewis Land. “disappeared” during the 20th Century the Permian Basin region of and ultimately had to be abandoned. southeastern New Mexico and west Texas. In some geologic settings, karstic cavities Problems began for the Hondo Project From roughly the vicinity of Carlsbad may also form by dissolution related to even before the reservoir was built to store northward, evaporite rocks were formed hydrogen sulfide. This gas rises up from water for irrigation. In 1904, the director in mudflats of vast, shallow lagoons, deep reservoirs of hydrocarbons. When of the newly created U.S. Reclamation between 270–250 million years ago. As mixed with groundwater, sulfuric acid Service was shocked to discover that large the sea retreated, the water evaporated, is formed. This acid attacks carbonates cavities occupied the floor of the proposed resulting in precipitation of the salts. With much more vigorously than meteoric reservoir site, located about 18 km (11 mi) time, these calcium-, magnesium-, and water or carbonic acid. Carlsbad Caverns, southwest of Roswell. Nevertheless, offi- sodium-enriched deposits were lithified Lechuguilla Cave, and other cave systems cials were mollified by proponents’ claims into gypsum and anhydrite (hydrated and in the Guadalupe Mountains of southeast that there were more than sufficient quan- anhydrous calcium sulfate, respectively), New Mexico and west Texas have formed tities of local clay for sealing the floor. The halite, and other more exotic minerals. through this dissolution process. reservoir was completed in 1907 but was new mexico earth matters 2 winter 2016 never able to hold significant quantities of in the world at that time. Nevertheless, water. In several of the post-construction because of the gypsum bedrock beneath the years, attempts were made to repair the lakebed, and adjacent gypsum bluffs of the lakebed, but larger holes kept being dis- McMillan Escarpment east of the valley, covered, and the repairing of the reservoir the reservoir almost immediately began floor was finally abandoned. Around leaking, particularly along the eastern 1917, the Reclamation Service gave up on margin of the lake. Much of the reservoir the project entirely. water, lost through karstic conduits, Lake McMillan Reservoir, which resurfaced in a series of springs in the Pecos stored Pecos River water for the Carlsbad River appproximately 6 km (3.5 mi) down- Irrigation District, also leaked for much stream. A seepage-control and containment of its 98-year history and was eventually levee was constructed in 1908–09 to replaced by Brantley Reservoir, located prevent the water from reaching the bluffs, 10 km (6 mi) downstream. Lake McMillan but during high water levels and occasional Dam, completed in 1893, the first large- breaks in the levee, whirlpools could be scale irrigation project on the Pecos River, seen on the lake, and high rates of leakage was designed with a storage capacity of occurred. In 1991 McMillan Dam was This tributary of Chalk Bluff Draw, southeast 138,000 acre-feet. Improvements made breached and Lake McMillan was allowed of Artesia, is a typical karst dry valley. Surface on the dam in 1894 and 1904 following to drain into Brantley Lake. Based on runoff, quickly infiltrates into the ground via damaging floods made it the largest dam recommendations by the U.S. Geological the two small sinkholes that developed in the channel floor.Photo by David J. McCraw. Solution sinkhole Buried sinkhole Survey, the new reservoir is located mostly A B Possible compaction depression on carbonate bedrock, which is less prone to sinkhole formation than the gypsum ure enlarge Fiss ment bedrock underlying former Lake McMillan. urface corr S osion Minor collapse Soil Sinkhole formation and the human impact Sinkholes are a diagnostic karst landform. Limestone Limestone Sinkholes are typically circular to elliptical in shape, and wider than they are deep. Caves and fissures Shapes vary considerably, ranging from a disc or shallow bowl to the much more Collapse sinkhole Caprock sinkhole common funnel form to even a vertical C Fallen blocks D cylinder. Although numerous mechanisms are responsible for the creation of sink- Stoping collapse holes, they can be generalized into three categories: 1) Those formed by surface or
Caprock near-surface bedrock dissolution (panels A and B) on left; 2) Those formed by collapse of bedrock overlying cavities (panels C and D); and 3) Those formed entirely in Cave Cave the soil overlying solutional cavities in the Cave Limestone Limestone bedrock (panels E and F). Cave Solution sinkholes and buried sinkholes Subsidence sinkhole – dropout Subsidence sinkhole – suffosion (A and B) are widespread around the E F Soil washing world, but they form relatively slowly, into fissure resulting in minimal human impact. Collapsed soil Like all solutional landforms, these are dependent on the following factors: topography and slope, the type of bedrock and its degree of jointing, and the amount of vegetation and soil cover. Typically, for Cohesive soil Non-cohesive solution-sinkhole formation and growth soil to occur, three conditions are met: 1)
Limestone Limestone Location in swales on otherwise flat terrain where ponding accelerates infiltration; 2) Fissure or cave Fissure or or Cave cave Presence of well-jointed bedrock beneath the swale, which favors zones of cavity- Mechanisms of sinkhole formation. Modified from Waltham, 2008, Quarterly Journal of Engineering Geology and Hydrogeology, v.41, p. 292. causing, preferential fluid flow, as opposed new mexico earth matters 3 winter 2016 to areas of diffuse infiltration; 3) Presence TA126 (13.9 km) of good vegetation and soil cover, which 10
provides an ample CO2 source to form acidic waters for dissolution. 5 Bedrock-collapse sinkholes (panels C
and D) are fairly rare and therefore have 0 little societal impact. Like cave formation, these features take several thousands -5 of years or more to develop before the
subsurface cavities grow to sufficient size (microns/s) Ground Velocity 7-16-08 -10 that weight of the overlying bedrock can 7-14-08 7-15-08 7-16-08 08:15 am 7-17-08 no longer be supported. 00:00:00 00:00:00 00:00:00 00:00:00 The most common type of sinkholes, and A July 2008 three-day seismograph record of vertical ground velocity measured by seismometer also those that represent the most serious TA126, located approximately 13 km (8 mi) from the JWS brine well, showing more than geohazard, form either by collapse or by six hours of ground motion leading up to sinkhole formation. The estimated time of surface subsidence of the soil or surficial sediments breaching (8:15 am) is depicted by a vertical red line. By Lewis Land. (cover or overburden) (panels E and F). the weight of the surficial sediments, in Winkler County, Texas, the Borger Cover-collapse sinkholes, or dropout pavement, etc. can no longer be sup- sinkholes in Hutchinson County, Texas, sinkholes, form by the abrupt collapse of ported, and dropout collapse occurs. This the Jal sinkhole in Lea County, New compacted, often clay-rich sediments over process results in pseudokarst, and it can Mexico, and the 2008 Loco Hills and JWS a cavity. Cover-subsidence sinkholes, on occasionally be catastrophic. In a suburb sinkholes in northern Eddy County, New the other hand, form by suffosion, a process of Guatemala City in 2007, a major sewer Mexico. Fortuitously, four months prior wherein loose soil and sediments wash failure following a period of heavy rains to formation of the JWS sinkhole, a seis- downward into open fissures and cavities triggered a dropout of more than 20 m mometer had been installed as part of the within the top of the underlying bedrock. (66 ft) across in the middle of the night, National Science Foundation’s EarthScope Like the buried sinkhole example shown swallowing five houses and a road and USArray program approximately 13 km in panel B, depression of soil can be a slow killing three people. (8 mi) to the southeast. About six hours process. However, most sinkholes of this prior to the collapse, the instrument type experience a sudden initial drop, fol- Other anthropogenic sinkholes (TA126) began recording high frequency lowed by additional slow subsidence. and the Carlsbad “South Y” seismic signals, presumably produced by Pseudokarst In the evaporitic rocks of southeastern the collapse of large blocks off the brine New Mexico and west Texas, improperly cavern’s roof. These signals continued until City streets occasionally collapse due to a cased abandoned oil wells, as well as solu- the collapse occurred at 8:15 am on July burst, buried water main. Although the tion mining practices used to obtain brine 16th (above). Less than four months later, news media call these collapses “sinkholes,” from near-surface salt beds, have created another brine-well collapse occurred in they do not meet the defining criteria, as subsurface voids directly responsible for northern Eddy County within the small they do not form by dissolution. During catastrophic collapse-sinkhole formation. community of Loco Hills. collapses caused by water main failure, During solution-mining operations, fresh Following the collapse of the Loco suffosion is the initial culprit. After water is pumped into the salt bedrock, Hills sinkhole, the New Mexico Oil pipe failure, high-pressured water starts circulated until it reaches saturation, and Conservation Division (NMOCD) immediately washing away the finest the resultant brine is pumped out. The imposed a six-month moratorium on all grained sediment. As small voids develop brine from extraction wells is used during brine well operations and began a review of the remaining sediment begins to flow into construction of oil and gas wells to enhance other brine wells in the state. In the review, these new voids and is also washed away, production. Examples of solution-mining it was determined that the I&W brine well allowing void spaces to grow. Eventually induced sinkholes include the Wink sinks on the south (continued on last page) S N wellhead US285 6 72 138 204 270 336 399 465 561 627 m Ohm-m 953 50,000
896 3,344 D C A B 839 Rustler 224
782 Salado 15.0 Elevation (m) Castile 724 1.0 Iteration = 8; RMS error -25.94%; Electrode spacing = 6 m
Profile of ER array line INW4 showing four distinct cavities in blue (A–D); black dots show individual electrode locations. The names Rustler, Salado, and Castile indicate the geologic formations represented in the cross section. By Lewis Land. new mexico earth matters 4 winter 2016 bureau news
Although most of the examples within the book are from the United States and Puerto Rico (New Mexico samples, like the cover art, are common throughout the book), there are also photographs of samples from 32 other countries.
Photo courtesy of Peter Mozley. Volume 16, Number 1 AAPG award for Scholle book Published twice annually by the New Mexico Bureau of Geology Drs. Dana Ulmer-Scholle (Research and Mineral Resources Professor at NM Tech) and Peter Scholle Matthew J. Rhoades, CPG, RG (Emeritus Director of the Bureau of State Geologist and Director Photo courtesy of Martha Cather. Geology and Mineral Resources) were a division of the lead authors on a recently completed Demolition of old Bureau of New Mexico Institute of Mining and Technology book—A Color Guide to the Petrography Geology building of Sandstones, Siltstones, Shales, and Daniel H. López While machinery knocked down the old President Associated Rocks. Published by the bureau building in December, there was 801 Leroy Place American Association of Petroleum Socorro, New Mexico 87801-4750 Geologists (AAPG) as Memoir 109, the much discussion of the 45-year history that (575) 835-5420 540-page, full-color, hardbound book is building represented. Since its inception in 1927, the bureau has been located in Bureau Albuquerque office designed to help students, instructors and 2808 Central SE industry professionals with the microscopic 4 different buildings on campus. First, Albuquerque, New Mexico 87106 study of siliciclastic rocks and associated the basement of Brown Hall until 1949, (505) 366-2530 second, in old Workman Center, and third, deposits (cherts, evaporites, and others). It Visit our website at: contains over 1,100 light microscope and the Workman Annex built during the mid geoinfo.nmt.edu scanning electron microscope images of 1970s. The bureau is now located in the grains, textures, and structures of clastic much-celebrated Headen Center. For more Board of Regents Ex Officio terrigenous rocks as well as their diagenetic information about the bureau’s history Susana Martinez alteration (compaction, cementation, go to: geoinfo.nmt.edu/publications/ Governor of New Mexico dissolution, and replacement) and porosity periodicals/earthmatters/5/n2/em_v5_ Dr. Barbara Damron reduction or enhancement. In addition, n2.pdf Secretary of Higher Education full-color diagrams, an extensive glossary, Appointed index, foldout birefringence chart, and Deborah Peacock an included DVD with Powerpoint files President, 2011–2016, Corrales of all of the petrographic images provide Jerry A. Armijo additional information for both novices Secretary/Treasurer, 2015–2020, Socorro and experienced practitioners. David Gonzales
The volume also provides classification 2015–2020, Farmington Donald Monette diagrams for accurate description of sedi- 2015–2018, Socorro mentary rocks and their porosities. Perhaps Myissa Weiss, student member most importantly, the book, through its View new video about the Bureau 2015–2016, Farmington extensive picture captions, emphasizes of Geology Editors paragenesis, the sequencing of events in Nelia Dunbar the post-deposition history of sedimentary This short informational video, produced Gina D’Ambrosio rocks. The ability to distinguish the relative by the staff of the New Mexico Bureau of Richard Arthur timing of compaction, dissolution, cemen- Geology and Mineral Resources, explains Layout & Graphics tation, and deformation events is critically who we are and what we do for the State of Gina D’Ambrosio important in petroleum and minerals New Mexico. In addition to highlighting Leo Gabaldon exploration (and in general geologic inves- our research and service missions, the video Earth Matters is a free publication. tigations as well), and petrography is argu- also showcases our new building, which For subscription information please call ably the most important tool to accomplish was completed in April 2015. View the (575) 835-5490, or e-mail us at [email protected] such studies, especially when used in video at: geoinfo.nmt.edu/about/video/ conjunction with a variety of radiometric home.html Cover photo of Chimney Rock, New Mexico dating and thermal history analysis tools. © Matthew Zimmerer new mexico earth matters 5 winter 2016 New Mexico Bureau of Geology & Mineral Resources NONPROFIT ORGANIZATION New Mexico Institute of Mining & Technology U.S. Postage 801 Leroy Place PAID Socorro, New Mexico 87801-4750 Return service requested permit no. 1888 Albuquerque, NM
sinkholes: a hidden, real new mexico geohazard (continued)
side of Carlsbad was in a similar geologic voltage drop between electrodes, with state-of-the-art scientific data and inter- setting to the JWS and Loco Hills differences in subsurface electrical pretation to make informed environmental sinkholes and had a similar drilling history, resistivity can be determined, and profiles and emergency management decisions continuously pumping brine since 1979. illustrating vertical and lateral variations regarding the potential hazards of living in a Because the I&W operation was located in subsurface resistivity are generated. karst-prone region. near the intersection of two major U.S. Subsurface voids filled with brine are easy —David J. McCraw and Lewis Land highways known locally as the “South Y,” to detect because of the very low resistivity the BNSF rail line, the Carlsbad Irrigation of saline water. District’s South Canal, a feed store, a The South Y ER survey consisted of six mobile home park, a truck stop, and a array lines of 112 electrodes each, spaced David J. McCraw has worked for 20 years church, NMOCD permanently closed six meters apart. As seen on the accom- at the bureau concentrating on geologic the brine well operation and fined I&W, panying plot of line INW4 (on page 4), mapping, geologic map making, and earth which then declared bankruptcy. The City four distinct blue polygons (labeled A-D) surface processes. of Carlsbad and Eddy County established representing subsurface voids, can clearly Lewis Land is a karst hydrogeologist with a Brine Well Working Group, and with be seen. These four cavities were created the bureau and is the bureau’s liason with NMOCD research funds set up a monitor- by the two I&W injection/extraction the National Cave and Karst Research ing array of tilt-meters to warn of potential wells. Sinkhole hazard warning signs are Institute in Carlsbad, New Mexico. collapse and established emergency man- now posted on all roads leading into the agement protocols. Attempts were made South Y interchange; the area is now to measure the size and shape of the cavity continuously monitored using surface using sonar methods, but these attempts and downhole tilt-meters; and remedia- were unsuccessful. NCKRI, in conjunction tion plans are under consideration by with NMBGMR personnel, was then NMOCD and the city of Carlsbad. For more information about the funded to conduct an electrical resistivity Depressions form and enlarge, and bureau and its publications: (ER) survey in 2011 to measure the cavity’s new sinkholes form almost on an annual approximate size and shape. basis in southeastern New Mexico. The Visit our website at http://geoinfo.nmt. During an ER survey, evenly spaced NMBGMR continues to focus on geologic edu; Call (575) 835-5490, or e-mail us at electrodes are driven into the ground in a mapping and research as well as hydrogeo- [email protected]; or visit our linear array and a direct electrical current logic assessments, aquifer characterization, Publications Office at our new location is generated between a pair of electrodes, and groundwater monitoring in this region. on the corner of Bullock and Leroy on the while an adjacent pair is used to record the We are also involved in public outreach and campus of New Mexico Tech, 801 Leroy ground voltage. Given the current flow and education, and provide decision makers Place, Socorro, NM, 87801. new mexico earth matters winter 2016