GROUND-WATER RESOURCES FOR THE FUTURE Land Subsidence in the United States

Mining Ground Water Ground water is among the Nation’s most important natural resources. It provides drinking water to urban and rural communities, supports irrigation The compaction of unconsolidated aqui- and industry, sustains the ow of streams and rivers, and maintains riparian fer systems that can accompany excessive and wetland ecosystems. In many areas of the Nation, the future sustain- ground-water pumping is by far the single ability of ground-water resources is at risk from overuse and contamination. largest cause of subsidence. The overdraft Because ground-water systems typically respond slowly to human actions, of such aquifer systems has resulted in a long-term perspective is needed to manage this valuable resource. This permanent subsidence and related ground failures. In aquifer systems that include publication is one in a series of fact sheets that describe ground-water- semiconsolidated silt and clay layers (aqui- resource issues across the United States, as well as some of the activities of tards) of sufcient aggregate thickness, the U.S. Geological Survey that provide information to help others develop, long-term ground-water-level declines can manage, and protect ground-water resources in a sustainable manner. result in a vast one-time release of “water of compaction” from compacting aquitards, which manifests itself as land subsidence recent U.S. Geological Survey Subsidence is a global problem and, in (g. 2). Accompanying this release of water (USGS) report (Galloway and the United States, more than 17,000 square is a largely nonrecoverable reduction in the others, 1999) shows that sustain- miles in 45 States, an area roughly the A pore volume of the compacted aquitards, able development of our land and water size of New Hampshire and Vermont com- and thus a reduction in the total storage resources depends on improved scientic bined, have been directly affected by subsid- capacity of the aquifer system. This “water understanding and ence. The principal detection of sub- causes are aquifer- sidence. The report system compaction, features nine illus- drainage of organic trative case studies soils, underground that demonstrate mining, hydrocom- the role of subsur- paction, natural com- face water in hu- paction, sinkholes, man-induced land and thawing per- subsidence (http:// mafrost (National water.usgs.gov/ Research Council, pubs/circ/circ1182). 1991). Three dis- More than 80 per- tinct processes cent of the identi- Figure 1. Development of a new irrigation well in account for most ed subsidence in west-central Florida triggered hundreds of sinkholes of the water-related over a 20-acre area. The sinkholes ranged the United States in size from less than 1 foot to more than 150 feet subsidence—com- is a consequence in diameter. paction of aquifer of human impact systems, drainage on subsurface water, and is an often over- and subsequent oxidation of organic soils, looked environmental consequence of our and dissolution and collapse of suscep- land and water-use practices. The increas- tible rocks. ing development of our land and water resources threatens to exacerbate exist- Figure 2. Approximate location of maximum ing land-subsidence problems and initi- subsidence in the United States identified by ate new ones (g.1). research efforts of Dr. Joseph F. Poland (pic- tured). Signs on pole show approximate altitude Land subsidence is a gradual settling or of land surface in 1925, 1955, and 1977. The sudden sinking of the Earth’s surface owing site is in the San Joaquin Valley southwest of to subsurface movement of earth materials. Mendota, California.

U.S. Department of the Interior USGS Fact Sheet-165-00 U.S. Geological Survey December 2000 Nevada Idaho Colorado New Jersey Las Vegas Valley Raft River area Denver area Atlantic City-Oceanside area Barnegat Bay-New York Bay coastal area

Figure 3. Some of the areas where subsid- ence has been attributed to the compaction Delaware of aquifer systems caused by ground-water California Bowers area pumpage. Antelope Valley Dover area Coachella Valley Elsinore Valley La Verne area Lucerne Valley Mojave River Basin Virginia Oxnard Plain Franklin-Suffolk area Pomona Basin Williamsburg-West Point area Sacramento Valley Salinas Valley San Benito Valley New Mexico Louisiana Major unconsolidated aquifer systems San Bernardino area Albuquerque Basin Baton Rouge area San Gabriel Valley Mimbres Basin New Orleans area in the conterminous United States San Jacinto Basin Georgia (modified from Clawges and Price, 1999) San Joaquin Valley Arizona Texas Savannah area San Luis Obispo area Avra Valley Houston-Galveston Santa Clara Valley East Salt River Valley Hueco Bolson-El Paso, Juarez Temecula Valley Eloy Basin Wolf Valley Gila Bend area Harquahala Plain San Simon Valley Stanfield Basin Tucson Basin West Salt River Valley Willcox Basin of compaction” cannot be reinstated by to subsidence that has permanently allowing water levels to recover to their increased ood risks in the greater San predevelopment status. The extraction of Jose area. In nearby San Joaquin Val- this resource for economic gain consti- ley, one of the single largest human tutes “ground-water mining” in the truest alterations of the Earth’s surface topog- sense of the term. raphy has resulted from excessive ground- Five case studies demonstrate how water pumpage to sustain an exceptionally agricultural and municipal-industrial productive agriculture (g. 2). The banner ground-water use have depleted critical photo (front page, top) shows the Cal- ground-water resources and created ifornia Aqueduct coarsing through the costly regional-scale subsidence (g. 3). San Joaquin Valley. The aqueduct conveys Figure 4. Homes at Greens Bayou near Hous- ton, Texas, where 5 to 7 feet of subsidence These include the Santa Clara Valley water from the Sacramento-San Joaquin Delta to basins affected by subsidence in has occurred, were flooded during a storm in in northern California, where early agri- June 1989. cultural ground-water use contributed central and southern California. Early oil and gas production and a long history of ground-water pumpage in the Hous- pumpage, thereby halting or slowing sub- ton-Galveston area, Texas, have created sidence, at least temporarily. severe and costly coastal-ooding haz- ards and affected a critical environmen- Drainage of Organic Soils tal resource—the Galveston Bay estuary Land subsidence invariably occurs (g. 4). In Las Vegas Valley, Nevada, when soils rich in organic carbon are ground-water depletion and associated drained for agriculture or other purposes. subsidence have accompanied the con- The most important cause of this subsid- version of a desert oasis into a thirsty ence is microbial decomposition, which, and fast-growing metropolis. Water- under drained conditions, readily converts intensive agricultural practices in south- organic carbon to carbon-dioxide gas and central Arizona caused wide-spread water. Compaction, desiccation, erosion by subsidence and ssuring of the Earth’s wind and water, and prescribed or acciden- surface (g. 5). In each of these areas, tal burning can also be signicant factors. however, importation of surface water The total area of organic soils in the has reduced or stabilized ground-water United States is roughly equivalent to the size of Minnesota, about 80,000 square Figure 5. Some of the most spectacular miles, nearly half of which is “moss peat” examples of subsidence-related earth fissures located in Alaska (Lucas, 1982) (g. 6). occur in south-central Arizona. About 70 percent of the organic-soil area many areas they are buried at great depths (Martinez and others, 1998). Natural solution-related subsidence has occurred in each of the major salt basins in the United States (Ege, 1984). The high solu- Figure 6. Most organic bilities of salt and gypsum permit cavities soils occur in the north- ern contiguous 48 States to form in days to years, whereas cavity and Alaska. formation in carbonate bedrock is a very slow process that generally occurs over centuries to millennia. Human activities can expedite cavity formation in these susceptible materials and trigger their collapse, as well as the collapse of pre- existing subsurface cavities. Though the collapse features tend to be highly local- ized, their impacts can extend beyond the collapse zone via the potential introduction of contaminants to the ground-water system. in the contiguous 48 states occurs in Delta of California and the Florida Two cavity-collapse case studies—Retsof, northerly, formerly glaciated areas, where Everglades—continuing organic-soil New York, and west-central Florida— moss peats are also common (Stephens subsidence threatens agricultural pro- document human-induced cavity collapses and others, 1984). Moss peat is composed duction, affects engineering infrastruc- in salt and limestone, respectively. mainly of sphagnum moss and associated ture that transfers water supplies to species. It is generally very acidic (pH 3.5 large urban populations, and complicates to 4) and, therefore, not readily decom- ongoing ecosystem-restoration efforts posed, even when drained. However, sponsored by the Federal and State gov- where moss peat is amended for agricul- ernments. Subsidence-weakened levees tural cultivation, for example through fer- increase the potential for ooding of tilization and heavy application of lime to Delta islands, which could in turn disrupt raise the pH, it can decompose nearly as freshwater ows and threaten the integ- rapidly as other types of organic soils. rity of the vast north-to-south water- transfer system in California. In the Two case studies of organic-soil sub- Everglades agricultural area, where the sidence focus on examples of rapid sub- value of all agricultural crops is currently sidence (1 to 3 inches/year) caused by about $750 million (Snyder and Davidson, decomposition of the remains of shal- 1994), agriculture as currently practiced low-water sedges and reeds. In two has a nite life expectancy because of the of the Nation’s important wetland eco- ongoing subsidence (g. 7). systems—the Sacramento-San Joaquin Collapsing Cavities The sudden and sometimes catastrophic Figure 8. Collapse sinkholes, such as this one in Winter Park, Florida (1981), may develop subsidence associated with localized collapse abruptly (over a period of hours) and cause of subsurface cavities (sinkholes) (g. 8) is catastrophic damage. detailed in two case studies. This type of sub- sidence is commonly triggered by ground- water-level declines caused by pumping and The Role of Science by enhanced percolation of ground water. The occurrence of land subsidence is Collapse features tend to be associated seldom as obvious as it is in the case of cata- with specic rock types, such as evaporites strophic sinkholes or mine collapses. Where (salt, gypsum, and anhydrite) and carbon- ground-water mining or drainage of organic ates (limestone and dolomite) (g. 9). These soils are involved, the subsidence is typi- rocks are susceptible to dissolution in water cally gradual and widespread, and its dis- and the formation of cavities Salt and gyp- covery becomes an exercise in detection. sum are much more soluble than limestone, Gazing out over the San Joaquin Valley, the rock type most often associated with California today, one would be hard-pressed Figure 7. This building at the Everglades Experi- catastrophic sinkhole formation. ment Station was originally constructed at the to recognize that fewer than 75 years ago land surface; latticework and stairs were added Evaporite rocks underlie about 35 to the land surface was nearly 30 feet higher after substantial land subsidence. 40 percent of the United States, though in in some locations (g. 2). Subsidence detec- Figure 9. Salt and gypsum underlie about 40 percent of the contiguous United States. Carbonate karst land- scapes constitute about 40 percent of the United States east of Tulsa, Okla- homa (White and others, 1995).

Tulsa Evaporite rocks—salt and gypsum Karst from evaporite rock Karst from carbonate rock (modified from Davies and Legrand, 1972) tion and mapping programs are critical to Land surveys establish bench-mark posi- have been established, subsidence can the scientic understanding and manage- tions to accurately locate roadways, ood be mapped. This has traditionally been ment of our land and water resources. and drainage-control structures, pipe- accomplished using spirit leveling and, The detection of regional-scale subsid- lines, and other engineered infrastructure. more recently, Global Positioning System ence has historically depended on the dis- Once unstable bench marks are dis- (GPS) surveys. A new tool has emerged covery that key bench marks have moved. covered, and truly stable bench marks in the past decade that has dramatically improved our capability to detect and map land-surface deformation. This tool, Figure 10. This InSAR-derived surface-defor- 95 interferometric synthetic aperture radar mation map shows subsidence in the Las Vegas Valley between April 1992 and December 1997 Eglington (InSAR), uses repeat-pass radar images (Amelung and others, 1999). The subsidence fault from Earth-orbiting satellites to measure is caused by aquifer-system compaction and subsidence and uplift at unprecedented controlled in part by surface faults, which have levels of spatial detail (80 m x 80 m) and also been the focal point of earth-fissure for- L 15 mation. a measurement resolution (sub-centimeter) s (Galloway and others, 2000) (g. 10). Once subsidence is identied and V mapped, subsidence-monitoring programs e can be implemented and scientic studies g a Las Vegas can be launched to improve our under- One color cycle represents Faults s about 4 inches of subsidence. standing of the subsidence processes. A

Inc combination of scientic understanding relat re ive as 95 su in and careful management can minimize b g s id e V the subsidence that results from develop- n c a e NE VA DA ing our land and water resources. l l Map e area y —D.L. Galloway, D.R. Jones, S.E. Ingebritsen 15

REFERENCES Amelung, F., Galloway, D.L., Bell, J.W., Zebker, Galloway, D.L., Jones, D.R., and Ingebritsen, S.E., and its restoration: Delray Beach, Fla., St. Lucie H.A., and Laczniak, R.J., 1999, Sensing the ups and 1999, Land subsidence in the United States: U.S. Press, p. 85–115. downs of Las Vegas—InSAR reveals structural con- Geological Survey Circular 1182, 175 p. Stephens, J.C., Allen, L.H., Jr., and Chen, Ellen, 1984, trol of land subsidence and aquifer-system deforma- Galloway, D.L., Jones, D.R., and Ingebritsen, S.E., Organic soil subsidence, in Holzer, T.L., ed., Man- tion: Geology, v. 27, p. 483–486. 2000, Measuring land subsidence from space: U.S. induced land subsidence: Geological Society of Amer- Clawges, R. M., and Price, C. V., 1999, Digital Geological Survey Fact Sheet 051-00, 4 p. ica Reviews in Engineering Geology, v. 6, p. 107–122. data sets describing principal aquifers, surcial Lucas, R.E., 1982, Organic soils (Histosols)—Formation, White, W.B., Culver, D.C., Herman, J.S., Kane, T.C., geology, and ground-water regions of the contermi- distribution, physical and chemical properties and man- and Mylroie, J.E., 1995, Karst lands: American Sci- nous United States: U.S. Geological Survey Open- agement for crop production: Michigan State Univer- entist, v. 83, p. 450–459. File Report 99-77 [accessed Sept. 17, 1999 at URL sity Farm Science Research Report 435, 77 p. http://water.usgs.gov/pubs/ofr/ofr99-77]. Martinez, J.D., Johnson, K.S., and Neal, J.T., 1998, For more information on ground-water-resource Davies, W.E., and Legrand, H.E., 1972, Karst of the Sinkholes in evaporite rocks: American Scientist, v. issues and subsidence, please contact: United States, in Herak, M., and Stringeld, V.T., 86, p. 38–51. eds., Karst—Important karst regions of the northern Chief, Ofce of Ground Water hemisphere, p. 467–505. National Research Council, 1991, Mitigating losses U.S. Geological Survey from land subsidence in the United States: Washing- 411 National Center Ege, J.R., 1984, Mechanisms of surface subsidence ton, D. C., National Academy Press, 58 p. 12201 Sunrise Valley Drive resulting from solution extraction of salt, in Holzer, Snyder, G.H., and Davidson, J.M., 1994, Everglades Reston, VA 20192 T.L., ed., Man-induced land subsidence: Geological (703) 648-5001 Society of America Reviews in Engineering Geol- agriculture: Past, present, and future, in Davis, S.M., ogy, v. 6, p. 203–221. and Ogden, J.C., The Everglades—The ecosystem http://water.usgs.gov/ogw

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