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Land Subsidence in the United States - USGS Water Resources of the

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									                              GROUND-WATER RESOURCES FOR THE FUTURE


Land Subsidence in the United States
      Ground water is among the Nation’s most important natural resources. It
                                                                                                       Mining Ground Water
   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
                                                                                                       permanent subsidence and related ground
   a long-term perspective is needed to manage this valuable resource. This
                                                                                                       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,



A
                                                                                                       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
                                                                                                       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
                                                   Mendota, California.
to subsurface movement of earth materials.

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-
                                                           water from the Sacramento-San Joaquin                           ton, Texas, where 5 to 7 feet of subsidence
These include the Santa Clara Valley                                                                                       has occurred, were flooded during a storm in
in northern California, where early agri-                  Delta to basins affected by subsidence in                       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
                                                                         soils occur in the north-
                                                                                                      bilities of salt and gypsum permit cavities
                                                                         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
Figure 7. This building at the Everglades Experi-                                                     California today, one would be hard-pressed
ment Station was originally constructed at the
                                                    catastrophic sinkhole formation.
                                                                                                      to recognize that fewer than 75 years ago
land surface; latticework and stairs were added      Evaporite rocks underlie about 35 to
after substantial land subsidence.
                                                                                                      the land surface was nearly 30 feet higher
                                                    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-                                                           15
                                                                                                                       measurement resolution (sub-centimeter)
                                                            L




mation.
                                                                                                                       (Galloway and others, 2000) (g. 10).
                                                                a
                                                                s




                                                                                                                         Once subsidence is identied and
                                                                                                                       mapped, subsidence-monitoring programs
                                                                         V




                                                                                                                       can be implemented and scientic studies
                                                                           e




                                                                                      Las Vegas                        can be launched to improve our under-
                                                                              g




                     One color cycle represents
                                                                    Faults
                                                                                a




                    about 4 inches of subsidence.                                                                      standing of the subsidence processes. A
                                                                                  s




                                          I                                                                            combination of scientic understanding
                                    relativncrea
                                            es                                                                 95      and careful management can minimize
                                            sinbsiden




                                                                                                                       the subsidence that results from develop-
                                              u
                                               g




                                                                                             V




                                                                                                                       ing our land and water resources.
                                                     ce




                                                          N E VA DA
                                                                                               a
                                                                                                 l
                                                                                                  l e




                                                                Map
                                                                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].                                                                                For more information on ground-water-resource
                                                          Martinez, J.D., Johnson, K.S., and Neal, J.T., 1998,
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,                                                                                   Reston, VA 20192
 T.L., ed., Man-induced land subsidence: Geological       Snyder, G.H., and Davidson, J.M., 1994, Everglades
                                                           agriculture: Past, present, and future, in Davis, S.M.,                         (703) 648-5001
 Society of America Reviews in Engineering Geol-
 ogy, v. 6, p. 203–221.                                    and Ogden, J.C., The Everglades—The ecosystem                              http://water.usgs.gov/ogw

    Printed on recycled paper

								
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