Karst Aquifers

Science Center Objects

Karst terrain is created from the dissolution of soluble rocks, principally limestone and dolomite. Karst areas are characterized by distinctive landforms (like springs, caves, sinkholes) and a unique hydrogeology that results in aquifers that are highly productive but extremely vulnerable to contamination.

What is Karst?

Karst aquifers are a vital groundwater resource in the United States. In the United States, about 40% of the groundwater used for drinking comes from karst aquifers.

Some karst areas in the United States are famous, such as the springs of FloridaCarlsbad Caverns in New Mexico, and Mammoth Cave in Kentucky, but in fact about 20 percent of the land surface in the U.S. is classified as karst. Other parts of the world with large areas of karst include China, Europe, the Caribbean, and Australia.

Karst hydrogeology is typified by a network of interconnected fissures, fractures and conduits emplaced in a relatively low-permeability rock matrix. Most of the groundwater flow and transport occurs through the network of openings, while most of the groundwater storage occurs in the matrix. As a result, most karst aquifers are highly heterogeneous and anisotropic, and much of karst research has focused on developing innovative approaches for better understanding and managing these valuable water resources.

Karst Map of the Conterminous United States - 2020

Map showing karst areas of the continental United States having sinkholes in soluble rocks (carbonates and evaporites), as well as insoluble volcanic rocks that contain sinkholes. The volcanic bedrock areas contain lava tubes that are voids left behind by the subsurface flow of lava, rather than from the dissolution of the bedrock. Hot spots of sinkhole activity are also shown in areas of greater susceptibility. Source: Progress toward a preliminary karst depression density map for the conterminous United States.

 

Principal Karst Aquifers

  • Arbuckle-Simpson aquifer (OK) — Underlies more than 500 square miles in south central Oklahoma and is the principal water source for about 40,000 people. Many springs and small karst features, but only a few air-filled caves.
  • Basin and Range and Bear River range carbonate aquifers (NV, UT) — Some fractured carbonate rocks beneath alluvial basin fill. Includes areas near Cedar Break Nat. Monument, Great Basin Nat. Park, and the Bear River Range.
  • Colorado Plateau karst (AZ)
  • Edwards Balcones Fault Zone aquifer (OK, TX) — Highly faulted and fractured carbonate rocks of Cretaceous age in an area of about 4,000 square miles in south-central Texas. Primary drinking-water supply for San Antonio, TX.
  • Edwards-Trinity Plateau aquifer (AR, OK, TX) — Consists of rocks of Cretaceous age that are present in an area of about 35,500 square miles in west-central Texas.
  • Upper Floridan and Biscayne aquifers (AL, GA, FL, MI, SC)
  • Madison aquifer (MT, ND, NE, SD, WY, and Canada)— An important water resource in the northern plains states, where surface-water supplies are limited and population is increasing. It is one of the largest confined aquifer systems in the U.S.
  • Midwest Paleozoic Carbonate aquifers (IA, IL, IN, MI, MN, OH, WI) — Karst developed in several Paleozoic aquifers that span the Midwest from Michigan to Tennessee. Contains some of the longest mapped caves in the world, including Kentucky's Mammoth Cave Nat. Park.
  • New England karst aquifers (MA, ME, VT) — Solution terrain in crystalline limestones and marbles mainly in northeastern Maine, western Vermont, and western Massachusetts.
  • Ozark Plateau karst aquifers (AR, KS, MO, OK) — Paleozoic carbonate rocks underlying several mid-continent states. Comprises two aquifers (Springfield and Ozark) and an intervening confining unit, and yields modest amounts of water.
  • Roswell Basin aquifer (NM) — An eastward-dipping carbonate aquifer overlain by a leaky evaporitic confining unit and an unconfined alluvial aquifer. Decades of intensive pumping have caused substantial declines in hydraulic head.
  • Pacific Northwest basalt aquifers (CA, ID, OR, WA) — Late Cenozoic basalt lava fields that contain lava tubes, fissures, open sinkholes, and caves formed by extrusion of the still-liquid portion of the lava.
  • Valley and Ridge, Piedmont, and Blue Ridge aquifers (AL, GA, MD, NC, PA, SC, TN, WV, VA) — Extensive areas of karst within complex geologic structures, resulting in highly variable karst-aquifer characteristics. Includes the Great Valley aquifer, an important water resource for many cities.

 

Karst Interest Group and Workshop

The USGS Karst Interest Group’s (KIG) mission is to encourage and support interdisciplinary collaboration and technology transfer among scientists working in karst areas. The 8th USGS KIG Workshop will be held virtually on October 19-21, 2021. See the Karst Interest Group Workshop webpage for more information, and for proceedings from previous meetings.