Land Subsidence

Science Center Objects

More than 80 percent of known land subsidence in the U.S. is a consequence of groundwater use, and is an often overlooked environmental consequence of our land and water-use practices. Increasing land development threatens to exacerbate existing land-subsidence problems and initiate new ones. Subsidence detection and mapping done by the USGS is needed to understand and manage our current and future land and water resources in areas where subsidence is a problem or may be in the future.

Image: Land Subsidence in the San Joaquin Valley

Approximate point of maximum subsidence in the San Joaquin Valley, California. The land surface subsided roughly 9 meters from 1925 to 1977 due to aquifer-system groundwater withdrawals. Signs on the telephone pole indicate the former elevations of the land surface in 1925 and 1955. (Credit: Richard Ireland)

BACKGROUND

Land subsidence is a gradual settling or sudden sinking of the Earth's surface due to removal or displacement of subsurface earth materials. The principal causes include:

  • aquifer-system compaction associated with groundwater withdrawals 
  • drainage of organic soils
  • underground mining
  • natural compaction or collapse, such as with sinkholes or thawing permafrost

Subsidence is a global problem, and in the United States more than 17,000 square miles in 45 States have been directly affected by subsidence1.

 

ROLE OF SCIENCE

The occurrence of land subsidence is seldom as obvious as it is in the case of catastrophic sinkholes or mine collapses. Where groundwater depletion is involved, subsidence is typically gradual and widespread. The detection of regional-scale subsidence has historically occurred with the identified movement of key benchmarks. Gazing out over the San Joaquin Valley, California, today one would be hard-pressed to recognize that some of the land surface was nearly 30 feet higher fewer than 75 years ago.

The tool of choice used to detect and map land-surface deformation is known as interferometric synthetic aperture radar (InSAR). InSAR uses repeat-pass radar images from Earth-orbiting satellites to monitor subsidence and uplift at incredible detail. Once subsidence is identified and mapped, assessments of the InSAR data can be done to improve our understanding of the subsidence processes. A combination of scientific understanding and careful natural-resource management can minimize the subsidence that results from developing our land and water resources.

 

RELATED USGS RESEARCH

 

ADDITIONAL RESOURCES