Land subsidence is a gradual settling or sudden sinking of the Earth's surface owing to subsurface movement of earth materials. The principal causes are aquifer-system compaction, drainage and decomposition of organic soils, underground mining, oil and gas extraction, hydrocompaction, natural compaction, sinkholes, and thawing permafrost (National Research Council, 1991).
Effects of land subsidence include damage to buildings and infrastructure such as roads and canals, increased flood risk in low-lying areas, and lasting damage to groundwater aquifers and aquatic ecosystems.
Explore an interactive USGS map to learn more about areas in California affected by subsidence.
The USGS California Water Science Center uses an integrated set of ground- and space-based measuring techniques and mathematical simulations to study land subsidence. Learn more about these studies and how they are providing information to water managers to help them develop, manage, and protect groundwater resources in a sustainable manner.
Drought indicators in the Central Valley include declining groundwater levels and associated land subsidence as measured and estimated via multiple techniques.
The USGS California Water Science Center measures land-surface elevations, and elevation changes, with a variety of land- and space-based scientific techniques, the most common being Interferometric Synthetic Aperture Radar (InSAR), continuous GPS (CGPS), and land-surface surveying methods.
Land subsidence in California has two primary causes: aquifer compaction due to excessive groundwater pumping, and decomposition of wetland soils exposed to air after wetland conversion to farmland. Effects include damage to aquifers, ecosystems, and infrastructure.
The USGS California Water Science Center develops and uses integrated hydrologic models to quantify the spatial and temporal extent of historical subsidence, predict future subsidence under various management scenarios, and help optimize surface water and groundwater use.