What is land subsidence?
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 of organic soils, underground mining, hydrocompaction, natural compaction, sinkholes, and thawing permafrost (National Research Council, 1991). Three distinct processes account for most of the water-related subsidence--compaction of aquifer systems, drainage and subsequent oxidation of organic soils, and dissolution and collapse of susceptible rocks.
In the following video, California Water Science Land Subsidence Specialist, Michelle Sneed, talks about the sinking in the San Joaquin Valley that is occurring due to groundwater pumping.
How is land subsidence measured?
Measurements of elevations, aquifer-system compaction, and water levels are presented, interpreted, and integrated to improve understanding of the processes responsible for land-surface elevation changes. Elevations, and elevation changes, have been measured using Interferometric Synthetic Aperture Radar (InSAR), Continuous GPS (CGPS) measurements, campaign Global Positioning System (GPS) surveying, and spirit-leveling surveying.
Explore the data map!