Ground subsidence is a gradual settling or sudden sinking of the Earth’s surface caused by the removal or displacement of materials underground. It can happen slowly over years, dropping land by just a few millimeters annually, or it can occur abruptly when the ground collapses into a sinkhole. The process affects cities, farmland, and coastlines worldwide, and in many cases it’s irreversible.
How the Ground Sinks
Subsidence happens when underground support structures, whether rock, soil, or water pressure, weaken or disappear. The surface above has nothing holding it up, so it drops. The specific mechanism depends on what’s happening below.
The most widespread cause is groundwater pumping. Aquifers contain layers of fine-grained sediments like clays and silts made up of flat, plate-shaped grains. When these sediments are first deposited, the grains sit in random orientations with plenty of space between them to hold water. That water pressure helps support the weight of everything above. When pumping drops water levels to historically low points, the grains rearrange into compact stacks. These stacks take up less space and hold less water. The land above settles downward as a result, and because the grains can’t return to their original random arrangement, the compaction is permanent.
Other human activities trigger the same basic process through different paths. Underground mining removes rock and creates voids that eventually collapse. Draining wetlands and organic soils causes the exposed material to decompose and shrink. Oil and gas extraction reduces pressure in deep rock formations, allowing them to compact.
Natural Causes of Subsidence
Not all subsidence is human-caused. In regions built on soluble rock like limestone, gypsum, or salt deposits, groundwater slowly dissolves the rock over decades or centuries. This creates underground cavities that can collapse without warning, forming sinkholes. Geologists call these landscapes “karst terrain,” and they’re found across Florida, parts of Texas, and large stretches of the central United States.
Thawing permafrost is another natural driver, particularly in Alaska and northern Canada. As permanently frozen ground warms, ice within the soil melts and the ground compresses. Some areas of Alaska are sinking at rates up to 1 cm per year from this process alone. Tectonic forces and the slow, natural compaction of sediments in river deltas also contribute, though typically at rates too slow to notice without instruments.
Which Soils Are Most Vulnerable
Peat and clay are the two soil types most prone to subsidence, but they behave differently. Clay minerals carry a strong negative electrical charge on their surfaces, which influences how tightly particles attract or repel each other and how water moves between them. When pressure increases, water is squeezed from tiny pores between clay particles, and the soil compresses.
Peat is even more susceptible. Its fibers have larger pore spaces and a weaker internal structure compared to clay. As organic material in peat decomposes, the structure weakens further, making it easier for particles to rearrange and compress. This is a particular concern for cities built on river deltas, where thick layers of peat can sit beneath the surface. Interestingly, once peat has fully decomposed, the remaining material is actually less compressible than fresh, fibrous peat.
Where Subsidence Is Happening Fastest
Several U.S. cities are sinking at rates that have real consequences for infrastructure. The Houston-Galveston area in Texas has experienced subsidence rates up to 5 cm per year in certain zones due to decades of groundwater, oil, and gas extraction. The Phoenix metropolitan area and Las Vegas Valley have recorded rates up to 9 cm per year. Texas cities including Houston, Fort Worth, and Dallas show the highest measured subsidence rates among all U.S. cities studied, with averages exceeding 4 mm per year.
The Mississippi Delta is sinking at more than 1 cm per year, a problem made worse by the levees and dams that prevent the river from depositing fresh sediment to rebuild the land. Globally, major cities like Jakarta, Bangkok, and parts of coastal China face similar or worse rates, driven primarily by groundwater extraction for rapidly growing populations.
Why Subsidence Makes Flooding Worse
In coastal areas, subsidence and sea-level rise combine in a particularly damaging way. When the land drops while the ocean rises, the effective increase in water level relative to the ground is the sum of both. The Chesapeake Bay region, for example, experiences about 2 mm per year of subsidence from the slow rebound of Earth’s crust after the last ice age. That land sinking adds substantially to the area’s already high rates of relative sea-level rise.
What makes this especially challenging is that subsidence rates can vary dramatically over short distances. One neighborhood might be sinking twice as fast as one a few miles away, depending on the underlying geology and local water extraction. This creates uneven flood risk that standard sea-level projections don’t always capture. NASA’s sea-level monitoring now incorporates ground movement data for exactly this reason.
How Scientists Track Ground Movement
Detecting millimeter-scale changes in ground elevation over large areas requires satellite-based radar. A technique called Interferometric Synthetic Aperture Radar, or InSAR, works by bouncing radar signals off the Earth’s surface from orbit on repeated passes. By comparing the phase of the returned signal between passes, scientists can calculate how much the ground has moved vertically.
No single monitoring method works best everywhere. Recent research comparing different technologies found that in areas of heavy sinking, drone surveys produced the most accurate measurements. In zones of moderate sinking, one form of satellite radar (D-InSAR) had the lowest error. And in areas with subtle, peripheral movement, a time-series satellite method (SBAS) performed best, with measurement errors more than 25% lower than standard radar and over 83% lower than drones. Combining all three gives scientists a comprehensive picture of how the ground is moving across an entire region.
Slowing and Preventing Further Sinking
Because groundwater depletion is the leading cause of subsidence worldwide, the most effective prevention strategy is managing water levels underground. Managed aquifer recharge involves deliberately putting water back into aquifers through surface spreading (letting water soak in over large areas), infiltration basins, or injection wells that pump treated water directly into the ground. The EPA notes that injection wells are used where surface infiltration isn’t practical, such as in dense urban areas.
Houston offers a case study in what regulation can accomplish. After decades of severe sinking, the region established a subsidence district that restricted groundwater pumping and required a shift to surface water supplies. Subsidence rates in the most affected areas slowed significantly as a result, though the land that had already dropped did not recover.
That irreversibility is the core challenge. Once fine-grained sediments compact, the process cannot be undone. Prevention and early intervention matter far more than remediation. For areas already affected, engineering responses focus on adapting infrastructure: raising buildings, improving drainage systems, reinforcing foundations, and in coastal zones, building flood barriers calibrated to account for ongoing sinking.