Subsidences

Subsidences refer to the downward movement or settlement of the Earth's surface. The term encompasses a range of processes that reduce elevation relative to a reference level, varying in pace from gradual to sudden.

Causes include natural processes such as sediment compaction, tectonic subsidence, and karst dissolution; and human activities such as groundwater extraction, mining, oil and gas withdrawal, heavy construction loads, and landfilling. Changes in surface loading and hydrology can amplify subsidence.

Measurement and monitoring use satellite radar (InSAR), GNSS/GPS, leveling surveys, tiltmeters, and borehole extensometers. Rates are commonly expressed in millimeters per year, with differential subsidence producing tilting, foundation cracking, and damage to infrastructure.

Impacts include damage to buildings, roads, and utilities; changes to drainage and irrigation; increased flood risk in coastal or riverine areas; and substantial economic costs for mitigation and repair.

Prevention and mitigation involve reducing groundwater and other fluid withdrawals, using alternative water supplies, improved mine closure, soil stabilization techniques (grouting, compaction control), careful land-use planning, and structural adaptations in affected areas.

Notable examples are Mexico City, where aquifer depletion has caused significant subsidence; Jakarta, Indonesia, where groundwater withdrawal contributes to rapid sinking; and portions of the Venice region and the Netherlands’ delta, where subsidence interacts with sea-level rise.