Nature
Subsidence is the lowering or collapse of the land surface either locally or over broad regional areas. Subsidence is usually not spectacular or catastrophic in itself but can cause great economic losses. It is caused by a large number of natural and man-made activities. Natural processes causing subsidence include: the dissolving of limestone and other soluble materials; earthquakes; global warming; and volcanic activity. Man-induced subsidence occurs mainly with the withdrawal of oil, gas or water; and has increased dramatically since 1940. Because underground fluids fill intergranular spaces and support sediment grains, removal of such fluids results in a loss of grain support, reduction of intergranular void spaces, and compaction of clays. The land surface commonly subsides wherever widespread sub-surface compaction has taken place, causing damage to canals, aqueducts, sewer systems and pipelines, and increasing the probability of flooding in some areas.
Claim
Sinking of soil is one of the biggest engineering problems any city can face.