Subsidence and caving in

Subsidence consists of a process whereby the ground gradually subsides, due to geological factors, but aggravated by the action of man.

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This phenomenon, liable to involve areas to differing extent , is generally caused by geological factors, but has been locally aggravated by the action of man over the last few decades, reaching dimensions exceeding those of natural origin.

Subsidence. Subsidence produced or aggravated by anthropogenic actions can be had by withdrawing water from the subsurface, gas or oil extractions, load of large buildings, extraction of solids, etc: the total degrees can even be for some metres in this case.Natural subsidence is caused by multiple factors: tectonic movements, magma cooling down under the Earth’s crust, sedimentary subsidence, etc.; vertical movements of a natural type may reach degrees of some millimetres per year.

Sinkholes. Rapid caving in (sinkholes) is a problem that only resembles subsidence to a certain extent, but contrary to the former has important repercussions on civil protection. These phenomena are caused by natural cavities in the subsurface as well as cavities created by man since ancient times (underground quarries, places used for various purposes, deposits, waterworks, sewage pipes, drains, etc.).

In Italy. Progressive subsidence phenomena have occurred along the Adriatic coastline from Rimini to Venice in our country, especially around the Po estuary, but also around urban agglomerates such as Milan, Bologna and Modena: above all in the latter areas due to extracting water from the subsurface. More recent cases have been reported in Puglia, at Piana di Sibari and Pianura Pontina.
What is more there are frequent problems of instability caused by underground cavities, often causing considerable material damage and, in many cases, even the loss of human lives in Italy.

Prevention. The underground cavity-related risk is particularly common in large built up areas where the action of human beings resulted in creating holes in the subsurface, mostly long lost and forgotten, above all due to the uncontrolled growth of built up areas over the last few decades.
Preventive-related measures to be implemented essentially consist in a correct management of water resources, avoiding excessive withdrawal from the aquifers, and in a disciplined planning of the extractive activities.