What is subsidence?
by 
scymitar72
ANSWERS: 3
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Land subsidence is the lowering of the land-surface elevation from changes that take place underground
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More specifically, the processes occuring underground include collapse (as in subsidence caused by coal mine collapse in Pennsylvania and sinkhole collapse in Florida), and compaction. Compaction in turn results from exclusion of water by overburden pressure (as in the Mississippi River delta) and by the extraction of fluids including hydrocarbons (Long Beach harbor) and water (California Central Valley).
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1-26-2017 Word Origin & History subside 1681, "to sink to the bottom," from L. subsidere "settle, sink, sit down or remain," from sub "down" + sidere "to settle," related to sedere (see sit). Meaning "to sink to a lower level, be reduced" is from 1706. (Does not have to refer to ground, although that is the most common use.)
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