GEOL 118 Lecture Notes - Lecture 22: Subsidence, Pore Water Pressure, San Joaquin Valley
5 Apr 2016
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Document Summary
Slow- involves gradual compaction of sediment due to withdrawal of subsurface fluid (groundwater or oil) Usually recognized only after reached advanced stage (gradual effects) Example: san joaquin valley, ca; houston, tx; venice, italy; mexico city, mexico. Pumping of groundwater causes sediment compaction due to removal of buoyant support from fluid (< pore water pressure) Removing pore water transfers weight of overlying sediment from fluid to grains. Can occur due to pumping of oil and natural gas, which occurs much deeper (>km) Rapid- involves abrupt lowering of more localized land area. Associated with collapse of land over underground cavity. Can be caused by subsurface coal mining (human-induced) Rapid subsidence and underground cave can be caused by subsurface dissolution of soluble rock. Subsurface dissolution of rock can be natural, commonly worsened by human activities. Rare subsurface rock dissolution can be human-induced. Example: accidental drilling into underground salt mine.
