a) Land subsidence is the lowering of the land-surface elevation from changes that take place underground. Common causes of land subsidence from human activity are pumping water, oil, and gas from underground reservoirs, sinkholes, collapse of underground mines, drainage of organic soils, and initial wetting of dry soils. It happens in nearly every state in the United States of America. More than 17,000 square miles in 45 States, an area roughly the size of New Hampshire and Vermont combined, have been directly affected by subsidence.
b) Land subsidence causes many problems including changes in elevation and slope of streams, canals, and drains. Also, damage to bridges, roads, railroads, storm drains, sanitary sewers, canals, and levees. It can cause damage to private and public buildings and failure of well casings from forces generated by compaction of fine-grained materials in aquifer systems. In some coastal areas, subsidence has resulted in tides moving into low-lying areas that were previously above high-tide levels.
c) We could come up with alternate ways to deal with water underground which will help cut down the risk of subsidence becoming an issue. If we cut back on projects like digging holes and uprooting tress it would hopefully help prevent the possibility of subsidence. There's no real way to stop subsidence that we know of, all we can really do is try new things and hope that one day our homes and other beloved locations don't get sucked down into the Earth.
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