Man-Induced Land Subsidence
How would you feel if your land had sunk 9 m in the past 50 years because of human activity? It happened in the San Joaquin Valley. In fact, land subsidence has been caused by man’s activities in at least 37 of the 50 states of the United States and affects more than 40,000 km2 in this country alone. Data from a few sites where economic impact is documented suggest a total annual cost to the nation of more than $100 million; worldwide, the total economic impact is astounding and growing. These nine papers, dedicated to Joseph Fairfield Poland's life work, constitute a major contribution to measuring and understanding this problem. They are arranged in three categories: (1) fluid withdrawal from porous media; (2) drainage of organic soil; and (3) collapse into man-made and natural cavities.
Mechanisms of surface subsidence resulting from solution extraction of salt
Published:January 01, 1984
Extraction of soluble minerals, whether by natural or man-induced processes, can result in localized land-surface subsidence. The subsidence is caused by partial or total collapse of underground cavities resulting from dissolution of salt or other soluble evaporites. In many cases, subsidence is ultimately related to the strength limit of the overlying rocks that form the unsupported roof above the cavity. Downwarping results where strength of roof spans are exceeded. In other cases, collapse of the undermined roof causes stoping of the overburden rocks. If sufficient underground space is available for the loosely packed rock debris to collect, the void can migrate to the surface and produce surface subsidence, or in the extreme, catastrophic surface collapse. Another mechanism is subsurface erosion of susceptible layers (sandstone, silt, loess) overlying salt cavities. Ground water can erode and transport the loose material down subsidence-induced and natural cracks, or drill holes into the salt cavity. The voids formed in the higher eroded beds can then cause surface subsidence.