Cover-collapse sinkholes Ĭover-collapse sinkholes or "dropouts" form where so much soil settles down into voids in the limestone that the ground surface collapses.
Cover-subsidence sinkholes Ĭover-subsidence sinkholes form where voids in the underlying limestone allow more settling of the soil to create larger surface depressions. Soil settles down into the enlarged openings forming a small depression at the ground surface. Dissolution enlarges natural openings in the rock such as joints, fractures, and bedding planes. Solution or dissolution sinkholes form where water dissolves limestone under a soil covering. Some sinkholes form when the land surface is changed, such as when industrial and runoff-storage ponds are created the substantial weight of the new material can trigger a collapse of the roof of an existing void or cavity in the subsurface, resulting in development of a sinkhole.Ĭlassification Solution sinkholes Sinkholes can also form when natural water-drainage patterns are changed and new water-diversion systems are developed. They can also occur from the overpumping and extraction of groundwater and subsurface fluids. More commonly, collapses occur in urban areas due to water main breaks or sewer collapses when old pipes give way. Main article: Pinge Collapse formed by rainwater leaking through pavement and carrying soil into a ruptured sewer pipe.Ĭollapses, commonly incorrectly labeled as sinkholes, also occur due to human activity, such as the collapse of abandoned mines and salt cavern storage in salt domes in places like Louisiana, Mississippi and Texas, in the United States of America. On 2 July 2015, scientists reported that active pits, related to sinkhole collapses and possibly associated with outbursts, were found on the comet 67P/Churyumov-Gerasimenko by the Rosetta space probe. Then, a sudden collapse of the land surface can occur. These sinkholes can be dramatic, because the surface land usually stays intact until there is not enough support. Sinkholes also occur in sandstone and quartzite terrains.Īs the rock dissolves, spaces and caverns develop underground. Sinkholes are common where the rock below the land surface is limestone or other carbonate rock, salt beds, or in other soluble rocks, such as gypsum, that can be dissolved naturally by circulating ground water. In the case of exceptionally large sinkholes, such as the Minyé sinkhole in Papua New Guinea or Cedar Sink at Mammoth Cave National Park in Kentucky, an underground stream or river may be visible across its bottom flowing from one side to the other. Occasionally a sinkhole may exhibit a visible opening into a cave below. For example, groundwater may dissolve the carbonate cement holding the sandstone particles together and then carry away the lax particles, gradually forming a void. Sinkholes often form through the process of suffosion. The formation of sinkholes involves natural processes of erosion or gradual removal of slightly soluble bedrock (such as limestone) by percolating water, the collapse of a cave roof, or a lowering of the water table. These caves may drain into tributaries of larger rivers. Sinkholes that capture drainage can hold it in large limestone caves. Sinkholes may capture surface drainage from running or standing water, but may also form in high and dry places in specific locations.
Formation Sinkholes near the Dead Sea, formed when underground salt is dissolved by freshwater intrusion, due to continuing sea-level drop. Sinkholes may form gradually or suddenly, and are found worldwide. Sinkholes are usually circular and vary in size from tens to hundreds of meters both in diameter and depth, and vary in form from soil-lined bowls to bedrock-edged chasms. Most sinkholes are caused by karst processes – the chemical dissolution of carbonate rocks, collapse or suffosion processes. Sink and stream sink are more general terms for sites that drain surface water, possibly by infiltration into sediment or crumbled rock. A cenote is a type of sinkhole that exposes groundwater underneath. The term is sometimes used to refer to doline, enclosed depressions that are locally also known as vrtače and shakeholes, and to openings where surface water enters into underground passages known as ponor, swallow hole or swallet. For other meanings, see Doline (disambiguation).Ī sinkhole is a depression or hole in the ground caused by some form of collapse of the surface layer.
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