A sinkhole may also be known as a sink, shake hole, swallow hole, swallet, doline or cenote, is a natural depression or hole in the Earth's surface caused by karst processes.
These can be chemical dissolution of carbonate rocks or suffosion processes. For example in sandstone. Sinkholes may vary in size from 1 to 600 meters (3.3 to 2,000 ft) both in diameter and depth, and vary in form from soil-lined bowls to bedrock-edged chasms. They may be formed gradually or suddenly, and are found worldwide. These terms are often used interchangeably, though many distinguish between features a surface stream flows into and features with no such input. Only the former are described as sinks, swallow holes or swallets.
Sinkholes may capture surface drainage for running or standing water, but may also form in currently high and dry locations. The mechanisms of formation involve natural process 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.
Sinkholes often form also through the process of suffosion. Groundwater may dissolve the carbonate cement holding the sandstone particles together and then carry away particles, gradually forming a void. Occasionally a sinkhole may exhibit a visible opening into a cave below. In the case of exceptionally large sinkholes, such as Minyé sinkhole in Papua New Guinea or Cedar Sink at Mammoth Cave National Park, USA, a stream or river may be visible across its bottom flowing from one side to the other.
Sinkholes are common where the rock below the land surface is limestone or other carbonate rock, salt beds, or rocks that can naturally be dissolved by circulating ground water. As the rock dissolves, spaces and caverns develop underground. These sinkholes can be dramatic because the surface land usually stays intact until there is not enough support. Then, a sudden collapse of the land surface can occur.
Sinkholes also form from human activity. Sinkholes can occur in urban areas due to water main breaks or sewer collapses when pipes give way. They can also occur from the overpumping and extraction of groundwater and subsurface fluids. They can also form when natural water-drainage patterns are changed and new water-diversion systems are developed.
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 an underground collapse of supporting material, thus, causing a sinkhole.
