A sinkhole is a hole in the ground which opens due to a collapse of the surface layer of the ground, whether dirt or a road. Other names for a sinkhole are sink, shalehole, swallet, swallow hole, cenote, and doline. Usually, sinkholes develop over time, but sometimes they occur quickly. The ones which happen quickly can swallow cars and homes.

The first type of sinkhole is a dissolution or solution sinkhole. In this type of sinkhole, there is not much soil or plant growth over the bedrock underground. Water gradually flows into cracks in the bedrock and dissolves it. A hole or depression occurs. These can become ponds if debris builds up around the edge. These are not dangerous unless the pond drains suddenly if water escapes from the bottom of the pond.

The second type of sinkhole is a cover-subsidence sinkhole. With this type of sinkhole, sand instead of water seeps down through cracks in the bedrock causing a depression. This type of sinkhole is usually gradual from erosion.

The third type of sinkhole which is very dangerous is called the cover-collapse sinkhole. The bedrock is not covered by sand or a light film of dirt but by clay. Under the clay, an underground cavern is caused by water dissolving the rock. Then ground sediment erodes from the bottom of the cavern. The layer of rock between the ground clay and the cavern begins to dissolve and a hole opens up suddenly. Any structure, car or road in that spot falls into the hole.

The area's most susceptible to sinkholes are those where the rock underground is dissolvable. Sinkholes occur most frequently in Texas, Florida, Tennessee, Pennsylvania, Alabama, Missouri, and Kentucky.

Often there are warning signs. Fence posts may begin to lean, the seismic activity may occur, such as tremors in the ground, and foundations of buildings or trees may become exposed. A clue that the ground is falling can be seen when certain plant life collects in a pond in a circle. Man-made structures may develop cracks. Chimney holes are signs that a sinkhole is developing. They are deep holes with steep sides. The presence of such a hole should be reported to the local government.

Sinkholes can also appear when underground water pipes leak and erode the soil from under roadways. This happens when local entities fail to inspect water pipes due to lack of money. A 55,000-pound truck fell into a sinkhole in Oakwood, Georgia, in January 2017. It was sitting in a parking lot of an auto shop. A crumbling storm drain was the cause of this sinkhole.

Sinkholes are not usually fatal, but one opened in 2013 under the bedroom of Jeremy Bush in Seffner, Florida. He fell in, was covered by dirt immediately and could not be recovered. In February 2014, at the National Corvette Museum in Kentucky, eight Corvettes fell into a sinkhole.

In 2012, an underground mine collapsed in Louisiana, opening a natural underground oil reservoir. This released oil, methane and hydrogen sulfide into the air. 350 people had to be evacuated. A collapsed old mine shaft caused a sinkhole to appear in the backyard of an Australian family in 2016.

Sinkholes in caves or oceans which are filled with water are called blue holes. The deepest blue hole with an underwater entrance is in the Bahamas. The largest in the world is 1286 feet deep and is in Pozzo del Merro, Italy. Tourists love to visit and see these sinkholes. Pollution from these visitors contaminates the water because of fuel leakage from cars and runoff from parking lots.

A: Oceanic holes
B: Blue holes
C: Sea holes
D: Chimney holes

A: Water
B: Clay
C: Sand
D: Garbage

A: Longitudinal holes
B: Chimney holes
C: Blue holes
D: Cave holes

A: Sink
B: Doline
C: Shalehole
D: Cavern pond

A: Sand
B: Water
C: Clay
D: Ice

A: People are never killed from a sinkhole.
B: Sinkholes occur frequently in Florida.
C: Sinkholes can become ponds.
D: Tourists love to visit sinkholes.

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