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My uncle's house was swallowed by a sinkhole!

Picture of a sinkhole

Certain kinds of sinkholes can form without warning .... to bad if there is a house in the way!
Credit: Doug Gouzie

Luckily this is rare, but items like this have shown up on the evening's news. Sometimes humans are responsible for places where the land subsides and/or sinkholes develop. If large amounts of groundwater are pumped from an area that is composed of a thick layer of fine-grained material then the land can become more compacted once the water is removed. In other words, the water keeps the soil from settling, and once the water is gone, the soil settles -- too bad if there is a house on top.

Sinkholes are common where the rock below the land surface is limestone, carbonate rock, salt beds, or rocks that can naturally be dissolved by groundwater circulating through them. As the rock dissolves, spaces and caverns develop underground. Sinkholes are dramatic because the land usually stays intact for a while until the underground spaces just get too big. If there is not enough support for the land above the spaces then a sudden collapse of the land surface can occur. These collapses can be small or they can be huge and can occur where a house or road is on top.

Some parts of the country are susceptible to sinkholes -- places where the land is underlain by limestone that can be dissolved by groundwater. Also, a house could be sitting on a salt bed that dissolves, leaving a cavern in the ground. Some homeowners have become cave-dwellers overnight!