What is a sinkhole?

A sinkhole is a depression in the ground that has no natural external surface drainage. Basically, this means that when it rains, all of the water stays inside the sinkhole and typically drains into the subsurface.

Sinkholes are most common in what geologists call, “karst terrain.” These are regions where the types of rock below the land surface can naturally be dissolved by groundwater circulating through them. Soluble rocks include salt beds and domes, gypsum, and limestone and other carbonate rock. Florida, for instance, is an area largely underlain by limestone and is highly susceptible to sinkholes.

When water from rainfall moves down through the soil, these types of rock begin to dissolve. This creates underground spaces and caverns.

Sinkholes are dramatic because the land usually stays intact for a period of time 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.

Find more information about sinkholes at the USGS Water Science School.

Related Content

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USGS CoreCast
May 8, 2008

What's Up With Sinkholes?

A huge sinkhole in Texas begs a few questions about this fascinating and sometimes hazardous phenomenon, so we sit down with USGS geologist Randy Orndorff to learn more.

Image: Various Karst Features Along Peace River, Fl
January 1, 2008

Various Karst Features Along Peace River, Fl

Observing the small amount of flow going into Dover Sink.

Image: Various Karst Features Along Peace River, Fl
January 1, 2007

Various Karst Features Along Peace River, Fl

Monitoring levels at Gator Sink.

Image: Various Karst Features Along Peace River, Fl
January 1, 2002

Various Karst Features Along Peace River, Fl

Crevasses Sink spans approximately 25 ft across the river bed.

Image: Winter Park Florida Sinkhole of 1981
May 10, 1981

Winter Park Florida Sinkhole of 1981

Photo 15 of 15: Water level in sinkhole chimney stabilized since the previous day. View to south across the sinhole. In the following weeks and months, the water level in the sinkhole continued to rise, a likely result of the plugging of the conduit into the Floridan aquifer with the sinkhole debris, fill subsequently emplaced by the city, and natural consolidation

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Image: Winter Park Florida Sinkhole of 1981
May 9, 1981

Winter Park Florida Sinkhole of 1981

Photo 12 of 15: Water level has risen and is now apparent in sinkhole since pool collapse and house swallowed. View to south across the sinkhole. The rising water level is likely a result of the debris plugging the conduit into the Floridan aquifer. Water level is rising to assume a position more consistent with that of the surficial aquifer. (3 p.m.)

Image: Winter Park Florida Sinkhole of 1981
May 9, 1981

Winter Park Florida Sinkhole of 1981

Photo 5 of 15: House in a sinkhole. View to east across the sinkhole.

Image: Winter Park Florida Sinkhole of 1981
May 9, 1981

Winter Park Florida Sinkhole of 1981

Photo 6 of 15: Sinkhole chimney at approximately 12 noon. View to south across the sinkhole.

Image: Prairie Pothole Region

Prairie Pothole Region

Prairie Pothole Region landscape showing high wetland density.

Attribution: Ecosystems
Image shows a cave diver in a flooded cave

Cave Diver in a Flooded Cave

Cave passage and diver within a section of the Ox Bel Ha cave system where the current study was conducted. The guideline seen alongside the diver that provides a continuous route to the surface is one of many safety standard the divers follow. Photograph © HP Hartmann.

Image: Sinkhole in Frederick, Maryland

Sinkhole in Frederick, Maryland

Cover-collapse sinkhole in limestone near Frederick, Maryland (September 2003). Many sinkholes occur along highways where rainwater runoff is concentrated into storm drains and ditches increasing the rate of sinkhole development (note the sewer drain pipe beneath roadway).

Attribution: Natural Hazards