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Learn more about sinkholes.USGS Science Feature

The Science of Sinkholes



What is a "Sinkhole"?

Picture of a sinkhole that formed below part of a house.A sinkhole is an area of ground that has no natural external surface drainage--when it rains, all of the water stays inside the sinkhole and typically drains into the subsurface. Sinkholes can vary from a few feet to hundreds of acres and from less than 1 to more than 100 feet deep. Some are shaped like shallow bowls or saucers whereas others have vertical walls; some hold water and form natural ponds.

Typically, sinkholes form so slowly that little change is noticeable, but they can form suddenly when a collapse occurs. Such a collapse can have a dramatic effect if it occurs in an urban setting. This USGS picture shows a sinkhole that opened up too close to someone's home in Florida.

Areas prone to collapse sinkholes



Types of sinkholes

Since Florida is prone to sinkholes, it is a good place to use to discuss some different types of sinkholes and the geologic and hydrologic processes that form them. The processes of dissolution, where surface rock that are soluble to weak acids, are dissolved, and suffosion, where cavities form below the land surface, are responsible for virtually all sinkholes in Florida.

Dissolution sinkholes

Diagram of a sinkhole caused by dissolution of subsurface rock, generally limestone. Dissolution of the limestone or dolomite is most intensive where the water first contacts the rock surface. Aggressive dissolution also occurs where flow is focussed in preexisting openings in the rock, such as along joints, fractures, and bedding planes, and in the zone of water-table fluctuation where groundwater is in contact with the atmosphere.

Cover-subsidence sinkholes

Cover-subsidence sinkholes tend to develop gradually where the covering sediments are permeable and contain sand. In areas where cover material is thicker or sediments contain more clay, cover-subsidence sinkholes are relatively uncommon, are smaller, and may go undetected for long periods.

Cover-collapse sinkholes

Cover-collapse sinkholes may develop abruptly (over a period of hours) and cause catastrophic damages. They occur where the covering sediments contain a significant amount of clay. Over time, surface drainage, erosion, and deposition of sinkhole into a shallower bowl-shaped depression.

Diagram showing cover-collapse types of sinkholes.

Sinkholes can be human-induced



Take our groundwater true/false quiz. Groundwater true/false quiz

Sources and more information

 • Sinkholes, USGS Fact Sheet 2007-3060
 • Land Subsidence in the United States, U.S. Geological Survey Circular 1182
 • Land Subsidence in the United States, USGS Fact Sheet-165-00
 • Carbonate-rock aquifers, Aquifer Basics

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Page Last Modified: Thursday, 17-Jul-2014 11:24:28 EDT