It is a frightening thought to imagine the ground below your feet or house suddenly collapsing and forming a big hole in the ground. Sinkholes rarely happen, but when they strike, tragedy can occur. Sinkholes happen when the ground below the land surface cannot support the land surface. They happen for many reasons; read on to educate yourself about sinkholes.
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Sinkholes
Credit: Ann Tihansky, USGS
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, as this picture shows, or they can be huge and can occur where a house or road is on top.
The most damage from sinkholes tends to occur in Florida, Texas, Alabama, Missouri, Kentucky, Tennessee, and Pennsylvania.
What is a "sinkhole"?
A sinkhole is an area of ground that has no natural external surface drainage--when it rains, 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.
Areas prone to collapse sinkholes
The map below shows areas of the United States where certain rock types that are susceptible to dissolution in water occur. In these areas the formation of underground cavities can form, and catastrophic sinkholes can happen. These rock types are evaporites (salt, gypsum, and anhydrite) and carbonates (limestone and dolomite). Evaporite rocks underlie about 35 to 40 percent of the United States, though in many areas they are buried at great depths.

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 suffusion, where cavities form below the land surface, are responsible for virtually all sinkholes in Florida.
DISSOLUTION SINKHOLES
Dissolution of the limestone or dolomite is most intensive where the water first contacts the rock surface. Aggressive dissolution also occurs where flow is focused 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.
Rainfall and surface water percolate through joints in the limestone. Dissolved carbonate rock is carried away from the surface and a small depression gradually forms. On exposed carbonate surfaces, a depression may focus surface drainage, accelerating the dissolution process. Debris carried into the developing sinkhole may plug the outflow, ponding water and creating wetlands. Gently rolling hills and shallow depressions caused by solution sinkholes are common topographic features throughout much of Florida.

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.
- Granular sediments spall into secondary openings in the underlying carbonate rocks.
- A column of overlying sediments settles into the vacated spaces (a process termed “piping”).
- Dissolution and infilling continue, forming a noticeable depression in the land surface.\
- The slow downward erosion eventually forms small surface depressions 1 inch to several feet in depth and diameter.
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. Over time, surface drainage, erosion, and deposition of sediment transform the steep-walled sinkhole into a shallower bowl-shaped depression.
- Sediments spall into a cavity
- As spalling continues, the cohesive covering sediments form a structural arch.
- The cavity migrates upward by progressive roof collapse.
- The cavity eventually breaches the ground surface, creating sudden and dramatic sinkholes.

Sinkholes can be human-induced
New sinkholes have been correlated to land-use practices, especially from groundwater pumping and from construction and development practices. Sinkholes 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.
The overburden sediments that cover buried cavities in the aquifer systems are delicately balanced by groundwater fluid pressure. The water below ground is actually helping to keep the surface soil in place. Groundwater pumping for urban water supply and for irrigation can produce new sinkholes in sinkhole-prone areas. If pumping results in a lowering of groundwater levels, then underground structural failure, and thus, sinkholes, can occur.

Do you think you know about groundwater?
Take our Groundwater true/false quiz, part of our Activity Center.
Sources and more information
- Sinkholes, USGS Fact Sheet 2007-3060
- Land Subsidence in the United States, USGS Circular 1182
- Land Subsidence in the United States, USGS Fact Sheet-165-00
- Karst in the United States: A Digital Map Compilation and Database, USGS Open-File Report 2014–1156
- Carbonate-rock aquifers, USGS Aquifer Basics website
Quiz icon made by mynamepong from www.flaticon.com
Want to learn more about sinkholes? Follow me to the Land Subsidence website!
Below are other science topics associated with sinkholes and land subsidence.
Groundwater Information by Topic
Aquifers and Groundwater
Infiltration and the Water Cycle
Land Subsidence
Groundwater True/False Quiz
Groundwater Storage and the Water Cycle
How the U.S. Geological Survey Monitors Water
Groundwater Flows Underground
Below are publications associated with groundwater, sinkholes and land subsidence.
A primer on ground water
Land subsidence in the United States
Measuring land subsidence from space
Land subsidence in the United States
Ground water and the rural homeowner
Below are news stories associated with sinkholes and land subsidence.
Below are FAQ associated with sinkholes and land subsidence.
What is the difference between a sinkhole and land subsidence?
Sinkholes are just one of many forms of ground collapse, or subsidence. Land subsidence is a gradual settling or sudden sinking of the Earth’s surface owing to subsurface movement of earth materials. The principal causes of land subsidence are aquifer-system compaction, drainage of organic soils, underground mining, hydrocompaction, natural compaction, sinkholes, and thawing permafrost. Land...
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...
How many sinkholes open up in a year?
There is no database of sinkhole collapses for the United States, so these data are unavailable. Some individual state geologic surveys track reported collapses within their state. Many sinkhole collapses are not reported to authorities or news organizations, and many occur in rural areas where they are unobserved. Learn more: USGS Water Science School - Sinkholes
- Overview
It is a frightening thought to imagine the ground below your feet or house suddenly collapsing and forming a big hole in the ground. Sinkholes rarely happen, but when they strike, tragedy can occur. Sinkholes happen when the ground below the land surface cannot support the land surface. They happen for many reasons; read on to educate yourself about sinkholes.
• Water Science School HOME • Groundwater topics •
Sinkholes
More than 110 sinkholes formed in the Dover area of Florida during a freeze event in January 2010. Ground water levels dropped to record-setting lows as farmers pumped water to irrigate their plants for protection from the cold temperatures. The sinkholes destroyed homes, roads and sections of cultivated areas.
Credit: Ann Tihansky, USGSSinkholes 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, as this picture shows, or they can be huge and can occur where a house or road is on top.
The most damage from sinkholes tends to occur in Florida, Texas, Alabama, Missouri, Kentucky, Tennessee, and Pennsylvania.
What is a "sinkhole"?
A sinkhole is an area of ground that has no natural external surface drainage--when it rains, 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.
Areas prone to collapse sinkholes
The map below shows areas of the United States where certain rock types that are susceptible to dissolution in water occur. In these areas the formation of underground cavities can form, and catastrophic sinkholes can happen. These rock types are evaporites (salt, gypsum, and anhydrite) and carbonates (limestone and dolomite). Evaporite rocks underlie about 35 to 40 percent of the United States, though in many areas they are buried at great depths.
Sources/Usage: Public Domain. Visit Media to see details.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 suffusion, where cavities form below the land surface, are responsible for virtually all sinkholes in Florida.
DISSOLUTION SINKHOLES
Dissolution of the limestone or dolomite is most intensive where the water first contacts the rock surface. Aggressive dissolution also occurs where flow is focused 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.
Rainfall and surface water percolate through joints in the limestone. Dissolved carbonate rock is carried away from the surface and a small depression gradually forms. On exposed carbonate surfaces, a depression may focus surface drainage, accelerating the dissolution process. Debris carried into the developing sinkhole may plug the outflow, ponding water and creating wetlands. Gently rolling hills and shallow depressions caused by solution sinkholes are common topographic features throughout much of Florida.
Sources/Usage: Public Domain. Visit Media to see details.Source: Land Subsidence in the United States, USGS 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.
- Granular sediments spall into secondary openings in the underlying carbonate rocks.
- A column of overlying sediments settles into the vacated spaces (a process termed “piping”).
- Dissolution and infilling continue, forming a noticeable depression in the land surface.\
- The slow downward erosion eventually forms small surface depressions 1 inch to several feet in depth and diameter.
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.
Sources/Usage: Public Domain. Visit Media to see details.Source: Land Subsidence in the United States, USGS 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. Over time, surface drainage, erosion, and deposition of sediment transform the steep-walled sinkhole into a shallower bowl-shaped depression.
- Sediments spall into a cavity
- As spalling continues, the cohesive covering sediments form a structural arch.
- The cavity migrates upward by progressive roof collapse.
- The cavity eventually breaches the ground surface, creating sudden and dramatic sinkholes.
Sources/Usage: Public Domain. Visit Media to see details.Source: Land Subsidence in the United States, USGS Sinkholes can be human-induced
New sinkholes have been correlated to land-use practices, especially from groundwater pumping and from construction and development practices. Sinkholes 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.
The overburden sediments that cover buried cavities in the aquifer systems are delicately balanced by groundwater fluid pressure. The water below ground is actually helping to keep the surface soil in place. Groundwater pumping for urban water supply and for irrigation can produce new sinkholes in sinkhole-prone areas. If pumping results in a lowering of groundwater levels, then underground structural failure, and thus, sinkholes, can occur.
Sources/Usage: Some content may have restrictions. Visit Media to see details.Do you think you know about groundwater?
Take our Groundwater true/false quiz, part of our Activity Center.Sources and more information
- Sinkholes, USGS Fact Sheet 2007-3060
- Land Subsidence in the United States, USGS Circular 1182
- Land Subsidence in the United States, USGS Fact Sheet-165-00
- Karst in the United States: A Digital Map Compilation and Database, USGS Open-File Report 2014–1156
- Carbonate-rock aquifers, USGS Aquifer Basics website
Quiz icon made by mynamepong from www.flaticon.com
Want to learn more about sinkholes? Follow me to the Land Subsidence website!
- Science
Below are other science topics associated with sinkholes and land subsidence.
Groundwater Information by Topic
Groundwater is one of our most valuable resources—even though you probably never see it or even realize it is there. There is water somewhere beneath your feet no matter where on Earth you live. Groundwater starts as precipitation, just as surface water does, and once water penetrates the ground, it continues moving, sometimes quickly and sometimes very slowly. Eventually groundwater emerges back...Aquifers and Groundwater
A huge amount of water exists in the ground below your feet, and people all over the world make great use of it. But it is only found in usable quantities in certain places underground — aquifers. Read on to understand the concepts of aquifers and how water exists in the ground.Infiltration and the Water Cycle
You can't see it, but a large portion of the world's freshwater lies underground. It may all start as precipitation, but through infiltration and seepage, water soaks into the ground in vast amounts. Water in the ground keeps all plant life alive and serves peoples' needs, too.Land Subsidence
More than 80 percent of known land subsidence in the U.S. is a consequence of groundwater use, and is an often overlooked environmental consequence of our land and water-use practices. Increasing land development threatens to exacerbate existing land-subsidence problems and initiate new ones. Subsidence detection and mapping done by the USGS is needed to understand and manage our current and...Groundwater True/False Quiz
How much do you know about the water below your feet? Take our Groundwater True/False Quiz and find out.Groundwater Storage and the Water Cycle
The ground stores huge amounts of water and it exists to some degree no matter where on Earth you are. Lucky for people, in many places the water exists in quantities and at depths that wells can be drilled into the water-bearing aquifers and withdrawn to server the many needs people have.How the U.S. Geological Survey Monitors Water
There are many pieces of equipment, both mechanical and electronic, that are installed at stream-monitoring sites all around the world to measure, record, and transmit both water-quantity and water-quality information. The U.S. Geological Survey (USGS) monitors "real-time" streamflow and water-quality conditions for thousands of streams nationwide.Groundwater Flows Underground
Millions of cubic miles of water exists in the ground. You can't see it, but not only is it there, it is always moving around -- mostly downward, but also horizontally. Moving groundwater helps keep rivers full of water and allows for people to draw out water via wells. Moving groundwater is an important part of the water cycle. - Publications
Below are publications associated with groundwater, sinkholes and land subsidence.
A primer on ground water
Most of us don't have to look for water. We grew up either in big cities where there was a public water supply, or in small towns or on farms where the water came from wells. But there are some people to whom finding a new supply of water is vitally important.AuthorsHelene L. Baldwin, C. L. McGuinnessLand subsidence in the United States
No abstract available.AuthorsDevin L. Galloway, David R. Jones, S. E. IngebritsenMeasuring land subsidence from space
No abstract available.AuthorsDevin L. Galloway, David R. Jones, S. E. IngebritsenLand subsidence in the United States
This report explores the role of science in defining and understanding subsidence problems, and shows that the optimal use of our land and water resources may depend on improved scientific understanding to minimize subsidence. More than 80 percent of the identified land subsidence in the Nation is a consequence of human impact on subsurface water, and is an often overlooked environmental consequenAuthorsDevin L. Galloway, David R. Jones, S. E. IngebritsenGround water and the rural homeowner
As the salesmen sang in the musical The Music Man, "You gotta know the territory." This saying is also true when planning to buy or build a house. Learn as much as possible about the land, the water supply, and the septic system of the house before buying or building. Do not just look at the construction aspects or the beauty of the home and surroundings. Be sure to consider the environmental condAuthorsRoger M. Waller - News
Below are news stories associated with sinkholes and land subsidence.
- FAQ
Below are FAQ associated with sinkholes and land subsidence.
What is the difference between a sinkhole and land subsidence?
Sinkholes are just one of many forms of ground collapse, or subsidence. Land subsidence is a gradual settling or sudden sinking of the Earth’s surface owing to subsurface movement of earth materials. The principal causes of land subsidence are aquifer-system compaction, drainage of organic soils, underground mining, hydrocompaction, natural compaction, sinkholes, and thawing permafrost. Land...
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...
How many sinkholes open up in a year?
There is no database of sinkhole collapses for the United States, so these data are unavailable. Some individual state geologic surveys track reported collapses within their state. Many sinkhole collapses are not reported to authorities or news organizations, and many occur in rural areas where they are unobserved. Learn more: USGS Water Science School - Sinkholes