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Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →Land subsidence is the broad process of ground settling or sinking; a sinkhole is one localized form of ground collapse. Subsidence can develop across a wide area as underground materials compact, while sinkholes often form when water dissolves soluble rock and the ground above loses support. Either process can be gradual or sudden, and a crack by itself cannot identify the cause.
What is the difference between a sinkhole and land subsidence?
The U.S. Geological Survey (USGS) defines land subsidence as “a gradual settling or sudden sinking of the Earth’s surface owing to subsurface movement of earth materials.” A sinkhole is a particular kind of ground collapse within that broader category. In the USGS definition, it is a depression with no natural external surface drainage: rainwater collects in it and typically drains underground. USGS: What is the difference between a sinkhole and land subsidence?
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| Feature | Land subsidence | Sinkhole |
|---|---|---|
| Scope | Broad term for the ground surface settling or sinking because of movement or change in underground materials. | A localized depression or collapse; one form of subsidence or ground collapse. |
| Common mechanisms | Can result from aquifer-system compaction, drainage of organic soils, underground mining, hydrocompaction, natural compaction, sinkholes, or thawing permafrost. | Often forms when groundwater dissolves soluble bedrock, creating cavities, and the roof or overlying material loses support. |
| Typical setting | Can occur where aquifers compact, organic soils are drained, mines are present, or permafrost thaws. | Especially associated with karst terrain, where soluble rock such as limestone, gypsum, or salt is dissolved by water. |
| Tempo and scale | Groundwater-related subsidence is often gradual and widespread, but subsidence can also be sudden. | Collapse may be abrupt and localized, but the sinkhole-forming process can involve changes underground over time. |
The distinction is about the process and scale, not a rule that subsidence is always slow and sinkholes are always sudden. A sinkhole is one possible form of subsidence; subsidence also happens without a sinkhole.
How do subsidence and sinkholes form?
Subsidence: compaction, drainage, and other ground changes
One widespread cause is groundwater pumping. When pumping lowers water levels, fine-grained layers in an aquifer system can compact. Reduced pore volume can be largely nonrecoverable, permanently lowering the aquifer’s ability to store water. Other causes identified by the USGS include drainage of organic soils, underground mining, hydrocompaction, natural compaction, sinkholes, and thawing permafrost. USGS: Land subsidence in the United States
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Sinkholes: dissolution followed by loss of support
In karst terrain, groundwater can dissolve bedrock such as limestone and other carbonate rocks, gypsum, or salt. Cavities may develop underground; a collapse can follow when the roof or overlying material can no longer support the ground above. Changes in groundwater levels and increased water percolation can contribute, and human activity may trigger or intensify some collapses. Gypsum and salt dissolve more readily than limestone, although limestone is commonly associated with catastrophic sinkhole formation. USGS: What are sinkholes?
Where are these hazards more likely?
Sinkhole susceptibility is strongly related to geology. Karst areas with soluble rock are a key setting, and USGS says areas prone to sinkhole development are generally well known by state geological surveys. Other forms of subsidence are associated with conditions such as groundwater-dependent aquifers, drained organic soils, mining, or thawing permafrost. These broad associations cannot establish whether a particular property is at risk; local geology and groundwater conditions matter.
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What warning signs should you look for?
Visible changes can be worth documenting and reporting, but they are not a reliable stand-alone diagnosis. A USGS homeowner publication notes that concentric cracks can develop in smaller areas where compaction is occurring. Broad subsidence, however, may not be noticeable, and sinkholes can develop suddenly. A crack, depression, or other ground change does not by itself prove a sinkhole, and the absence of visible signs does not rule out subsidence. The reviewed USGS material does not establish a universal warning-sign checklist or a reliable consumer test. USGS Circular 1309: Land Subsidence in the United States
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- Record where and when you noticed a change, and whether it appears to be changing. Avoid treating that observation as a diagnosis.
- For local susceptibility information, contact the state geological survey or relevant local authority. For a specific property concern, seek qualified site-specific expertise.
- Do not rely on a consumer product or general-purpose measuring tool as a substitute for local geological information or a professional assessment.
What are the risks?
Subsidence can damage land and infrastructure. Where aquifer materials compact, lost pore space can permanently reduce groundwater storage capacity. A sinkhole collapse can occur over hours and cause catastrophic damage. The actual risk depends on local geology, groundwater conditions, land use, and the presence and extent of underground voids; a general explanation cannot predict the danger to a particular property.
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How common are subsidence and sinkhole collapses in the United States?
The USGS’s 2019 overview says more than 80 percent of known land subsidence in the United States is a consequence of groundwater use, and that more than 17,000 square miles in 45 states have been directly affected by subsidence. These figures describe U.S. conditions, not global rates. USGS: Land subsidence in the United States
There is no U.S. database of sinkhole collapses, so the USGS says a reliable national annual total is unavailable. Some state surveys track events, but many collapses are unreported or unobserved. USGS: How many sinkholes open up in a year?
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What should you do about a suspected ground change?
- Do not diagnose from appearance alone. Note the location and visible change; a surface crack or depression can have multiple explanations.
- Check local information. Contact your state geological survey or relevant local authority for information about known susceptibility and appropriate local reporting.
- Get a site-specific assessment if a property is involved. A qualified professional can assess conditions at the location; general hazard information cannot determine the status of an individual property.
Insurance coverage, reporting procedures, and emergency advice vary by location and are not established by the general USGS information cited here. Consult the relevant local authority and your insurer for those questions.
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