What are Sinkholes?

sinkholes in Missouri


What are Sinkholes, How Big Are They, & Where do They Occur?

This post explains what sinkholes are and why they occur, describes their effects on buildings, and gives building and site inspection advice useful in identifying areas where there is an increased risk on properties.


In general terms, a sinkhole is any sudden subsidence of the earth. In more technical terms, a true “sinkhole” is a subsidence or soil collapse caused by a combination of water eroding supporting soils, rock, or limestone, and an underlying geological structure or material that is particularly vulnerable to dissolving in water.

But consistent with their cause and the underlying soil and geology, the actual cause, and the size and dangers vary widely, from a small subsidence over an abandoned septic tank or swimming pool to enormous giants that swallow towns.

Here we describe this variety of sinkholes and soil subsidences, their locations, causes, sizes, and impact or dangers.

Synonyms and similar terms for sinkholes include: shake hole, swallow hole, swallet, doline, cenote, moulin, and glacier mill.

Urban or suburban sinkholes due to burst water mains, sewer lines, or storm drains can occur almost anywhere. Here we focus on other sinkhole types and causes including sinkholes due to geological formations, types of rock (karst formations), or due to human activities such as mining. We also discuss here sinking buildings from causes other than sinkholes.

“Sinkholes” that are not verified by a licensed professional geologist or geotechnical engineer to be a true sinkhole are also described in various publications as subsidence incidents.


sink hole in Kansas City Missouri


The bare minimum that a property owner needs to know about sinkholes or any other sudden subsidence of soils at a property is that these conditions might be very dangerous.

Someone falling into a sinkhole or a collapsing septic tank could be seriously injured or even die.

If a suspicious hole, subsidence, or depression appears at a property the owner should rope off and prevent access to the area to prevent anyone from falling into the opening, and then should seek prompt assistance from a qualified expert, geotechnical engineer, septic contractor, excavator, or the like.

The photograph of a sinkhole opening in a residential yard in Pennsylvania is from Kochanov, W.E., and illustrates the child hazard or even adult sinkhole hazard that can be formed by stormwater drainage.

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