How to Spot a Sinkhole

A sinkhole is a ground-surface depression that forms when water dissolves rock near or at the earth’s surface. When the subterranean void weakens support of the overlying earth, it can result in a monstrosity that can literally swallow up a whole house. A less noticeable, much smaller sinkhole can also do its fair share of damage, wreaking havoc on the plumbing and undermining a building’s foundation. Often, one can spot the signs of a developing sinkhole before the hole appears.

The infographic guide below will walk you through how sinkholes are formed, where they are formed and how to spot them to prevent further damage.

Related program: B.A. in Geology

UF Online Infographic: How to Spot a Sinkhole

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A sinkhole is a naturally occurring geological hazard that can worsen rapidly and cause devastating damage. It can cause extensive damage to roads and structures resulting in costly repairs. It can also compromise water supplies by draining unfiltered water from wetlands, lakes and streams directly into the underground water supply.

Sinkholes mostly appear in areas where the surface rock is limestone, which easily erodes due to water movement. Erosion rates are highest in high rainfall areas. About 20% of the surface land in the United States is susceptible to sinkholes, with the most damage occurring in Kentucky, Florida, Alabama, Texas, Missouri, Pennsylvania, and Tennessee.

Sinkhole Triggers

Sometimes, a sinkhole may seem to have appeared overnight; however, many of them evolve over hundreds or even thousands of years. They develop long before any surface evidence is visible. Essentially, sinkholes are what people see on the ground surface due to a hole in the rock below. However, several things can trigger a sinkhole.

A range of factors, man induced and natural, can trigger a sinkhole collapse. Adding weight, such as a building, above cavities can also trigger a sinkhole. Human induced sinkholes occur because of land use practices, especially construction and water pumping. For example: artificially building ponds of surface water, drilling additional wells in an area, over-pumping existing wells, construction of structures and roadways, and building of housing developments. Other human induced triggers include abandoned septic tanks, decaying organic material, and collapsed mines.

Surface flooding, heavy rain, and drought are examples of natural triggers. Drought can leave cave roofs unprotected and lower the water table, which can trigger sinkholes. Heavy rainfall, on the other hand, can dissolve subsurface rock, thereby creating underground cavities. This often happens in areas where the subsurface rock is limestone, carbonate rock, dolomite, or salt beds that can naturally dissolve due to circulating groundwater.

Sinkhole Prone Areas

They mostly occur in karst terrain. This is a landscape formed from the breakup of soluble rocks, including limestone, gypsum and dolomite. They form when a fracture in the sub--surface rock enlarges, which can increase the risk of groundwater contamination. Twenty percent of the United States’ land surface is karst. One of the most famous karst areas in the country is Kentucky. On February 12, 2014, for example, a sinkhole opened under the floor of the National Corvette Museum in Bowling Green, Kentucky, swallowing eight one-of-a-kind corvettes, rails, and display stands.

Types of Sinkholes

There are three main types: solution sinkholes, cover collapse sinkholes, and cover subsidence sinkholes. Solution sinkholes happen in areas where the limestone rock bed is covered by a thin layer of permeable land and soil or is exposed at land surface. Cover subsidence sinkholes, on the other hand, are relatively permeable and non--cohesive, and individual grains of sand move sequentially downward to replace other grains of sand that have themselves moved downward to take up spaces previously held by dissolved limestone. Finally, cover collapse sinkholes take place in areas where a cavity develops in the limestone, and continues to enlarge to a size such that the surface cover can no longer support its own weight.

Some of the most famous sinkholes include the Devil’s Sinkhole in Edward’s County, Texas, the Daisetta Sinkhole in Texas, Winter Park in Florida, and Seffner, which is also in Florida. The Daisetta, for example, was a monster sinkhole measuring 900 feet wide by 400 feet deep. The Winter Park sinkhole was also big, measuring 350 feet wide by 75 feet deep. The Edward’s County and Seffner sinkholes were smaller, measuring 40ft by 60ft wide by 400ft deep, and 20ft across by 50ft deep respectively.

How to Spot a Sinkhole

Some of the warning signs that can signify that there is a sinkhole include structural cracks in floors and walls, windows and doors that do not close properly and cloudy or muddy well water. Signs of a sinkhole on the property include exposure of previously business items, such as fence posts and foundations, vegetation that wilts and dies as the sinkhole draws away essential water, and a circular pattern of ground cracks.

Other signs include the formation of small ponds after heavy rainfall, falling or slumping fence posts or trees, interrupted electrical service or plumbing due to damaged utility lines, and gullies that form as soil is carried towards the sinkhole.