What is a sinkhole?
Sinkholes are depressions or “holes” in the earth that form due to the collapse of bedrock beneath the soil. Simply put, sinkholes form when water erodes bedrock, creating a void (or underground cave) that eventually collapses. Occasionally, sinkholes may even reveal an underground stream or river that could have contributed to the collapse. Sinkholes are common in areas where the rock below the top layer of soil/clay is a carbonate rock (i.e. limestone, dolostone ,etc.), salt deposits, or other easily dissolving bedrock.
Sinkholes can develop suddenly, as the layer above the void tends to sustain itself long enough for a big collapse to occur. This can sometimes allow structures on the surface (houses, buildings, roads, etc.) to remain supported for a certain amount of time before it eventually collapsing.
The state of Florida has the highest rate of sinkhole occurrences in the country.
Are all sinkholes the same?
There are three main types of sinkholes:
Dissolution Sinkholes – develop when limestone bedrock is broken down by erosion from wind and surface water. When surface soil and clay recedes, it exposes the layer of rock allowing water erosion to form a bowl-shaped depression under the foundation of your home, sometimes resulting in structure destruction.
Cover-collapse sinkholes – occur quickly, over a period of hours, and cause catastrophic damages. They occur when the ground cover contains more clay than sand. Over time, surface elements cause an arched depression directly under the ground cover. When the space between the ground cover and the depression gets thin enough, a large collapse can occur.
Cover-Subsidence Sinkholes – develop when the ground cover above the bedrock contains more sand than clay. Sand can then filter and accumulate in the bedrock below, causing small depressions along the ground’s surface above. Cover-subsidence sinkholes can go undetected for years.
How do they form?
There are many reasons that a sinkhole can occur. Natural water drainage, water main breaks, extraction of groundwater, rise of the water table, and runoff cause underground areas to become unstable and collapse. Once the water causes the subterranean rock to erode, a sinkhole will begin to form.
Why should sinkholes not be ignored?
Sinkholes can be very detrimental to the structures above them. Even small sinkholes can jeopardize a buildings structure, putting stress on supporting sections and causing the building to become unstable. If this happens, it could result in a collapse, taking all structures with them.
How do I recognize sinkhole damage?
The early signs of sinkhole damage can be very subtle. Often times, many people don’t realize damage until it becomes more apparent. Cracks in the foundation or the building’s exterior are the most common signs of a sinkhole. Interior cracks and separations (especially windows and doorways) are also common signs of a sinkhole.