What are the types of sinkholes?
Not all sinkholes are the same, however, even if the overall process — water eroding bedrock — is the same. There are three types of natural sinkholes.
1. Dissolution sinkholes. These sinkholes are the result of there not being much groundcover, like vegetation, over the bedrock. Water slips through pre-existing holes in the bedrock and begins to circulate through the bedrock. A depression in the ground can form, and if the bedrock layers beneath are sturdy enough or there’s enough debris blocking the flow of water, the sinkhole may stop deepening. This could result in the formation of a pond-like areas and even wetlands, according to the USGS.
2. Cover-subsidence sinkholes. These sinkholes start with something permeable covering the sinkhole while also containing a good deal of sand. This sediment begins to spill — or spall as the proper nomenclature refers to it — into those empty caverns among the bedrock. Over time, a depression in the surface may occur. This sediment can block the caverns and prevent the flow of water. These sorts of sinkholes are never very large, according to the Southwest Florida Water Management District, since the sediment prevents the water from further eroding the surrounding bedrock.
3. Cover-collapse sinkholes. Perhaps the most well-known of sinkholes, cover-collapse sinkholes are also the most dramatic. The surface area above the bedrock in this instance is mostly clay, spalls into the cavities. But since the clay is sturdy, arches form as its slowly spalls. This arch continues to support the surface ground until it becomes so thin that it collapses into the cavern below, swallowing up everything above it.
There is one final type of sinkhole, and that’s man-made sinkholes. These sinkholes are the result of a variety of practices, from drilling to mining to changes in water diversion systems to broken pipes.
Can we predict when sinkholes will happen?
While sinkholes have a reputation for being sudden occurrences, they happen over long periods of time. This means there are sometimes signs that a sinkhole could be forming under your feet.
If you’re looking for signs of a sinkhole below a building, the University of Florida recommends being aware of structural cracks in walls and floors, cloudy well water and doors and windows that won’t close properly.
On the ground, there are likely to be more signs, including wilting or dying vegetation, previously buried things — like fence posts, roots or structural foundations — becoming visible, the formation of new and small ponds and slumping trees and fences.
Should a sinkhole occur near you, the Southwest Florida Water Management District recommends evacuating the premises and then notifying your insurance agency and the city.