Sinkholes Explained

Sinkholes have recently been all over the news. The dangerous phenomena swallows cars, homes, and buildings whole. But what are sinkholes, how do they form, and is there anything you can do to prevent them?

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According to the U.S. Geological Survey, sinkholes are pits in the ground that form in areas where water gathers without external drainage. As the water does drain from the area, it erodes the top layer of rock. Once the rock is completely eroded, the surface collapses. Most of the time, it takes many, many years for a sink hole to be created. However, the ones you hear about on the news are rapid and sudden.

There are 3 types of sinkholes. The first type of sinkhole is a dissolution or solution. In this type of sinkhole, there is a small layer of vegetation over a layer of rock (normally limestone or bedrock). Water from the soil slowly trickles down to the layer of rock causing it to gradually depress. Many dissolution sinkholes become ponds, as debris lines the indented rock and traps the water.

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The second type of sinkhole is a cover-subsidence sinkhole. This sinkhole happens when there is sand on top of bedrock. The sand will gradually fill in the openings of the rock which causes it to sink. This filtration slowly causes the size of the depression to increase.

The last type of sinkhole, and the most dangerous, is cover-collapse sinkhole. With cover-collapse sinkholes, bedrock is covered by clay. Underneath these layers, water is dissolving and eroding ground sediments, creating a cavern. This cavern will continue to form as ground continues to erode, leaving a thing layer at the top. Eventually, the top layer collapses taking anything on top of it with it.


Unfortunately, there is not much you can do to prevent sinkholes. However, there are warning signs. The most obvious sign is seeing the ground beginning to slump. This will also cause surrounding trees or fences to lean. Next, if there is a structure on top of a imminent sink hole, one can begin to observe cracks. The windows and doors may also begin to be difficult to shut as the structure of the building has most likely shifted.