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What Is a Sinkhole and What Causes Them?

Sinkholes are some of the most fascinating disasters to occur, and they happen all across the world. In certain areas of the United States, sinkholes are common occurrences. Typically, in Southern states like Texas, Alabama, Kentucky, Tennessee, and Florida, sinkholes can become a problem. Sinkholes aren’t just natural disasters, either, as they can happen as a result of man-made causes.

Natural Sinkholes

Naturally occurring sinkholes happen because underground water supplies erode the structure of the land. Over long periods of time, sinkholes begin to develop right underneath us, without anyone noticing until they appear in a dramatic fashion.

The earth beneath our roads and buildings is comprised of soil and rocks, which can be loose or compacted. Over many years, underground water and runoff water pools in the land and works its way into the crevices between sediment and rocks. Occasionally, floods and storm water drainage will cause the water flow to increase and flush out underground support structures. When the underground structure cannot bear the weight of above surface area any longer, it begins to collapse. A sinkhole opens up.

Man-Made Sinkholes

Manmade sinkholes can also occur, resulting from a combination of ongoing building and poor infrastructure. Construction activities like drilling, mining, and blasting significantly weaken the underground natural support of the earth. Often times, improper planning during construction can lead to broken pipes, causing water to spill out and work its way into the soil. If soil is not adequately compacted, the water has the same effect as it does with natural sinkholes. It begins to eat away at the crevices between soil and rocks, widening these gaps gradually until the structure is compromised.

There are three main types of sinkholes:

  • Solution sinkholes – This type of sinkhole is most likely to occur in areas with weak or thin topsoil. Because the soil isn’t thick enough to protect the underlying bedrock from erosion, water can more easily make its way into the foundation and cause a deep depression in the land. These sinkholes normally develop gradually and are not as drastic, although this is not always the case.
  • Collapse sinkhole – The most dramatic kind of sinkhole, collapsing sinkholes start out gradual and tend to go unnoticed. The ground is covered in a thick layer of topsoil, so people don’t realize the structure below is being severely eroded and giant cracks are beginning to form. Eventually, the bedrock becomes so cracked and weak that it completely gives out, creating a large collapse in the ground above. Once a collapsed sinkhole begins to open up, it can rapidly get worse and often expands within minutes.
  • Cover subsidence sinkhole – These sinkholes are gradual and are the result of topsoil that is not well compacted. These usually occur in areas where the topsoil is made of loose clay or sandy-type dirt. Over time, bedrock begins to erode and the loose topsoil falls into the cracks, widening them and increasing erosion rates. As the soil settles in these cracks, it causes a surface dent in the topsoil, but does not open a hole underneath.
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