Unstable Earth – What Causes Sinkholes?

What Causes Sinkholes?
Sinkholes seem to come out of nowhere, and can be found throughout the world. They appear in all sorts of strange places: the backyards of homeowners, on busy roadways, and even the North Lawn of the White House. What causes sinkholes, and what are the warning signs that one might be developing?

Despite their seemingly sudden appearance, there’s actually nothing quick about sinkholes at all. Here’s an explanation behind this geological phenomenon.

What Causes Sinkholes?

Sinkholes can be found all over the world, and they go by many different names which are often used interchangeably; cenote, sink, sink-hole, swallet, swallow hole, and doline are a few examples.

In the United States, sinkholes are particularly common in Florida, Alabama, Tennessee, Texas, Missouri, Pennsylvania, and Kentucky.

The causes of sinkholes can be broken down into two broad categories: natural or man-made.

Natural Sinkholes

Naturally-occurring sinkholes can be attributed to erosion or the presence of underground water.

The ground underneath your feet isn’t as solid as you think. It’s comprised of dirt, rocks, and minerals that are continuously loosened as water seeps its way down to underground water reservoirs.

This process slowly erodes the rocks and minerals packed within the dirt, sometimes weakening its structure significantly. When the ground can no longer support the earth’s surface, it then collapses and opens up a sinkhole.

Rainwater passing through decaying plant debris can also be to blame, since this acidic water can further erode these materials.

Man-made Sinkholes

It’s not just mother nature that causes sinkholes. Construction, mining, drilling, and other excavation practices compromise the structure of dirt, furthering corrosion and causing sinkholes to form.

The same can be said for broken water and drain pipes. The excessive amount of water that passes through rocks, minerals, and dirt can cause it to erode quickly, resulting in the formation of a sinkhole.

Heavy traffic can also result in a sinkhole, with mass amounts of vehicles or heavy machinery putting too much pressure on the earth’s surface and causing a collapse.

Different Types of Sinkholes

There are three main types of sinkholes: solution sinkholes, cover collapse sinkholes, and cover subsidence sinkholes.

  • Solution: You’ll most often see these sinkholes in areas that have a very thin layer of soil covering the surface. This exposes the layer of bedrock below, making it vulnerable to water erosion. As water erodes the bedrock, it begins to carry away small pieces of rock until a small depression forms. A sinkhole will then form.
  • Cover Collapse: In contrast, these types of sinkholes take place when the bedrock is deep below the surface and covered by a significant layer of soil. As the bedrock erodes, cracks will begin to form in the rocky areas surrounding it. This significantly weakens its structure until the bedrock can no longer support surface weight. This can cause a collapse to occur suddenly, creating a massive hole in just minutes.
  • Cover Subsidence: These kinds of holes form over a period of time. Unlike the sudden collapse of Solution and Cover Collapse sinkholes, the bedrock in these areas is covered by soil and materials that are not well-formed to begin with. As erosion occurs, this material begins to filter through the cracks and settle into its crevices, eventually creating a well-formed cavity.

Sinkhole Warning Signs

Warning signs of a sinkhole normally appear during the final stages. Keep an eye out for impending disaster by looking for the following signs on your property:

  • New cracks in your foundation, interior walls, or ground outside
  • Depressions in the ground
  • Doors or windows that are suddenly difficult to open or close
  • Trees or fences that appear to be tilting or fall down completely  
  • A hole in the ground that appears suddenly

As mentioned before, sinkholes very rarely appear all of a sudden. They are the result of underground erosion that takes place over time, though away from view. Hopefully by knowing their causes, you’ll be able to keep your property (and yourself) safe from their “sudden” appearance.

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