The How Sinkholes work.


How do sinkholes work?

Maybe it’s something that you’ve only seen in movies or maybe you’ve read about it in the paper, but when the earth opens up, it can literally swallow anything that gets in its path, whether it’s a house, a car, or an ocean. This phenomenon is not really as rare an occurrence as many people believe and while they don’t happen all the time, they certainly are something that exist and can happen for apparently no reason at all. These gigantic craters in the earth are called sinkholes and they’re not always known for being negative things. While a sinkhole located in the middle of a neighborhood with homes and a community is obviously a negative thing, consider also that the most beautiful natural pools in Mexico were created by sinkholes and now tourists from all over the world visit there to visit the peace and relaxation that those sinkholes created. But how worried should you be that the ground beneath you will just split in two and leave you in an unfortunate situation? Well in truth the odds aren’t likely that you will experience a sinkhole first-hand but knowing things such as which areas are more prone to them than can definitely make you feel more prepared and learning about how the earth below can suddenly break apart, will definitely shake the ground you’re standing on!

Although it may appear as though sinkholes, which are also called sinks, may be seen as just a hole in the ground, they are actually much more than just that. Sinkholes are not usually any larger than 100 feet deep, they can cover small areas that appear to be ponds or they can cover miles and miles of an area. Sinkholes generally occur in areas that are often exposed to water, and more importantly, what kind of rock is underneath the soil, as opposed to the rock that is above the soil, which is called overburden. The rock most usually found in areas where sinkholes have occurred is evaporate or carbonate rock, such as limestone, salt, gypsum, or dolomite.

The reason why sinkholes appear in some areas that are exposed to water and not others is because it’s actually what happens to that water during the process of the sinkhole developing that is the difference as is again, the type of underlying rock. When water has had a great deal of interaction with plants and has absorbed an abundance of carbon dioxide, it becomes acidic. As that acidic water comes into contact with the bedrock, it slowly erodes away small tunnels throughout the rock, creating small passageways for even more water to travel through the rock. These passages are called conduits and they help to eventually create underground basins, which are called recharge areas. These recharge areas have water flowing into them and out of them continuously and this water reaches the subsurface of the earth, or the underlying rock, causing it to dissolve away even faster. If a flood happens to occur in the area of a developing sinkhole, the small conduits can also trap things such as topsoil and other matter, which would further develop the sinkhole as the water then would not be able to move out and would be further trapped inside the sinkhole. Sometimes, when only a small amount of water is responsible for holding up an entire section of earth and that water sees even a slight fall in the level of water, this lack of water can also cause a sinkhole. The United States has a number of areas where sinkholes are quite prominent. Among them are Florida, Alabama, Kentucky, Missouri, Pennsylvania, Tennessee, and Texas.

How Sinkholes Occur Naturally

If you ever get the chance to see one up close, it may look as though the earth’s surface had a great deal to do with the fact that it just opened up and swallowed a car. However, there has been a lot going on underneath that surface for weeks, months, maybe even years before the grand finale event of the earth splitting in two actually happens. This type of sinkhole is known as a cover-collapse sinkhole and it occurs when the overburden becomes too weak to be able to support any of the weight on top of it. With these types of sinkholes, the overburden has usually been formed from soft soil, such as soil that has a lot of clay in it. What happens then is that a cave will form underneath the soil. The overburden will then spill over into the empty space that has been created by the cavern, leaving the area underneath the overburden empty. Over time, the top of the overburden, which is the surface that we see, will collapse into the newly formed cavern underneath it because it has become too thin and weak to support its own weight. This is considered the cover collapse. In some instances, the cover is strong enough to maintain itself but then when a car or something else that has weight to it goes over its surface, it then becomes much too weak and breaks.

Another quieter kind of sinkhole is a cover-subsidence sinkhole. These sinkholes often end up forming ponds because the water just doesn’t have anywhere to go. This type of sinkhole develops when water collects and pushes down and into the soft overburden. Sandy that has clay in it and sits on top of limestone, or other soft rock, is where these sinkholes are most likely to occur and they’re not likely to be very large either. As the limestone is literally washed away by the water, it will create an empty area that will start to become filled in with the overburden. This leaves a concave impression, such as a bowl, in the earth. Once the hole has reached a certain size, sand and sediment will start to flow into the hole and begin to fill it up. Although it won’t become completely filled, this is the reason why these sinkholes are much smaller than the cover-collapse sinkholes. The sand and sediment that flows into the hole will also travel into the small conduits within the soil and will block all exits for the water, which is why is stands still within the sinkhole.

Sometimes cover-subsidence sinkholes are confused with being dissolution or solution sinkholes. In this case, the latter works much like the former in that acidic water touches rock and erodes it to the point where a giant hole is worn away on the surface of the soil. The difference between the two is that with dissolution sinkholes, there is no existence of an overburden and so the soil does not flow back into the hole or cover the rock. However, the water is still trapped within the hole as sand and sediment still fill the small conduits, leaving the water trapped within the sinkhole.

Sinkholes Caused by Humans

It’s not only the unfortunate meeting of water, rock, and soil that causes sinkholes. Often, especially in areas that are highly populated, humans cause sinkholes for many different reasons. Construction often plays a part in creating sinkholes because there is a lot of drilling and vibrating happening on the earth’s surface. When a pipe breaks, this also often plays a part in the development of sinkholes because of the high volume of water on rather weak soil and rock. High car or foot traffic can also wear away at the earth’s surface and cause sinkholes, as can changes in weight, such as the building and development of many new buildings or communities.

The Making of a Sinkhole


 The How Sinkholes work of Sinkholes.

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