What are sinkholes and how are they caused?

We always hear about them, whether they appear in Mexico, China or Japan, but what exactly causes the creation of those mysterious gaping holes in the earth?

Photo by: AFP
Photo by: AFP

A giant sinkhole, measuring about 20 by 15 metres, appeared in the middle of a five-lane urban boulevard in Fukuoka, southwestern Japan, on November 8, 2016. There were no injuries reported.

Updated Nov 9, 2016

A sinkhole is a hole in the ground formed by erosion and the drainage of water. The holes can sometimes measure at just a few feet, or they may even be large enough to swallow entire structures.


The giant hole in Japan exposed support columns of nearby buildings at a traffic intersection, alarming locals of the possibility of further collapses. Fukuoka's transport bureau said the ongoing extension of a nearby subway line could be linked to the creation of the sinkhole. Fukuoka, Japan, November 8, 2016. Reuters/archive

But the real question is, what are the causes of these sinkholes that we hear about on the news all the time? Let’s take a look at some facts about these gigantic openings in the earth.


Sinkholes are often the result of natural processes, however they can also be man-made. Natural sinkholes take place due to erosion or underground water. They start forming long before they actually appear. Guilin, China, January 7, 2015. Image: Reuters/archive


The ground is made of dirt, along with many rocks and minerals. Water continually seeps through these, as it makes its way to the ground water reservoirs. As this occurs, the water gradually erodes the rocks and minerals. Wuzhou,China, August 14, 2014. Image: Reuters/archive


Sometimes, the water flow washes away the underground structure of the land. And when the structure becomes too weak to support the surface of the earth, it collapses and a hole is opened. And, this is how sinkholes are formed. Beijing, February 16, 2014. Image: Reuters/archive


Humans also play a role in the formation of sinkholes. Activities like drilling, mining, broken water or drain pipes, construction, or even heavy traffic can result in small to large sinkholes. Shaanxi, China, July 27, 2013. Image: Reuters/archive


Water seeping from broken pipes can permeate mud and rocks and erode the ground underneath and cause sinkholes. Occasionally, heavy weight on soft soil can cause the ground to collapse, resulting in a sinkhole. Ohio, US, July 3, 2013. Image: Reuters/archive


Areas that have a bedrock made up of limestone, salt deposits or carbonate rock are much more likely to erode and are more susceptible to the formation of such holes. Solikamsk, Russia, November 20, 2014. Image: AA/archive

What are the different types of sinkholes?

There are 3 main types of sinkholes: Solution, Cover Collapse and Cover Subsidence.


Solution sinkholes are most frequently seen in areas that have a very thin cover of soil on the surface, exposing the solid foundation below to continuous erosion by water. As the water seeps through the foundation, it carries away small pieces of rock with it. Sometimes, the foundation may collapse all of a sudden or over a gradual process. Nata, Brazil, June 22, 2014. Image: AP/archive


Cover-collapse sinkholes appear suddenly and form large holes very quickly. These are the types that usually make headlines. They occur a deep layer of soil and earth is present between the surface and bedrock, solid rock underneath the earth’s surface. Clermont, US, August 12, 2013. Image: AP/archive


When the bedrock begins eroding, many weak points begin to form in the layers of soil and rock above it. Finally, the weak points become a large hole within the bedrock that can not support the weight above it. Beijing, China, April 26, 2011. Image: AFP.


Cover-subsidence sinkholes are formed slowly over time. This occurs when the bedrock is covered by soil and materials that are not joined closely. Winter Park, Florida, US, May 11, 1981. Image: AP/archive


When the bedrock begins eroding, the clay or sand starts flowing through the cracks and settles into the spaces left behind. Over time, this forms a hole on the surface of the soil and not under it. Oklahoma, US, April 6, 2008. Image: AP/archive

 

Source: 
TRTWorld and agencies