“Sinkholes: an act of Geology, not God”

As I was brainstorming a topic for this blog post, I came across the picture above. The image is that of a giant sinkhole that destroyed several homes in Guatemala City in 2007. The scale of the image in the sinkhole was simply breathtaking—and it encouraged me to explore the topic further. At first, the image of these sinkholes almost looks unreal; they really attest to the power of water via erosion.

Sinkholes are underground caverns—of various sizes—that are carved out by water or heavy rains which are naturally acidic. They can be found all over the world; however, they are most common in places where the ground is made of soft rocks like gypsum, limestone, or salt beds. These rocks are easily dissolved (soluble rock), thus creating giant caverns. This type of ground can also be referred to as “Karst Terrain.” After a bit of research, I learned that –according to the USGS–roughly 20 percent of the world’s surface comprised of karst topographies. Just about every state contains at least some Karst Terrain; Florida, for instance is almost completely underlain by limestone. Nevertheless, this process of erosion takes place over long periods of time—100s, 1000s, 10,000s of years.

There are two main ‘methods’ by which sinkholes form. The first option is a divot forming in the ground as a result of the gradual erosion of the earth beneath it. The second— more catastrophic— option involves a lag time between the erosion process and the collapse of the top group layer; this lag time results in the top layer remaining intact while a huge cavern is carved out underneath. These are the sinkholes that initially caught my eye —- they seem so unrealistic!

There are also other types of sinkholes in addition to Karst sinkholes. For instance, man induced sinkholes in urban areas due to the presence of pipelines, water mains, and sewer lines – which are basically manmade caves underground. As the aging infrastructure deteriorates, there is a heightened potential for collapse.

The USGS is mapping the geology of areas in order to determine where the soluble rocks are on the surface and sub-surface in order to help assess risk for sink holes.

At a first glance, this kind of risk assessment did not seem very vital—however, I stand much corrected as these incidents are much more common than I initially thought. In Tampa, Florida, a man was killed as a sinkhole overcame his home. The gaping hole was 9 meters across and 15 meters deep! Similarly, a 150-metre by 50-metre sinkhole in Ningxiang, China destroyed at least 20 houses in June 2010—fortunately, no one was killed in this incident. Another incident occurred at a subway construction site in central Guangzhou, China. Interestingly, a “2008 report by the Guangdong Geology Institute found the surrounding area was not geologically stable, though plans for two subway lines passing through the area still proceeded” (Sinkholes: An Act of Geology”).

For more interesting information about sinkholes, see the articles below 🙂

Sources Consulted

“Sinkholes: An Act of Geology, Not God.” South China Morning Post.Web. 12 Mar. 2013. .

“What Causes A Sinkhole.” Business Insider. Web. 12 Mar. 2013. .