Image courtesy of U.S. Geological Survey via Flickr
Hundreds of campers had to be evacuated from an Australian beach in September 2015 when the ground opened up beneath them and began to swallow entire campsites. The sinkhole quickly grew to the size of a football field, taking vehicles and and tents into its depths.
This sinkhole is not the first of it’s kind, nor will it be the last; in 2014 it was reported that almost 300 sinkholes had opened in Florida in a span of four years, and the number continues to rise.
Sinkholes are naturally occurring phenomena that come up in the news every so often when the earth opens up suddenly, terrifying unsuspecting people and causing catastrophic damages.
Why Sinkholes Form
A sinkhole is a bowl-shaped depression created by the formation of underground cavities, which cause the land to collapse upon itself and drain into the void. Some may take many years to form, while others can occur abruptly.
Sinkholes often occur as the result of karst processes, in which soluble rock, like limestone or gypsum, is eroded underground by acidic water. When the rock can no longer hold the weight of the above layer, the land above collapses into the cavity.
There are three different types of sinkholes:
- Dissolution sinkholes:Rainfall and surface water gradually dissolve and carry away bedrock by percolating through tiny crevices within, creating a depression.
- Cover-subsidence sinkholes:These kinds of sinkholes occur over long periods of time in areas where bedrock is covered by sand. Sand gradually trickles down into holes in the rock, causing the surface to sink.
- Cover-collapse sinkholes:Cover-collapse sinkholes are the ones seen on the news, and can be catastrophic. These sinkholes occur in situations when the bedrock is covered by a layer of clay, which erodes underground into cavities within the rock, as depicted below.
Can Sinkholes Be Prevented?
Exactly where and when a sinkhole will occur generally cannot be predicted. While it can be said that some areas, like those with limestone, are more prone to the development of sinkholes, they often happen without any warning.
States in the eastern U.S., especially Florida, are susceptible to sinkhole formation due to the presence of limestone and regular rainfall. Karst areas occur all over the world and can be seen in Mexico, China, and Italy, among other countries.
Along with natural factors, human activities can also play a part in sinkhole growth.
Excessive groundwater pumping can offset the pressure systems within underground aquifers, causing the soil above to fall through. Sinkholes can also form as a result of construction, which can force runoff into concentrated areas, instead of dispersing by soaking into the ground.
Leaning trees, cracks in building foundation, skewed door frames can all be indicators of an oncoming collapse, but sometimes, the ground collapses with no warning at all.