What is a sinkhole?
A sinkhole is a depression or hole in the ground caused by the structural collapse of the ground’s surface layer. They can also be called a "shake hole," a "denote," a "swallow hole" or a "doline." They can appear gradually or very suddenly, and can vary in size from a few feet wide to hundreds of miles wide and deep. Sinkholes can look like a soil-lined bowl or a gaping chasm edged with bedrock. The largest known sinkholes are Sima Humboldt and Sima Martel in Venezuela, with Humboldt measuring 352m wide and 502m deep.
Why are we talking about them now?
Last night a massive sinkhole opened up on a street in St Albans—20m wide and 10m deep. Several families in the area had to be evacuated overnight. Reports of sinkholes appear to have increased lately: five days ago a 150 metre long and 50 metre wide sinkhole opened up on a campsite in Queensland, Australia, while in August a sinkhole swallowed 5 commuters at a bus stop in China. In 2014 Dr Tony Cooper of the British Geological Survey warned that the number of expected sinkholes in the UK was set to increase. Cooper believes that the number increases when the weather brings high rainfall and oversaturates the ground, so it remains to be seen whether this winter will bring heavy rain and more sinkholes with it.
What causes them?
Sinkholes can be natural or man made. The natural ones occur due to erosion caused by underground water. When water continually seeps through minerals, rocks and mud towards ground reservoirs, it erodes the material. Once that flow of water increases due to rainfall, the underground structure supporting the surface is washed away. The structure becomes too weak to support the ground, so it collapses and a hole opens up. Humans can also cause them through activities like drilling, mining, construction, broken pipes or improperly compacted soil. The heavy weight on soft soil can cause the ground to collapse and open up a sinkhole.
How can I avoid them?
Sinkholes are more common in some places than others. They are infamous in Florida, which gets so many because its underground rock is a soluble substance called "Karst," made up of a variety of soluble rocks. Some 20 per cent of the US consists of this particular type of terrain, so avoid Texas, Alabama, Missouri, Kentucky, Tennessee and Pennsylvania as well. In the UK, some parts of the country are more susceptible than others. Gypsum—a soft sulphate material—is particularly vulnerable to being rapidly eroded. A sinkhole which opened up in Yorkshire in 2014 contained gypsum under its surface. But because humans can cause sinkholes too, their appearance is very difficult to predict. Sometimes a noise can be heard before they appear, and very small holes can occur before the ground opens up. Checking with local authorities to determine what type of terrain your property is located on is the best way to avoid waking up at the bottom of a 10m hole in the morning.
