There have been quite a few sinkholes appearing lately; therefore, I thought it would be of interest to some of you what causes them and what the warning signs are.
A sinkhole appears when what is immediately below the surface shifts somewhere else. Some sinkholes cause a slight depression on the ground, whereas some reach down half a kilometer.
Sinkholes can swallow streets, houses, cars, and even an entire building. Should they appear in the wilderness, they can result in lakes, pits, or even tourist attractions, like Belize’s Great Blue Hole.
One of the world’s deepest sinkholes is situated in Chongquig, China, and it is about 662 meters deep.
How do these gaping gullets form in the Earth? Is it possible to foresee them?
Since there is no natural surface drainage, the water in the sinkhole drains downwards into subsurface layers. Three main causes create sinkholes. Firstly the rocks below the surface are made out of materials that dissolve in water easily, such as limestone or gypsum.
The second cause is the rocks under the surface consisting of small grains that can be carried away by underground water currents. Last but not least, water movements above-ground such as intense rainstorms, floods, long-term leakage from sewers, or storm-water pipes can cause sinkholes.
Sinkholes usually form in areas with limestone. That too in areas that are tropical and have a moist climate. They usually don’t form in dry climates, which is why we don’t see many sinkholes forming in Australia. Tropical environments create rapid sinkholes. Sinkholes also come into existence because of mining activity.
Some of the world-famous sinkholes are the Guatemala sinkhole, the sinkhole that appeared in a backyard in Queensland, the sinkhole on a bustling Japanese street, and the one that appeared near Prime Minister Malcolm Turnbull’s house.
While sinkholes have a reputation for suddenly occurring, they actually happen over long periods. This means there can be signs that a sinkhole could be forming right under your feet.
The last stage is when a hole or basin is formed on the very surface. Signs such as fresh cracks in the foundations of houses and buildings, cracks in interior walls and the ground outside, depressions in the ground, tilted or fallen fences and trees, and the sudden appearance of a hole in the ground indicate that you’re dealing with a sinkhole.
The most dangerous of sinkholes is a cover-collapse sinkhole, a layer of clay covers the bedrock. Under this is water which dissolves an underground cavern, so gradually, the ground sediments begin to erode into the cavern from the bottom.
‘Dragon Hole’ appears to be the world’s deepest underwater sinkhole, which is found in the South China Sea. According to researchers who have explored the site say that it’s 987 feet (300 meters) deep.
More than 20 species of fish have been found in the upper part of the sinkhole, known as a blue hole. Below 100 meters, it is unlikely to have and life there as it is mostly oxygen-free. A “blue hole” is a colossal sinkhole or cave system in the ocean which is visible from the surface.
Where are the 3 types of natural sinkholes:
Solution sinkholes – occurs in areas where limestone is exposed on the surface or is coved by a thin layer of sand. Such as not having much groundcover.
Cover-subsidence sinkholes – These sorts of sinkholes are not very large.
Cover-collapse sinkholes – These are generally very abrupt and can be dramatic.
Sinkholes may form gradually or suddenly and found worldwide.