How does sinkhole form?

You might have come across news of ground or road caving in during tunnelling work or after heavy rains. You might have even seen one in your neighbourhood. It is frightening to imagine the ground beneath your feet collapsing and leaving a gaping hole in the ground. Unfortunately, it is a common occurrence world over. So, what is a sinkhole and how does it form?

Sinkholes are cavities in the ground caused by collapse of the surface layer. They may appear suddenly and have devastating consequences. (Sinkholes swallowing buildings. cars on the road and even houses have regularly made news. In January 2020, at least six people were killed and 16 injured after an enormous sinkhole swallowed a bus and a number of pedestrians in central China.)

What causes sinkholes?

Sinkholes are caused by erosion of underlying rock layer. When minerals below the surface of the ground gradually dissolve, say in rainwater, the ground above collapses forming the sinkhole. According to the National Geographic Channel, there is another type of sinkhole – the one that forms when the roof of a cave collapses and exposes the underground cavern.

Sinkholes are most common in karst terrain. These are regions where the rock below the land surface can naturally be dissolved by groundwater circulating through it. Soluble rocks include salt beds and domes, gypsum, and limestone and other carbonate rock. Some sinkholes form when the land surface is changed, such as when industrial and runoff-storage ponds are created.

But these scary phenomena have become a lot more common today as a result of human activity. Construction of roads, buildings and other structures, deep mining, fracking and over-pumping of groundwater affect the structural integrity of underlying rock. Such activities may cause water to collect in certain areas and wash away the supporting rock layer (especially at low sea levels and after heavy rains). Scientists also attribute the recent rise in number of sinkholes to climate change, which has led to heavier rainfall.

Warning signs

The final collapse of the surface might take days, hours or even seconds. But there are some warning signs. These include doors and windows failing to dose properly, cracks appearing in the foundation of houses and a circular pattern of ground cracks outlining the sinking area. In some cases, ground movement can be detected.

 

Picture Credit : Google

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