SINKHOLE- THE HINDU
Six people were killed and 10 are believed to be missing after a bus and some pedestrians were swallowed by a sinkhole in China’s Xining city, the capital of Qinghai province, on Monday (January 13).
• The footage of the incident shared by the state media shows people disappearing as the sinkhole spread, followed by an explosion inside the hole.
• Sinkholes depressions that open up on the ground — are not uncommon in China. In December 2019, a road in southern China’s Guangdong province collapsed, swallowing a cleaning truck and an electric bike.
• In November 2019, Xinhua Net reported the discovery of a giant cluster of sinkholes in south China’s Guangxi Zhuang Autonomous Region.
• Before this, in 2016, scientists discovered the world’s largest cluster of sinkholes in Shaanxi province in Northwest China.
How are sinkholes formed?
• Sinkholes are depressions formed in the ground when layers of the Earth’s surface start collapsing into caverns.
• They can occur suddenly and without warning, because the land under the surface of the Earth can stay intact for a period of time until the spaces get too big.
• Their formation can be caused due to natural processes or human activity. Typically, sinkholes form in areas of “karst” terrains, where the rock below the surface of the Earth can be easily dissolved by groundwater.
• Essentially, this means that when rainwater seeps into the ground, the rock below the surface of the Earth starts dissolving, leading to the creation of spaces.
• This process is a slow and gradual one and can sometimes take hundreds or thousands of years.
• Such terrains are most commonly found in areas with limestone, gypsum or carbonate rocks, as per NASA. The formation of karst terrains is dependent on geology and climate.
• On the other hand, sinkholes can also be formed due to human activity.
• According to the British Geological Survey, this can happen due to broken land drains, water mains and sewerage pipes, increased rainfall, storm events, underlying limestone and diverted surface water, among other reasons.
• There have been many well-documented occurrences of sinkholes forming beneath broken water mains, unlined storm-water culverts and leaking swimming pools/
Sinkholes in China and around the world:
• In China, the mining of coal, zinc, lead and iron ore deposits in karst areas have been associated with the formation of sinkholes due to human activity, according to a 1997 paper published in the journal Environmental Geology.
• In Florida, in an area that is classified as a karst landscape, insurance agencies must provide homeowners coverage against damage that can accrue from ground cover collapse.