How do sinkholes form? What are the famous sinkholes in China
Sinkhole refers to a huge volume, steep and trapped rock wall, deep well or barrel profile and other extraordinary spatial and morphological characteristics, developed in the soluble rock layer with a particularly large thickness and a particularly deep groundwater level, from the underground to the surface, the average width and depth are greater than 100 meters, and the bottom is connected to the underground river.
Sinkhole is a special geological landscape distributed in karst areas, which is caused by the ground erosion or the collapse of the top of the underground cave. There are two causes of sinkholes, most of which are collapse type and the rare one is erosion type.
How do sinkholes form?
The formation of a sinkhole requires at least six simultaneous conditions:
One is that the limestone layer must be thick. Only a thick enough rock layer can provide enough space for a sinkhole to form.
Second, the water level of the underground river should be very deep.
Third, the thickness of the vadose zone should be large.
Fourth, the rainfall must be large, so that the flow and momentum of the underground river is large enough to wash away the fallen stones.
Fifth, the rock layer should be flat. Looking at the cliffs around the sinkhole, you will find that the rock layers are parallel to the ground, just like the layers of SLATE piled around, and only such rock layers can collapse.
Sixth, the crust should protrude. The movement of the earth's crust provides the power for the rock layers to collapse.
The famous sinkhole in China
Xiaozhai Sinkhole
Located 91 kilometers away from Fengjie County Jingzhu Township village. Tiankeng is called "karst funnel landform" in geography. The ground elevation of the mouth of Xiaozhai Tiankeng is 1331 meters, the depth is 666.2 meters, the diameter of the mouth is 622 meters, and the diameter of the bottom is 522 meters.
The sides of the pit are steep, and a path leads to the bottom of the pit on the northeast side of the cliff. The pit wall has two levels of platform: located at a depth of 300 meters, the first level of platform, 2-10 meters wide, there are two houses on the platform, people used to live in seclusion; The other level of platform is located at a depth of 400 meters, in the shape of a slope, the slope of vegetation, wildflowers in full bloom, the pit wall has several suspended springs flying down the bottom of the pit. There is an underground river at the bottom of the tunnel, and Xiaozhai Tiankeng is a "skylight" of the underground river.
Xiaozhai Tiankeng and Tianjing Gorge Gorge belong to the same karst system. The underground river water at the bottom of Tiankeng is supplied by Tianjing Gorge Gorge and discharged from Maze Gorge. The underground channel from Tiankeng to the exit of Labyrinth Gorge is about 4 kilometers long. Xiaozhai Tiankeng, known as "the first pit under heaven", is one of the wonders of caves in the world today.
Sichuan Tiankeng
Since September 2012, a bottomless "sinkhole" with a diameter of about 20 meters appeared in a corn field of Group 6, Sanzhi Village, Gongnong Town, Lizhou District, Guangyuan. According to nearby villagers, the "sinkhole" was formed after six days and six nights of collapse, but the cause of formation is not clear.
The "sinkhole" is about 20 metres in diameter, and the deepest part of the hole where the mud layer can be seen is about 15 metres. In order to test the depth of the pit, someone picked up a stone weighing about 2 kilograms and threw it into the pit, only to hear "snap, snap, snap..." The sound continues and diminishes.
"The stone did not get to the bottom, and the 'crack' sound it made was that it hit other stones in the pit. It is impossible to estimate how deep the pit is."
Tiankeng in Jiangsu province
On January 5, 2014, a road under construction in Binhe New Town, Xinpu District, Lianyungang City, suddenly collapsed, and a huge "sinkhole" was formed, forcing the road construction to stop. The reporter learned that the "sinkhole" is located in a phosphate mine on the side of the road, about 70 meters away from the new road, and the new road has a 500-meter section through the "goaf" of the phosphate mine.
After the incident, the phosphate mine immediately reported to a number of relevant departments and took effective preventive measures. At present, solutions for the disposal of "sinkholes" and the next step of road safety are being further demonstrated. The picture shows the "sinkhole" more than 100 meters in diameter.