Tiankeng refers to a super-large karst negative landform with extraordinary spatial features such as huge volume, steep rock wall, subsidence, deep well or barrel outline, etc. It is developed in a soluble rock stratum with extremely huge thickness and extremely deep groundwater level, with an average width and depth from underground to ground exceeding 100 m, and its bottom is connected with an underground river (or there is evidence that the underground river has moved). Recently, "subsidence" has occurred frequently, especially in Yibin area, where 26 large pits appeared in 7 days. What is the reason? Zhang Ke believes that if the collapse is concentrated, it is often caused by human factors. For example, pumping groundwater makes underground caves form negative pressure, which accelerates the process of collapse. "The collapse of Changning in Yibin, Sichuan Province is likely to be related to the pumping of groundwater from nearby coal mines, which is a man-made geological disaster. The collapse on the Quzhou Expressway in Zhejiang Province may be caused by the collapse of the original cave under the expressway. " Zhang can analyze. In addition, in the valley area, if the groundwater flow is accelerated or excessively pumped, the soil will collapse under the influence of water level change and gravity. This may be the case in Xinchang Town, Dayi, and huaiyuan town, Chongzhou. According to reports, huaiyuan town in Chongzhou has also carried out seismic exploration and measurement, blasting and other operations to generate artificial sources. The blasting caused the gravel layer to collapse loosely under the action of groundwater. So it is also a man-made geological disaster. The collapse of Ganjiang Road in Nanchang may be because the road was built on loose layers such as floodplain. In addition, the recent collapse in China is relatively concentrated, which may also be related to more rainfall. As for the sinking of Guatemala, Zhang Ke thinks that there have been many landslides in this area. This year's landslide may be related to tropical storms and heavy rains. It is difficult to regard the rumor that an earthquake will occur after "subsidence" as an earthquake precursor. Zhang can't agree with this. He said: "If the subsidence is related to tectonic movements such as earthquakes, its distribution should be highly directional and should occur at the same time or after the earthquake. Especially after the earthquake, heavy rain will cause a lot of collapses. However, according to the information I have, it seems extremely rare for collapse to be a precursor to earthquakes. " Jie Yi introduced that when building a house, you can drain water in advance to let the ground sink, and then build a house on the sinking ground, thus avoiding "ground sinking". Guangzhou residents don't have to worry about this problem, because Guangzhou's underground is granite, and removing the weathered layer foundation will be very stable. Expert interpretation: the sink is different from the sinkhole. According to the definition of the paper "On Karst Tiankeng" by geologist Zhu, a sinkhole is a pit-like negative terrain developed in carbonate rocks, which leads from underground to the ground and is surrounded by steep rock walls. The depth and plane width (mouth or bottom) range from 100 meters to hundreds of meters, and the bottom is connected with an underground river during its development period. In Jie Yi's view, what has appeared frequently in various places recently should actually be called "subsidence". He said: "Strictly speaking, subsidence and sinkhole are not the same concept. Subsidence is ground collapse, and tiankeng is a proper name of karst landform. "