Massive mystery holes appear in Siberian tundra — and could be linked to climate change
https://edition.cnn.com/2020/09/04/world/craters-tundra-siberia-trnd-scn/index.html
Underground space is widely used by human beings like getting crude oil, piping, building subways, and building underground shops.
But, they are just small portions of earth's underground space. Most of them are still unknown. So, it would be difficult to learn what happened to the holes.
