This is happening in some Russian forests, people are finding these deep holes in dense forests & places where its not possible for trucks or any other instrument or device that could be used to drill them.
"They appear in the dense forest, in the places you can't get on the car or truck to bring any device to drill the ground. There is no any soil that should be taken from such deep holes is found.
There are no any reasonable ideas on how these holes appear and what they are being used for.
The theory is that these holes were formed by larva burning away the trees and leaving behind ashes which were eroded away. This theory is problematic.
These holes appear in remote forests where its very hard to bring in equipment to dig them.