I've mailed about sinkholes before--it's one of the things that I think that you will be interested in--but this sinkhole in Russia, near the town of Solikamsk, makes other sinkholes look more like a pothole.
It emerged as a respectable 40m-diameter sinkhole. 10 months later it has tripled in size, swallowing a number of unoccupied holiday homes in the process. It now threatens to begin swallowing trees from the forest.
There is extensive mining in the area, and the sinkhole is reckoned to have begun after a mineshaft became flooded, causing erosion from below.
The nearest politician says, essentially, “There is no problem”.
--------- Alex Kemp