What are the phenomenon (artificial and natural) in play in this photograph "350m beneath Berezniki in Russia"?
As stated in the caption for the picture this is an inside view of a potash mine.

Mining professionals regard potash, like most coal, to be a soft rock; unlike hard rock such as most metal sulfides.

With hard rock mining, the rock is mined by drilling holes and using explosives to break up the rock. The rock is then loaded and transported out of the mine.

Most soft rock mines, and particularly potash mines, do not use drilling and blasting as the main means of removing rock. Instead they use specialized cutting machines to cut the rock. The shapes left in the rock, in the picture are marks created by the cutting heads of such machines. Usage of such a machine can be seen at the 3:30 mark in this You Tube video.

I answered the question What would you call this mining vehicle? (Ural-20R, used in mining) on SE Engineering two years ago, when someone asked about the purpose of an unusual mining machine.

Such machines are typically called continuous miners.