This cavern was located on the main lava stream coming from Tolbachik volcano in Kamchatka. The mouth of the cavern was about 20 feet in diameter and the heat was intense. If you could stand the heat and peep over the edge you could see a river of lava flowing within. I took a few photographs but was careful not to fry my camera.
There were some smaller lava vents dotted around where you could peer into the depths and see the bright red lava flowing. These vents were surrounded by deposits of iridescent colours – emerald green, turquoise, orange, yellow from the gasses hissing out. I would love to know what these deposits are. I will post a question to some geologists and see what they have to say.