A Caldera is a vast Cirque-shaped basin of volcanic origin, often with steep walls and a more or less flat bottom. This decrease in terrain is formed on a volcano after the collapse of the crater walls or as a result of its catastrophic eruption.
Golovnino volcano is an active volcano on the island of Kunashir, the southernmost volcano of the Kuril Islands. The last eruption was in 1998. A Caldera up to 4.7 km in diameter is surrounded by a ridge up to 541 m high. At the bottom of the Caldera, 4 small volcanic domes and 2 explosive craters, one of which contains two lakes, they emit jets of gases, thick steam and hot water to the surface. One of them is named hot, and the second, which is located directly in one of the craters-Boiling lake. In lakes there is a large amount of sulfur and sulfide compounds, and on the Boiling and does float sulfide-sulfur foam. You can only get here through the Kurilsky nature reserve.