Volcanic Lake / Crater Lake
A volcanic lake or crater lake forms in a crater or caldera or depression left by a volcanic eruption. Crater or volcanic lakes can form in the craters of active volcanoes. Fumarole activity can make the lake highly acidic,hot and a deep green colour.
Gases can be trapped in the water, in 1986 1800 people were killed when gas escaped from the volcanic lake at Lake Nyos,Cameroon. If no fumarolic activity is present then Volcanic Lakes can be be very pure.
Calderas can hold enormous lakes , Crater Lake is 594m deep the deepest lake in the USA. The crater lake on New Zealands White Island is one of the most acidic lakes in the world.