Crater Lake, Oregon.
A crater lake is an accumulation of water, usually by precipitation of rain or snow but sometimes ground water, in a volcanic crater (caldera). Should an eruption occur, the resulting mudflow (lahar) is often more destructive than a lava flow owing to its greater speed. A noted example is Crater Lake, in Crater Lake Park, Oregon. The waters of the lake were formed by precipitation and are maintained solely by rain and snow; there is no outlet.