Volcanic lakes occur in volcanic areas young and old, in both active and extinct volcanoes. A disturbance of the drainage pattern will lead to an accumulation of water in low areas, with or without a surface outlet. Many crater lakes lack an outlet and only lose water through evaporation or subsurface leakage.
Most volcanic lakes receive an input of hydrothermal or volcanic fluids.
In exceptional cases, lakes may be intruded by new magma and volcanic explosions can occur in or below the lake. Some volcanic lakes are fed by the effluents of surface hot springs or fumarolic vents. In high areas, lakes of glacial origin may become volcanic lakes through activity and inputs of nearby volcanoes. Volcanic lakes range in composition from common meteoric waters to those with a strong volcanic imprint , and temperatures can vary from ambient to close to boiling. Some subglacial lakes can be warmer than ice and have no direct contact with the atmosphere.