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.
This steady state condition can be determined by simple lake hydrology. In warm lakes, evaporation may play a significant role in determining the size or level of the lake at steady state. In such cases, one can gain insight into lake dynamics through energy budget analyses . For example, by calculating energy losses and gains from evaporation and radiation, it is possible to estimate the volcanic energy input into a lake. A tunnel was dug to that lake to control the lake level and volume to prevent major disasters.