A volcanic crater lake, or simply crater lake, is a lake in a crater that was formed by explosive activity or a collapse during a volcanic eruption. Water from various sources accumulates in the crater to form the crater lake.

Formation Lakes in calderas fill large craters formed by the collapse of a volcano during an eruption. Rain, snow and ice melt, and groundwater accumulate in the calderas to form crater lakes. These lakes are often cold, freshwater lakes, but may also be warm and highly acidic, due to hydrothermal nature of their origin.

Lakes in maars (low-profile volcanoes, below the level of the surrounding terrain), fill medium-sized craters where an eruption deposited debris around a vent.

Crater lakes form as the created depression, within the crater rim, is filled by water. The water may come from precipitation, groundwater circulation (often hydrothermal fluids in the case of volcanic craters) or melted ice. Its level rises until an equilibrium is reached between the rates of incoming and outgoing water. Sources of water loss singly or together may include evaporation, subsurface seepage, and, in places, surface leakage or overflow when the lake level reaches the lowest point on its rim. At such a saddle location, the upper portion of the lake is contained only by its adjacent natural volcanic dam; continued leakage through or surface outflow across the dam can erode its included material, thus lowering lake level until a new equilibrium of water flow, erosion, and rock resistance is established. If the volcanic dam portion erodes rapidly or fails catastrophically, the occurrence produces a breakout or outburst flood. With changes in environmental conditions over time, the occurrence of such floods is common to all natural dam types.

These lakes may become soda lakes, many of which are associated with active tectonic and volcanic zones.

Examples

A well-known crater lake, which bears the same name as the geological feature, is Crater Lake in Oregon, United States. It is located in the caldera of Mount Mazama. It is the deepest lake in the United States with a depth of . Crater Lake is fed solely by falling rain and snow, with no inflow or outflow at the surface, and hence is one of the clearest lakes in the world.

Due to their unstable environments, some crater lakes exist only intermittently. Caldera lakes in contrast can be quite large and long-lasting. For instance, Lake Toba in Indonesia formed after its eruption around 75,000 years ago. At around by in extent and deep at its deepest point, Lake Toba is the largest crater lake in the world.

The highest volcano in the world, 6,893-m (22,615-ft) Ojos del Salado in Chile, has a permanent crater lake about in diameter at an elevation of on its eastern side.

Around Mount Gambier in South Australia, there is a cluster of crater lakes, of which Blue Lake / Warwar is the most well known.

Dangers While many crater lakes are picturesque, they can also be deadly. Gas discharges from Lake Nyos in Cameroon suffocated 1,800 people in 1986, and crater lakes such as Mount Ruapehu's in New Zealand often contribute to destructive lahars.

Distinction from other volcanic lakes

Certain bodies of water, although their formation is directly related to volcanic activity, are not usually referred to as crater lakes, including: Lakes created by volcanic dams due to lava flowing outside of the volcanic edifice/caldera, such as Garibaldi Lake in Canada, Fuji Five Lakes in Japan Closed atoll lagoons, such as Clipperton lagoon, whose formation process also implies subsequent biogeomorphologic processes Ponds encountered at the bottom of waterfalls occurring in volcanic canyons in a volcanic context, but not within a volcanic edifice/caldera (such as Trou de Fer on Réunion Island)

List

Africa Lake LocationWaw an Namus (three small salt lakes in the caldera) LibyaDeriba Caldera SudanMeme River Basin lakes (Lake Barombi Koto, Lake Barombi Mbo, Lake Mboandong and Lake Dissoni/Soden) CameroonLake Nachtiga (between Mount Cameroon and the Atlantic coast) CameroonBakossi Mountains: Lake Bermin and Mount Manengouba lakes (lac Mâle and lac Femelle) CameroonAdamawa crater lakes (Tison, Mbalang) CameroonOku Volcanic Field, including Lake Nyos, Lake Oku, Lake Monoun, Mount Mbapit crater lake, Lake Awing and the Bambili lakes CameroonDallol (various acid ponds) EthiopiaZengena LakeEthiopiaEnyo Lake (or Haro Dandii, a lake filling a double crater caldera on Mount Dendi) and Lake Wonchi (Badda Rogghie Mountains) EthiopiaDebre Zeyit crater lakes (Bishoftu, Hora, Bishoftu Guda, Koriftu and seasonal Cheleklaka) EthiopiaLake Dembel, Mount Zuqualla EthiopiaLake Ara Shetan (Butajiri-Silti Volcanic Field) EthiopiaO'a Caldera, with Lake Shala and the smaller Chitu water-filled maar EthiopiaBilate River Volcanic Field (several water-filled maars) EthiopiaEl Sod (small salt lake), Borena Zone EthiopiaMount Biao, Bioko Island Equatorial GuineaLago a Pot, Annobón Island Equatorial GuineaLake Assal DjiboutiKabarole District lakes (including lakes Nyinabulitwa, Nyabikere, Nkuruba, Kifuruka) UgandaMany crater lakes in the Katwe-Kikorongo and Bunyaruguru (or Kichwambe) volcanic fields, respectively on the North and South sides of the Kazinga Channel (including Lake Katwe in the Queen Elizabeth National Park) UgandaMuhavura (small crater lake) Rwanda / UgandaMount Bisoke Rwanda / Democratic Republic of CongoCrocodile Lake, Flamingo Lake, Tilapia Lake, on Central Island (Lake Turkana) KenyaMount Marsabit (at least two lakes) KenyaEmuruangogolak (several maar lakes) KenyaLake Simbi, Mount Homa KenyaLake Sonachi (Crater Lake Game Sanctuary) KenyaLake Chala Kenya / TanzaniaSouthern Highlands crater lakes (Lake Ngozi, Kiungululu Crater, Masoko Crater) TanzaniaLakes Magadi and Empakaai (Ngorongoro Conservation Area) TanzaniaLake Dziani Boundouni, Mohéli Island ComorosDziani Dzaha, Petite-Terre MayotteLake Tritriva MadagascarNosy Be crater lakes MadagascarItasy crater lakes (close to the larger Lake Itasy) MadagascarTrou aux Cerfs MauritiusGanga Talao lake MauritiusBassin Blanc Mauritius Piton de l'Eau RéunionLagoa do Fanal Portugal, MadeiraLaguna de los Ciclos (Charco Verde), El Golfo, Lanzarote Spain, Canary IslandsPedra de Lume (salt lake in the crater), Sal Island Cape VerdeQueen Mary's Peak (heart-shaped crater lake) Tristan da Cunha

Antarctica and the sub-Antarctic islands Lake LocationDeception Island maare Off the Antarctic Peninsula coastMount Larson crater lake, Thule Island South Sandwich IslandsSmall crater lakes on the top of various scoria cones, Marion Island Prince Edward IslandsBassin du Cratère (connected to sea since 1780, now an 'almost crater lake'), Saint-Paul Saint-Paul and Amsterdam IslandsLac bleu, Amsterdam Saint-Paul and Amsterdam IslandsGrand Cratère, Île de la Possession Crozet Islands

Asia