A volcanic crater lake is a lake in a crater that was formed from explosive activity or collapse during a volcanic eruption. Lakes in calderas fill large craters formed by the collapse of a volcano during an eruption. Lakes in maars 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 fromprecipitation, groundwater circulation 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. A well-known crater lake, which bears the same name as the geological feature, is Crater Lake in Oregon. 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. The highest volcano in the world, 6,893-m Ojos del Salado in Chile, has a permanent crater lake about in diameter at an elevation of on its eastern side. This is most likely the highest lake of any kind 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 formed after its eruption around 75,000 years ago. At around 100 km by 30 km in extent and 505 m deep at its deepest point, Lake Toba is the largest crater lake in the world. While many crater lakes are picturesque, they can also be deadly. Gas discharges from Lake Nyos in suffocated 1,800 people in 1986, and crater lakes such as Mount Ruapehu's often contribute to destructive lahars. 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
