A crater lake is a lake that forms in a volcanic crater or caldera,such as a maar; less commonly and with lower association to the term a lake may form in an impact crater caused by a meteorite.Sometimes lakes which form inside calderas are called caldera lakes,but often this distinction is not made.Crater lakes covering active (fumarolic) volcanic vents are sometimes known as volcanic lakes,and the water within them is often acidic,saturated with volcanic gases,and cloudy with a strong greenish color.Lakes located in dormant or extinct volcanoes tend to have fresh water,and the water clarity in such lakes can be exceptional due to the lack of inflowing streams and sediment.
A well-known crater lake,which bears the same name as the geological feature,is Crater Lake in Oregon,USA.It is located in the caldera of Mount Mazama,hence the name "Crater Lake" is something of a misnomer.It is the deepest lake in the United States with a depth of 594 m (1,949 ft).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.[1]
The highest volcano in the world,6,893 metres (22,615 ft) Ojos del Salado,has a permanent crater lake about 100 metres (300 ft) in diameter at an elevation of 6,390 m (20,960 ft) on its eastern side.[2] This is most likely the highest lake of any kind in the world.
Due to their unstable environment,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 70,000 years ago and has an area of over 1,000 square kilometres.