Coulee lakes are also of volcanic origin but they are formed by the flow of lava across the valley of some river so that it blocks the river flow and gives rise to lakes. Lake Tana of Absyssinia is a characteristic example. Several lakes of this type are found in Iceland. Such lakes are usually rectangular in outline but may be irregular also. Sink lakes are characteristic of limestone regions, where the water descending through the shallow holes produces large underground caves. In case of roof of such a subterranean cavern collapses, a basin is formed. Such a basin resembles a sink and has also been formed by the sinking of the land. The lakes formed in these depressions are known as ‘Sink Lakes’. These are usually small in size.
Crater lakes are formed by the impounding of water in the craters of extince volcanoes. These lakes have a circular outline and are surrounded by deep walls of lava. Usually Crater Lakes are very deep and their depth is the greatest near the centre. The Crater Lake of Oregon and the Caldera of Roman Campagana are some of the most outstanding lakes of this type. Such lakes are also found in the Avergne District of France and the Eifle region of Germany.
Salines lakes are the salt water lakes of arid and desert regions. These are not so short-lived as the playas and are more permanent. They have a more constant water supply but are bitter in taste because of the lack of an outlet. But these may also disappear leaving behind a ‘salt-Pan’. The best case in point is the 4000 square miles saline Lake Eyre, which lies in the ‘Dead Heart’ of Australia.