Look at the geographical map and see the lakes on all continents. Some of them are elongated, others are rounded. Some are located in mountainous areas, others – on vast flat plains, some very deep, and there are very small, drying up. The shape and depth of the lakes depends on the size of the basin – the recess that they occupy. And lake basins are formed in different ways.
In areas composed of limestone, dolomite and gypsum, karst lake basins arise as a result of the chemical dissolution of these rocks by surface and groundwater. Thickness of sand and clay, lying above karst rocks, fall into underground cavities, forming hollows on the earth’s surface. Over time, they are filled with water and become lakes. Karst lakes are also found in caves, they can be seen in the Crimea, the Caucasus, the Urals and other areas.
The crater of the lake can become a crater or caldera of an extinct volcano, and sometimes a drop on the surface of a frozen lava flow. Such lakes are found on the Kuril and Japanese islands, on Kamchatka, on the island of Java and in other volcanic regions of the Earth. It happens that lava and debris of igneous rocks block the valley of the river, in this case a volcanic lake also appears.
These lakes fill the hollows created by the glacier. Moving, he plowed out a softer soil, there were depressions. In some places – long and narrow, and in others – oval. Over time, the lows filled with water – glacier lakes appeared. There are many such lakes in the north of the North American continent, in Eurasia on the Scandinavian and Kola Peninsulas, on Taimyr. In mountainous areas, glacial lakes are located in the bowl-shaped depressions of the upper parts of the slopes, they were created by small mountain glaciers.
So called lakes, located in large troughs of the earth’s crust. Lakes can fill and deep tectonic cracks – rifts (Lake Baikal, Tanganyika). Most of the world’s large lakes are tectonic in origin.