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Lakes often occur in glacial regions as a result of ponding caused by deposits of till or fluvial material, the melting of ice blocks (kettle lakes), or erosional depressions or rock basins (example, cirque lakes). Because the melting ice provides considerable run off, much of the abraded material can be transported and deposited, often in these lakes. The material is usually somewhat sorted to sorted and stratified. Clay, silt, sand, and gravel can be deposited. In some lakes, alternating light (silt and sand) and dark layers (clay) occur as different erosional environments (possibly summer and winter) supplied varying clastic material. Such deposits are called varved clays. Any filled lake may become buried below the surface. In modern geologic literature, glacio-lacustrine deposition is considered as part of Glacio-Lacustrine deposition because of the gradual transition and great similarities between the two.
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