A kettle is a depression or basin in the glacial drift formed by the ablation (melting) of a mass of glacial ice which was wholly or partly buried. These forms may have any shape in plan, although most tend to be somewhat circular, and vary in depth from less than 8 meters to greater than 45 meters. A kettle may be partially or completely filled with silt and clay (varved clay).
Not all depressions or basins in glaciated areas are kettles. Basins or depressions may also form as a result of irregularly deposited moraines. Other basins, which are not kettles, may be formed by the blocking of a pre-existing valley, differential thawing of perennially frozen ground, and subsidence in bodies of silt.