Mikkeli Hiidenkirnu, Mikkeli, Finnland #
Cavities or holes which appear to have been drilled in rocks by eddying currents bearing stones, gravel or morainic debris, are called giant's kettles, giant's cauldrons or potholes. If a surface is covered by a glacier, the water which is produced by the thawing of ice and snow can flow down a crevasse as a swirling cascade or moulin. As the water works its way downwards it can abrade the sides of the crevasse and sometimes of the bed of the glacier too, and forms smooth regular potholes. After the ice leaves the area, giant's cauldrons are seen as an empty shaft, or as a pipe filled with gravel, sand or boulders.