Ice, Drifting of

the movement of ice on rivers and lakes caused by the action of the current or wind. Drifting of ice occurs in the spring and fall. In the spring, drifting of ice cakes created by the breakup of ice cover occurs, whereas in the fall there is drifting of ice cakes resulting from the freezing together of mush ice, frazil ice, puddle, and broken-off shore ice. On many rivers the movement of ice in the fall is preceded by the movement of frazil ice. Frequently the movement of ice on rivers is accompanied by ice jams. The density of the drifting ice is rated on a numbered scale: a ten-point system is used on rivers and a three-point scale on lakes.