freeze-up

The autumn process by which a river, lake, or sea gradually freezes over — beginning with shore ice, building through slush and pancake ice, and finally locking into a solid surface. In the Arctic and subarctic, freeze-up marks the transition from one mode of travel (boats) to another (sleds, snowmobiles, walking). The period between open water and solid ice — when the surface is neither navigable nor walkable — is one of the most dangerous and isolating times of the year.