Frazil ice <1mm thick
Sea water freezes at –1.8°C, forming tiny crystals that calm the surface of the water.
They grow into tiny platelets and spikes, then interlace to become frazil ice.
Pancake ice 1–10cm thick
Frazil ice collects into tiny floes, which bond together in pans. The pans bump against each other, forming a sheet of discs with raised edges like pancakes.
Pack ice 1–10m thick
Pancake ice coalesces into pack ice, whose area varies seasonally. Even in winter, wind and currents maintain open areas of water called polynyas.
Fast ice 1–2m thick
Along coastal margins and in protected bays, areas of mostly permanent floating ‘fast’ ice provide a bridge between pack ice and land. It easily supports vehicles.