A vocabulary of landscape — a landscape of words
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pack ice
Pack ice is sea ice that is floating free and moving with the wind and current, as against fast-ice, which is frozen to the shore and does not move. It is described by how much of the surface it covers, from open pack that a ship can work through to close pack where the floes are touching and very close pack where they are frozen together. It rafts, ridges, opens into leads, and closes again without warning.
Etymology
The word came into English from Dutch, from whaling and from Arctic voyaging in the seventeenth century, and it uses pack in the sense of a mass of things crowded together. English took most of its sea-ice vocabulary the same way, from Dutch, Danish, Norwegian, Russian, and Inuktitut.
Notes
The classic hazard is not the ice itself but the closing. A vessel working a lead can be caught when the wind shifts and the floes come together, and the pressure of a large field converging is enough to lift or crush a hull, which is what happened to Shackleton’s Endurance. Floe, lead, polynya, nilas, and pressure ridge name the parts of it.