What is a pressure ridge?
A pressure ridge develops in an ice cover as a result of a stress regime established within the plane of the ice. Within sea ice expanses, pressure ridges originate from the interaction between floes, as they collide with each other. Currents and winds are the main driving forces, but the latter is particularly effective when they have a predominant direction. Pressure ridges are made up of angular ice blocks of various sizes that pile up on the floes. The part of the ridge that is above the water surface is known as the sail; that below it as the keel.
One of the largest pressure ridges on record had a sail extending 12 metres (39 ft) above the water surface and a keel depth of 45 metres (148 ft). The total thickness for a multiyear ridge was reported to be 40 metres (130 ft).