The sea ice surrounding a crack becomes reduced in thickness approaching the center of the crack and field teams have to be vigilant when approaching a sea ice crack. Ice drills are used to determine the thickness of the sea ice surrounding a crack if a crack is questionable for supporting the passage of tracked vehicles. Sea ice cracks form due to forces working on the sea ice sheet. Ice sheets move in response to current and wind and they rise and fall with tidal rhythms. Deposition of snow by wind builds up pressure on the sea ice surface.
Waves move into shallow water, increase in height and cause stress in the overlying ice sheet.
Where the ice sheet comes in contact with an island or shoreline, sea ice cracks and pressure ridges will be evident. When a fast moving ice sheet comes into contact with a slow moving or stationary ice sheet, a pileup of ice blocks of angular shapes may form. Sea ice cracks are an inevitable result. Here is a tidal pressure ridge at the Cape Evans shoreline with the Royal Society Range in the background across McMurdo Sound. Pressure ridges or blocks may jut up from these shoreline cracks.