Pressure ridge (ice)
A pressure ridge is an ice formation typically found on large frozen lakes or sea ice during the winter. In the most basic sense, a pressure ridge is a long crack in the ice that occurs because of repeated heating and cooling on the surface of the lake.
In cases of extreme cold, ice will shrink in volume like any other solid, opening up cracks in the surface of lakes that are completely frozen over. The cracks quickly fill with water and freeze again, but when the temperature rises later, the ice expands and forces itself upward along the lines of the crack, in much the same fashion that plate tectonics creates mountain ranges, albeit on a much smaller scale. Pressure ridges can sometimes extend for miles, making an ice road impassable for truckers hauling freight to far northern locations.
Pressure ridges also develop on lava flows when the solid colder top layer is deformed by movements of the underflowing hotter lava.
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