Pressure ridge

A pressure ridge is an ice formation typically found on large frozen lakes or sea ice during the winter.

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  A long ridge of ice that has formed when two floes of thick ice have been squeezed together by wind or ocean currents, with the ice breaking into chunks that pile upward and also downward below the ice. This ice is difficult to cross on foot or with sleds or snowmobiles.
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  Winter sea ice terrain of the Beaufort Sea - Alaska, North Slope
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  Pressure ridge at Cape Murchison
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  Pressure ridge in Antarctica with Mount Erebus, in the background
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  Pressure ridge on the Ross Sea
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  Pressure ridges on Ross Island as seen from the sea ice near New Zealand's Scott Base.
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  Pressure ridges on Ross Island, Antarctica as seen from the sea ice near New Zealand's Scott Base, looking out towards Mt. Erebus