permafrost

 Ground that remains frozen continuously for two or more years — soil, rock, and sediment held together by ice. Permafrost underlies roughly a quarter of the Northern Hemisphere's land surface and can extend to depths of over a thousand feet. It is not permanent despite its name. As the Arctic warms, permafrost is thawing — releasing stored carbon, destabilizing infrastructure, and reshaping landscapes into the pitted, slumping terrain called thermokarst.