A landform that results when ground ice (ice-rich Permafrost is frozen ground that remains at or below zero degrees Celsius (32 degrees Fahrenheit) for two or more years. It forms in regions where the mean annual temperature is... More) melts. The melting leaves small, marshy hollows and hummocks in the land as the ground settles unevenly. See also A (usually shallow) body of water found in a depression within a thermokarst landform. The water is from thawed permafrost. If the permafrost continues to thaw the lake may drain away, leaving a... More.