A thermokarst depression with relatively steep sides and a flat floor, which may be occupied by a lake. Alases are well developed in Siberia (the word ‘alas’ is of Yakutian origin) where they can occupy 40–50% of the land surface.
Geography
In a periglacial landscape, a large, steep-sided, flat-bottomed depression which can be several kilometres across. Lakes often occur in alases, which may then develop into pingos.