Cirques

Cirques are a steep bowl-shaped hollow occurring at the end of a valley glacier by erosion.

   The formation of a cirque

Cirques are found among mountains as a result of alpine glaciers (alpine glaciers form the crests and slopes of a mountain). Cirques may get up to a square kilometer in size usually on the high mountain side near the firn line. The firn line is the ‘line’ where firn (a type of snow that has been left over past seasons that has been recrystallised. It is ice that is the stage between snow and glacial ice) is found at the altitude that it accumulates.

Cirques are surrounded by on three sides by steep cliffs. The highest cliff is called a headwall. The fourth side is called the lip, threshold or sill and is the side which the glacier flowed away from the cirque. Many glacial cirques contain tarns (a mountain lake or pool, formed in a cirque) dammed by either till (debris) or a bedrock threshold. When enough snow accumulates it can flow out the opening of the bowl and form valley glaciers which may be several kilometers long.