Cirque

A cirque is an amphitheater shaped valley carved by glacial erosion, open on one side and enclosed by steep, cliff-like slopes on three or more of its other sides, also known by the Scottish Gaelic derived name corrie or the Welsh word cwm. Ice and glacial debris converging down these steep slopes from several directions typically overdeepen the cirque floor below the level of its outlet, so that once the ice has melted the floor often holds a small mountain lake called a tarn, dammed by a rim of moraine, till or bedrock. Similarly shaped basins can also form through fluvial rather than glacial erosion, when an intermittent river cuts down through limestone or chalk in a karst landscape, leaving comparable sheer walled cirques known as makhtesh.