Erosional features of glacier and underground water

Glacier

• Cirque (corrie): armchair-shaped hollow at the head of a glacier, made by plucking and abrasion; a lake in it is a tarn.
• Arête: knife-edge ridge between two cirques.
• Horn (pyramidal peak): sharp peak left when cirques cut back on all sides, e.g. Matterhorn.
• U-shaped valley (glacial trough): the glacier widens and deepens a river valley.
• Hanging valley: side valley left high above the main trough; it often ends in a waterfall.
• Fjord: glacial trough drowned by the sea.
• Roche moutonnée, striations and grooves: smoothed and scratched bedrock surfaces.
• Rock basins and tarns.

Underground water

Groundwater erodes mostly by solution, working on soluble rocks (limestone, dolomite, gypsum). The landscape is called karst topography. Features:

• Sinkholes (dolines): closed depressions made by dissolution or by collapse of a cave roof.
• Caves and caverns: underground hollows enlarged along joints and bedding planes.
• Sinking streams and underground rivers, springs.
• Lapies (karren): grooves and ridges on exposed limestone.
• Uvala and polje: large, compound sinkholes and wide valley-like basins.
• Natural bridges and dry valleys.