Erosional and depositional landforms of glaciers

A glacier is a large mass of ice formed by compaction and recrystallisation of snow, which moves slowly downslope under its own weight. Types: valley (alpine) glaciers, as in the Nepal Himalaya, and continental ice sheets.

Erosional landforms

Glaciers erode by plucking (ice freezes to the rock and pulls out blocks) and abrasion (rock fragments in the ice scrape the bed).

• 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.

Depositional landforms

Material carried by ice is called till (unsorted, unstratified clay, sand, pebbles and boulders). Features:

• Moraines: lateral, medial, terminal (end) and ground moraines.
• Erratics: large boulders carried far from their source rock.
• Drumlins: smooth, elongated hills of till, shaped like an inverted spoon.
• Eskers: long, winding ridges of sand and gravel left by streams under the ice.
• Kames and outwash plains: mounds and flat areas of sorted sand and gravel built by meltwater.
• Kettle holes: depressions left where buried ice blocks melted.

  Section of a glaciated valley
  \   /\        /\   arete   /
   \_/  \______/  \_ cirque /
        U-shaped valley floor