Glaciation Terms Flashcards
Freeze-thaw (mechanical weathering)
On exposed rocks water gets into cracks sand as temperature drop below freezing at night the water freezes and expands putting pressure on the rock and forcing it apart and pieces to break off.
Abrasion
Erosion caused by the mechanical action of rocks and boulders in the glacier scraping against the rocks.
Plucking
Erosion where melt water in the glacier freezes against the rock and as the ice moves it pulls (plucks) pieces of the rock away with it.
Rotational slip
Ice in a corrie moves in a circular motion due to gravity. It deepens the hollow into a bowl shape.
Corrie
An armchair shaped hollow in the mountains formed by glacial erosion, rotational slip and freeze-thaw weathering. It is where the valley glacier begins and often contains a lake called a tarn after glaciation.
Arête
A sharp, knife like ridge formed between two corries.
Pyramidal peak
Where several corries cut back to meet at a central point, the mountain takes the form of a steep pyramid.
Glacial trough
A river valley widened and deepened by the erosive action of glaciers; it becomes U shaped rather than V shaped.
Bulldozing
Ice pushes material off all shapes and sizes in front of it as it moves.
Hanging valley
A tributary valley to the main glacier which was not eroded as much as the lower valley and today often has a waterfall well above the valley floor.
Truncated spur
A former river valley spur which has been sliced off by a valley glacier, forming cliff-like edges.
Ribbon lake
A long narrow lake found in glaciated valleys formed in areas where the glacier had more erosive power.
Moraine
Rocks which have been transported and deposited by a glacier some distance from their source region.
Outwash
Material, mainly sand and gravel, deposited by meltwater streams in front of and underneath the glacier. It has been sorted and rounded by water action.
Till
An unsorted mixture of sand, clay and boulders carried by a glacier and deposited as ground moraine over a large area.
