Lesson 9: Glacial Processes and Landforms Flashcards
4 glacial processes
Erosion
Transportation
Entrainment
Sedimentation/deposition
Define erosion
Weathering of a glacial valley floor and sides by processes of freeze-thaw, weakens the rock, allowing the moving glacier to erode and remove more rock debris, which may be transported over longer distances
3 types of transportation
Supraglacial
Englacial
Subglacial
Define supraglacial
Mainly weathered material carried on top of the ice. Includes material falling from hillsides being washed or blown down, plus atmospheric fallout such as volcanic ash
Define englacial
Formally supraglacial material, but now buried by fresh snow and carried with the ice
Define subglacial
Material carried below the ice. Includes material eroded from the glacier bed and valley walls, material frozen to the base from subglacial streams, as well as englacial material that has worked its way down through the glacier or ice sheet
Define entrainment
Surface sediment is incorporated into a fluid flow (air, ice, water) as part of the process of erosion
Define deposition
Deposition of sediment transported by the ice occurs when it melts - mainly in the ablation zone close to he glaciers snout. Here the sediment in and on the ice melts. Water may then carry the sediment further away from the ice
Define plucking
Freeze thaw weathering with basal melt water
Define abrasion
Rocks being transported scratch bedrock, breaking more rock away from the base and valley walls of the glacier
Define crushing
Direct fracturing of weak bedrock by the weight of the glacier, producing large angular rocks
Define basal melting
Meltwater causes fluvial erosion processes such as abrasion, hydraulic action, attrition and corrosion
Describe cirque glacier
Amphitheatre shaped depression with a steep back wall and rock lip
Process of formation of cirque glacier
Large rounded hollow high on a mountainside is eroded and deepened by plucking and abrasion due to the rotational movement of ice
Example of a cirque glacier
Cwm Idwal, Snowdonia
Describe arete
Narrow, knife-edge ridge between 2 cirques
Process of formation of arete
Plucking and abrasion on the back wall of 2 cirques on a mountainside mean they erode backwards towards one another. Freeze-thaw important
Example of arete
Striding edge, Lake District
Describe pyramidal peak
Pointed mountain peak with 3 or more cirques
Process of formation pyramidal peak
Erosional processes within cirques erode backwards into each other. Plucking important
Example pyramidal peak
Matterhorn, Alps
Describe glacial trough
U-shaped valley with step sides and a wide, flat floor
Process of formation of glacial trough
V-shaped river valley widened and deepened from plucking and abrasion by a valley glacier which goes through the landscape rather than around
Example of glacial trough
Nant Ffrancon Valley, Snowdonia
Describe truncated spur
Steep rocky valley side where spurs of a river valley used to interlock before glaciation
Process of formation of truncated spurs
Valley glaciers less flexible than rivers and remove the ends of interlocking spurs by plucking and abrasion as they move down the river valley
Example of truncated spurs
Mer de Glace, Alps
Describe hanging valley
Small tributary V-shaped or small U-shaped valley high above the main glacial trough floor, often with a waterfall as the river flows over the edge
Process of formation of hanging valley
Thicker glacial ice is the main glacial trough eroded downwards more rapidly than thinner ice or river tributary valleys. The floor of the tributary valleys are left high above the main valley floor
Example of hanging valley
Berwyn Mountains, Wales
Describe ribbon lake
Long, narrow lake along the floor of a glacial trough
Process of formation of ribbon lake
Increased plucking and abrasion by the valley glacier deepen part of the valley floor, causing the confluence of glaciers or weaker rocks
Example of ribbon lake
Llyn Ogwen, Wales
Describe roche moutonnee
Mass of bare rock on the valley floor with a smooth stoss and a steep jagged lee
Process of formation of roche moutonnee
More resistant rock outcrop causes ice movement by creep and regelation. Ice slide over rock, smooths the stoss while refreezing on the lee causes plucking
Example of roche moutonnee
Lembert Dome, Yosemite NP, California
Describe knock and lochan
Lowland areas with alternating small rock hills (knock) and hollows, often containing small lakes (lochan)
Process of formation of knock and lochan
Scouring at the base of the glacier excavates areas of weaker rock, forming hollows of meltwater and precipitation following ice retreat
Example of knock and lochan
Shetland Islands, Scotland
Describe crag and tail
Very large mass of hard rock forms a steep stoss with a gently sloping tail of deposited material
Process of formation of crag and tail
Large mass of hard rock is resistant to ice scouring and creates a steep stoss. Reduced glacier velocity on the lee protects softer rock and allows deposition - sheltering diminishes with distance - sloping tail
Example of crag and tail
Castle Rock, Edinburgh
