Glacial Erosional Landforms Flashcards
What is a cirque?
Armchair shaped hollow in a mountainside with a steep backwall and a rock lip.
How is a cirque formed?
A large rounded hollow high on a mountainside is eroded and deepened by plucking (at the backwall) and abrasion due to the rotational ice movement
What is an example of a cirque?
Cwm Idwal, Snowdonia
What is an arete?
A narrow, knife-edged ridge between two cirques
How is an arete formed?
Plucking and abrasion on the backwall of each cirque mean they erode backwards towards one another
What is an example of an arete?
Striding Edge, Lake District
What is a pyramidal peak?
A pointed mountain with three or more cirques
How is a pyramidal peak formed?
The erosional processes (mainly plucking) such as plucking within multiple nearby cirques mean they erode backwards towards each other to create a sharp pointed mountain
What is an example of a pyramidal peak?
Mount Everest, Himalayas
What is a U-shaped valley?
A valley with steep sides and a wide, flat floor
How is a U-shaped valley formed?
A V-shaped river valley is widened and deepened by plucking/abrasion by a glacier which goes through the landscape rather than around it
What is an example of a U-shaped valley?
Nant Ffrancon Valley, Snowdonia
What is a truncated spur?
Very steep, almost vertical valley sides where interlocking spurs of a river valley once were
How is a truncated spur formed?
Valley glaciers remove the ends of interlocking spurs through plucking and abrasion as they move down the valley
What is an example of a truncated spur?
Truncated spurs in the Nant Ffrancon Valley
What is a hanging valley?
Small tributary valleys high above the main U-shaped valley floor, often with a waterfall.
How is a hanging valley formed?
Powerful, thicker glacial ice in the main U-shaped valley is widened and deepened more rapidly than tributaries with thin ice or rivers, leaving these tributaries at a much higher altitude than the U-shaped valley floor
What is an example of a hanging valley?
Yosemite Falls, USA
What is a ribbon lake?
A long narrow lake along the floor of a U-shaped valley
How is a ribbon lake formed?
Areas of increased plucking/abrasion below the glacier deepen the valley floor, leaving a depression which fills with water after the glacier melts
What is an example of a ribbon lake?
Llyn Ogwen, Snowdonia
What is a roche moutonnee?
A mass of bare rock on the valley floor with a smooth stoss (up-valley) side and a jagged lee (down-valley) side
How is a roche moutonnee formed?
High pressure ice on the stoss side causes regelation of ice (melting under high pressure) which smoothens the up-valley side but plucks the lee side due to refreezing of ice under lower pressure, creating a jagged cliff
What is an example of a roche moutonnee?
Roche moutonnee on the Nant Ffrancon valley floor
What is a knock and lochan landscape?
A lowland area with alternating small rock hills (knock) and hollows which often contain small lakes (lochan)
How is a knock and lochan landscape formed?
Scouring (abrasion) of weaker rock forms hollows which are filled with water when a glacier melts
What is an example of a knock and lochan landscape?
East Shetland Islands
What is a crag and tail?
A very large mass of hard rock which forms a steep stoss (up-valley side) with a gently sloping tail of deposited material
How is a crag and tail formed?
A steep stoss is created due to the hard rock’s ice resistance while reduced glacier velocity on the lee protects softer rock and allows deposition. The sheltering effect is reduced with distance so a sloped tail is formed
What is an example of a crag and tail?
Edinburgh Castle, Scotland
