Glacial landforms

Question 1

What is a corrie? and How are they formed?

Answer 1

Armchair shaped hollows found on upland hills. Steep back wall, on over deepens basin + often a lip at the front. They vary in size + shape.

1. starts w nivation of small hollow on hillside -> snow collects + accumulates yr on yr -> glacial ice
2. These hollows enlarge as abrasion occurs deepening hollow
3. At critical depth, ice acquires rotational movement under its own weight -> enlarges hollow further
4. plucking of back wall = increasingly steep + retreats due to freeze thaw weathering
5. meltwater + debris deprived from plucking + weathering falls into crevasse which abuts the back wall.
6. abrasion continues + meltwater freezes
7. The thinner ice at the front is unable to erode so rapidly so lip is left
8. In post glacial landscape, corrie may become filled w tarn

eg Walcott corrie in Antarctica

Question 2

what is an arête and how are they formed?

Answer 2

Narrow, steep sided ridge found between two corries.
eg striding edge

Glacial erosion, w the steepening of slopes + the retreat of corries that are back to back or alongside each other eg striding edge lake district

Question 3

What is a pyramidal peak?

Answer 3

Where three or more corries develop around a hill and their back walls retreat. eg Matterhorn in Swiss alps

Question 4

How do glacial troughs form?

Answer 4

Glaciers flow down river valleys under gravity, as move they erode sides + floor = shape to deepen, widen + straighten. Mass of ice has more erosive power than river. Parabolic due to weathering + mass movement of the upper part of the valley sides. Scree slopes accumulate at the base of the valley sides, lessen the slope angle.
eg Glee Avon

Question 5

What is a Roche moutonnee? and how are they formed?

Answer 5

A mass of resist rock which has a smooth, rounded up valley slope facing direction of ice flow + down slope formed by plucking

1. glacier reaches resistant obstacle
2. Pressure builds upon stoss side, as ice piles up/ compresses
3. PMP is exceeded
4. Ice flows around the obstacle smoothing by abrasion. Striations may be present too.
5. on lee side Reduction in pressure, decreased temp, refreezes, plucking

Question 6

What are striations?

Answer 6

Scratches + grooves made by debris embedded in the base of the glacier

Question 7

What is a ribbon lakes?

Answer 7

Long + thin lake that collects from meltwater (water after glacier melted) eg Buttermere

Question 8

What is terminal, lateral + recessional moraine?

Answer 8

terminal : Ridge of till extending across a glacial trough.

• steeper on upvalley side
• Mark the position of max. advance of ice + were deposited at the snout
• Crescent shape

lateral: Ridge of till running along edge of glacial valley. Accumulates at top of a glacier having been weathered from exposed valley sides, as the glacier melts or retreats this material sinks through the ice to the ground + is deposited

recessional: Series of ridges (unsorted) running transversely across glacial trough + are broadly parallel to each other + terminal moraine
- found further up valley than terminal moraine
- from during a standstill retreat -> warming

Question 9

What is an erratic? and how do they form?

Answer 9

An individual piece of rock, varying in size from small pebble to large boulder
- composed of different geology than that has been deposited

Eroded most likely by plucking or added to supra-glacial debris by weathering + rockfall in an area of one type of geology + then transported + deposits into an area of different rock type
eg silurian shale deposited on carboniferous limestone a robber in the Yorkshire dales

Question 10

what are drumlins and what are different theories for how they are formed?

Answer 10

Mound of glacial debris that has been streamlined into an elongated hills eg hills of elslack

Cavity fill model: meltwater erosion from floods eg jokulhaulp (cavities in underside of ice) the water erodes giant drumlin shaped scours in the base of the ice, which are infilled with sediment.

Bed deformation model: sediments of the bed are weak so they may deform due to stress of overlying ice, the till may vary in strength so the stiffer parts will deform less -> overlying ice creates mounds of deposition as the glacier streamlines the material as moves over to create streamlined hill.

1. as glacier meets moraine, it travels over it. it doesn’t entrain it as it does not have enough energy + cant around the resistant rock on stoss end
2. as moves over it smooths material down the lee end
3. it ends facing the direction where the ice was going

Question 11

How are till sheets formed?

Answer 11

Large mass of unstratified drift is deposited at the end of a period of ice sheet advances, which smooths the underlying surface till which is variable in composition -> compaction by weight of overlying ice sheet may = hard depositing eg Laurentide