8 markers on the formation of landforms

Question 1

How are Corries formed?

Answer 1

• Development starts with nivation of a small hollow in which snow collects and accumulates year on year.
• Over time these hollows enlarge and contain more snow which eventually compresses into glacier ice.
• As the ice acquires weight and depth, it begins to move, creating rotational flow that is the result of the ice’s internal stresses. This rotational movement causes plucking of the back wall, making it increasingly steep.
• Abrasion also occurs through the process of rotational scouring, as the ice and debris move against the back wall, abrading and smoothing the surface. The debris derived from plucking and weathering above the hollow falls into the bergschrund or crevasse which abuts the back wall, helping to abrade the hollow and causing it to deepen. Over time, this enlarges the hollow further. The debris also causes the development of rock lips or thresholds at the front of the hollow.

Question 2

Aretes

Answer 2

Erosional landform. Narrow steep-sided ridge found between two corries. Ridge is often so narrow that it is described as knife-edged. Eg Striding Edge in the Lake District which has steep slopes either side that are 200-300m high and almost vertical in some places. Describe formation of a corrie.

Question 3

Pyramidal peak

Answer 3

Erosional Landform. Where three or more corries develop around a hill or mountain top and their back walls retreat, the remaining mass will be itself steepened to form a pyramidal peak. Weathering of the peak may further sharpen its shape. The Matterhorn in the Swiss Alps is over 1200m high. Describe formation of a corrie.

Question 4

Troughs

Answer 4

• Erosional landform. Glaciers flow down pre-existing river valleys under gravity. As they move they erode the sides and floor of the valley causing the shape to become deeper, wider and straighter.
• The mass of ice has far more erosive power than the river that originally cut the valley. They are rather parabolic in shape partly due to the weathering and mass movement of the upper part of the valley sides that goes on both during the glacial period and in the subsequent periglacial period as the glacier retreats.
• The resultant scree slopes that accumulate at the base of the valley sides lessen the slope angle. There are often variations in the long profile of glacial troughs. When compressing flow occurs the valley is over-deepened to form rock basins and rock steps.
• This process may be particularly evident where there are alternating bands of rock of different resistances on the valley floor - the weaker rock being eroded more rapidly to form the basins

Question 5

Roche Moutonees and Striations

Answer 5

• Roche moutonnées are formed through the processes of plucking, abrasion, and pressure melting.
• As advancing ice passes over them there is localised pressure melting on the up-valley side
• The area is smoothed and streamlined by abrasion and often has striations. On the down-valley side pressure is reduced and meltwater re-freezes resulting in plucking and steepening.

Question 6

Terminal moraine