Formation of distinctive landform predominantly influenced by deposition

Question 1

Formation of terminal moraines

Answer 1

Terminal moraines are a ridge of till extending across a glacial trough - they are usually steeper on the up-valley side and tend to be crescent shaped, reaching further down-valley in the centre
- these landforms mark the position of the maximum advance of the ice and were deposited at the glacier snout; their crescent shape is due to the position of the snout, as further advance occurs in the centre of the glacier, as there is no friction with the valley sides

The steeper up-valley side is the result of the ice behind supporting the deposits and making them less likely to collapse

Question 2

Formation of lateral moraines

Answer 2

Lateral moraines are a ridge of till running along the edge of the glacial valley - the material accumulates on top of the glacier having been weathered from the exposed valley sides
- as the glacier melts or retreats, this material sinks through the ice to the ground and deposited

Question 3

Formation of a recessional moraine

Answer 3

Recessional moraines are a series of ridges running transversely across glacial troughs and which are broadly parallel to each other and to the terminal moraine
- they are found further up the valley than the terminal moraine, and form during a temporary stand-still in retreat

These temporary pauses are rarely prolonged, and therefore recessional moraines seldom exceed 100 metres in height

Question 4

Formation of erratics

Answer 4

An erratic is an individual piece of rock, varying in size from a small pebble to a large boulder - these are composed of a different geology from that of the area in which they have been deposited

They were eroded, most likely by plucking, or added to the supra-glacial debris by weathering and rockfall, in an area of one type of geology and then transported and deposited into an area with differing rock type

Question 5

The formation of a drumlin

Answer 5

A drumlin is a mound of glacial debris that has been streamlined into an elongated hill, and are often a prominent landform, sometimes more than a kilometres in length and 100 metres high

In plan they are typically pear-shaped and aligned in the direction of ice flow - the higher and wider blunt end faces the ice flow, while the lee side is more gently tapered

Their formation isn’t fully understood, however they may be formed by:
1. Lodgement of subglacial debris as it melts out of the basal ice layers
2. Reshaping of previously deposited material during a subsequent re-advance
3. Accumulation of material around a bedrock obstruction - these are known as rock-cored drumlins
4. Thinning of ice as it spreads out over a lowland area, reducing its ability to carry debris

Question 6

Formation of a till sheet

Answer 6

A till sheet is formed when a large mass of unstratified drift is deposited at the end of a period of ice sheet advance, which smooths the underlying surface
- the till itself is variable in composition, depending greatly on the nature of the rocks over which the ice has moved
- if there is high clay content, compaction by weight of the overlying ice sheet may lead to relatively hard deposits