Topic 2 - EQ3 - Glaciation

Question 1

How have subaerial processes contributed to the development of glacial landscapes?

Answer 1

Subaerial freeze thaw (e.g. freeze thaw weathering of a pyramidal peak produces steep weathered features of the landform)

Mass movement (e.g. vital in forming ice contact depositional features such as medial, recessional, terminal and lateral moraines. Weathered material from freeze thaw weathering moves down onto the side of the glacier via mass movement processes, such as rockfall, this then forms distinctive lateral moraine)

Question 2

Explain the formaction of landforms by ice sheet scouring

Answer 2

1 - Roche Moutonnee. As ice moves over stoss side of outcrop it abrades the surface creating a smooth surface with some striations. Reduced pressure on the downward side leads to freezing of meltwater in cracks and plucking creating a jagged lee.

2 - Crag and tail. Formed when a glacier is moving through a landscape eroding less resistant rock, when it reaches a resistant rock outcrop it moves over the resistant rock without eroding, it then deposits on the lee side due to reduced pressure creating a gently sloping downward side of deposited material.

Question 3

Explain the importance of glacial erosion when working out provenance of ice

Answer 3

• Crag and tail (lee is where ice came over second)
• Roche moutonee (smooth side is upward)
• Striations parallel to ice movement
• Corrie orientation (lip points to direction of ice)

Question 4

Explain the importance of glacial deposition when working out former ice mass extent and movement

Answer 4

Extent

• Drumlins (form englacially so bigger swarm = more ice)
• Terminal moraine (ridge of deposited moraine across shows maximum extent of glacier)

Movement

• Drumlins (greater elongation ratio = faster movement, short side is upward, longer is downwards)
• Erratics (determining rock source of erratic shows where ice came from and rough ice direction, e.g. rock from Alisa Craig in Lancashire 200 miles south)

Question 5

Name two ice contact depositional features

Answer 5

• Lateral moraine

- Medial moraine

Question 6

Explain the formation of two ice contact depositional features?

Answer 6

• Lateral moraines are formed when exposed rock on the valley side is weathered and fragments fall down on to the edge of the glacier. This is then carried along the valley and deposited when the ice melts. Lateral moraines form parallel to ice flow.
• Medial moraines are formed when two glaciers meet and the lateral moraines are joined together. When ice melts it deposits this material as unsorted angular moraine can material in the middle of the valley.

Question 7

Explain how depositional landforms can be used to reconstruct ice movement

Answer 7

• Erratics (source of rock shows source of ice movement, e.g. Alisa Craig rock ended up in Lancashire plains)
• Drumlin (greater elongation ratio shows faster movement, crest line indicates direction, shorter upward side where ice came from. E.g. Drumlins of western Scotland)

Question 8

Explain the role of glacial meltwater in creating distinctive landforms

Answer 8

• Glacial meltwater is key in creating outwash plains, flat expanses of fluvio glacial debris in front of the glacier’s snout. As meltwater leaves the snout and reaches the lowland area it loses its energy and deposits its debris load. The heaviest debris is deposited first (e.g. coarse gravel) and the lightest debris deposited last, furthest from the snout. This process is known as imbrication. Therefore, meltwater is instrumental in the formation of outwash plains.
• Meltwater is also key in the formation of meltwater channels (as suggested in the name), meltwater channels are channels cut into bedrock or deposits by the ice margin. Meltwater can erode channels, sometimes even as deep as gorges, as a result of the high hydrostatic pressure within the glacier and their high sediment load. The braiding of proglacial meltwater channels due to variations in meltwater volume between summer and winter. Channels are bigger within glacier due to hydrostatic pressure, channels are often smaller pro-glacially. Meltwater is therefore vital in the formation of meltwater channels.

Question 9

Explain the formation of two ice contact fluvio glacial features

Answer 9

Eskers: ridges of fluvio-glacial sand and debris formed as glacier retreats. Subglacial meltwater streams carry lots of debris due to the high hydrostatic pressure, as the glacier retreats the hydrostatic pressure is released, as a result the streams deposit debris at a constant rate in a long narrow ridge forming an esker

Kame terraces: pressure from the valley sides and the glacier leads to the formation of ice marginal lakes and channels. As water carrying sediment flows into the valley it collects here and meltwater is deposited as ice marginal bodies of water aren’t flowing. As glacier retreats these terraces of deposited material are left on valley side.

Question 10

What are two ice contact fluvio glacial features

Answer 10

Eskers and kame terraces