OCR A Level GL - 7. OCR A Level GL 2.2b DEPOSITIONAL LANDFORMS

Question 1

What is a moraine?

Answer 1

distinct ridges or mounds of debris that are laid down directly by a glacier or pushed up by it.

Question 2

How big are moraines?

Answer 2

They range from low-relief ridges of ~1 m high and ~1 m wide formed at the snout of actively retreating valley glaciers, to vast ‘till plains’ left behind by former continental ice sheets.​

Question 3

What are moraines made of?

Answer 3

they consist of loose sediment and rock debris deposited by glacier ice, known as till. All of this material has come from rock material that has fallen onto or been eroded by the glacier

Question 4

Why are moraines important?

Answer 4

they help to understand past environments. Terminal moraines, for example, mark the maximum extent of a glacier advance and are used by glaciologists to reconstruct the former size of glaciers and ice sheets that have now shrunk or disappeared entirely.​

Question 5

What is a terminal moraine?

Answer 5

A ridge that marks the maximum limit of a glacier advance.

Question 6

What sizes can terminal moraines be?

Answer 6

The largest terminal moraines are formed by major continental ice sheets and can be over 100 m in height and 10s of kilometres long.

Question 7

What is a lateral moraine?

Answer 7

A long mound of material deposited along the sides of a glacier

Question 8

What size can lateral moraines be?

Answer 8

they can reach heights of more than 100 metres.

Question 9

What is a recessional moraine?

Answer 9

moraines that are found behind a terminal moraine. They form during short-lived phases of glacier advance

Question 10

What are medial moraines?

Answer 10

these form where lateral moraines meet at the confluence of two valley glaciers.

Question 11

What is an erratic?

Answer 11

rocks that have been transported by ice and deposited elsewhere. ​ The type of rock (lithology) that the glacial erratic is made from is different to the lithology of the bedrock where the erratic is deposited.​

Question 12

Why are erratics useful?

Answer 12

because erratics have a distinctive rock type, their source outcrop can be identified and located. They are therefore useful in:
1. reconstructing past glacier flow directions,
2. identifying the timing of glacier retreat, and
3. identifying the type of glacier flow.

Question 13

What is a drumlin?

Answer 13

Smooth, elongated mounds of till that are smoothed in the direction of the glacier’s flow

Question 14

What are the general sizes of drumlins?

Answer 14

can be 50 meters high and over one kilometre in length

Question 15

What are groups of drumlins known as?

Answer 15

a swarm

Question 16

What are till sheets?

Answer 16

wide areas of flat relief where there is a covering of unstratified glacial till (sand and gravel) often found behind terminal moraine.

Question 17

Give an example of a till sheet and its characteristics in the UK

Answer 17

In East Anglia, the till sheet is on average 30-50m deep and was formed by several different ice advances between 480,000 and 425,000 years ago

Question 18

Give an example of a till sheet and its characteristics in the USA

Answer 18

In Minnesota, the Des Moines till deposits are made of limestone, shale and granite at an average of 100m deep and some are over 160m. They were formed between 75,000 and 14,000 years ago