Glacial landforms of deposition

Erratics

An is a large boulder carried by a glacier, sometimes many kilometres, and dropped when the ice melted.

It is usually a different rock from the rock it rests on, so it looks out of place.
By finding where its rock type comes from, geographers can work out the direction the ice moved.

For example: the Norber erratics, in the Yorkshire Dales, are dark boulders of older rock sitting on pale limestone.

Key terms

Drumlins

A is a smooth, oval hill of , shaped like an upside-down spoon or half an egg.

As the glacier moved, it carried a lot of till beneath it.
Where the ice was overloaded, or met an obstacle, it deposited the till.
The moving ice then moulded the till into a streamlined shape.

The steep, blunt end faces the way the ice came from.
The long, tapering end points the way the ice was moving.

Drumlins are often found in groups, called swarms, giving a landscape like a "basket of eggs".

Key terms

Moraines

A is a ridge or spread of material deposited by a glacier. There are four types:

Type	Where it forms
	Along the sides of the glacier, from rock that fell from the valley sides
	Down the middle, where two glaciers join and their lateral moraines merge
	A ridge across the valley at the glacier's furthest point, its , pushed and dropped there
Ground moraine	A sheet of till spread over the valley floor as the ice melted

Remember

Lateral at the sides; medial in the middle; terminal at the end; ground on the floor.

Key terms

Exam practice

Plan your own answer first, then open the model answers to see what each level looks like.

6 marks · about 6 minutes

Explain the formation of different types of moraine.

Explain means: Give the reasons why something happens, developing each point with "because" or "so".

Level 1 (Basic)· 2/6 marks (band 1–2)

Moraine is rock left behind by a glacier. There are different types like terminal moraine.

Why this level: Correct basic idea with one type named. To reach Level 2: explain how several types form and where each is found.

Level 2 (Clear)· 4/6 marks (band 3–4)

Lateral moraine forms along the sides of a glacier from rock broken off the valley sides. Terminal moraine forms at the glacier's snout, where material is dropped. When two glaciers join, their lateral moraines merge to form medial moraine.

Why this level: Clear explanation of three types. To reach Level 3: explain where the material comes from (freeze-thaw) and include ground moraine.

Level 3 (Detailed)· 6/6 marks (band 5–6)

Lateral moraine forms along a glacier's sides, from rock that freeze-thaw weathering broke off the valley sides and that fell onto the ice. Where two glaciers join, their lateral moraines merge into a medial moraine running down the middle of the new glacier. At the glacier's furthest point, its snout, material that the ice has pushed along and dropped builds up in a ridge across the valley: terminal moraine. As the ice melts and retreats, a sheet of till is spread unevenly over the valley floor as ground moraine. When the ice has gone, these ridges and sheets of unsorted material remain in the landscape.

Why this level: Detailed explanation of four types, where the material comes from and where each forms. This is Level 3.

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