GCSE · Geography · AQA · Spec 8035

Erratics, drumlins and types of moraine

The ice melted long ago. So how can you tell a glacier was ever here? Read what it left: jumbled ridges, long hills of moraine, and boulders of the wrong rock.

Glacial deposition · Moraine

Where does each moraine form?
Valley sideValley sideTwo glaciers joinSnout

View: Glacier flowing. Showing 3 layers: Valley, Till on the valley floor, Flowing glacier

View

Explore

now tap each moraine ↓

While the glacier flows, it carries rock and soil with it: underneath the ice, along its sides and, below the point where two glaciers join, down its middle.

Switch between the flowing glacier and the melted valley, then tap each type of moraine to see where it forms and why.

Drumlins · Put it in order

How does a pile of sediment become a drumlin?

Put the four stages of drumlin formation in order, first to last.

1 · First stage4 · Last stage

  1. Ice flow and pressure compact the sediment and mould it into an elongated hill

  2. The glacier moves downhill, carrying unsorted sediment at its base

  3. The glacier melts and retreats, leaving the hill behind

  4. An obstacle, such as a rock or a mound of debris, makes ice and sediment build up around it

Predict, then check

Side-on, a drumlin isn't symmetrical. One end is steep, and the other end slopes away gently.

The ice that shaped this drumlin was flowing towards one of its two ends. Which one?

Erratics · What do you think?

How would you know a boulder is an erratic?

You're walking through a valley that was once filled by a glacier, and you come across a large boulder sitting on its own.

Which is closest to what you think right now?
How sure are you?

Put it all together

Which landform is it?

Pick a clue, then choose the landform it describes.

Still to sort

Ground moraine (0)

Dropped beneath the glacier

Lateral moraine (0)

Along the glacier's sides

Where the line is: Lateral runs along the SIDES of the glacier. Medial runs down the MIDDLE, below the point where two glaciers joined.

Medial moraine (0)

Down the centre, below a junction

Terminal moraine (0)

At the snout, the furthest point

Drumlin (0)

A long hill of moulded moraine

Where the line is: A drumlin is a hill of moraine with a steep end and a gentle end, not a ridge along the edge of the ice.

Erratic (0)

A boulder of out-of-place rock

Where the line is: An erratic is judged by its rock, not its size: it has to be different from the rocks around it.

7 of 7 still to sort.

Now write it

Explain a drumlin in your own words

Explain how a drumlin forms and what its shape shows about the glacier that formed it. [4 marks]

0 words · your answer stays on this page and is not sent anywhere.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

The glacier has gone, but it left its fingerprints all over the valley. Here's how to read them.

What you need to know

  • Glaciers transport the material they erode and then deposit it, creating landforms such as erratics, drumlins and moraine.
  • Glacial deposition happens when a glacier melts: it can no longer carry its load, so it drops the sediment, called glacial till.
  • Moraine is unsorted debris (rocks, clay and soil) deposited by a glacier. Its type depends on where it was carried: ground, lateral, medial or terminal.
  • A drumlin is an elongated hill of moraine moulded by moving ice. Its shape shows which way the ice flowed.
  • An erratic is a large boulder whose rock doesn't match the local rock, because a glacier may have carried it hundreds of kilometres.

The big picture

When a glacier melts, it can no longer carry the material it has eroded, so it drops it as unsorted till. Moraine is named by where that debris was carried: ground moraine beneath the glacier, lateral along its sides, medial down the middle where two glaciers joined, and terminal at the snout, marking the furthest point the ice reached. Drumlins are long hills of moraine moulded by moving ice, with a steep stoss end facing up the valley and a gentle lee slope facing the way the ice flowed. Erratics are boulders whose rock doesn't match their surroundings, because the glacier may have carried them hundreds of kilometres.

Key points

1Ground moraine: carried at the base, deposited underneath the glacier as it melts.
2Lateral moraine: along the glacier's sides; it may be rock eroded from the valley walls.
3Medial moraine: down the centre, where two glaciers join and their lateral moraines combine.
4Terminal moraine: at the snout, marking the furthest point the glacier reached.
5Drumlin: steep stoss end faces up the valley; gentle lee slope faces the direction of ice flow. Drumlins often form swarms, a 'basket of eggs' landscape.
6Erratic: identified by rock that is different from the surrounding rocks, not by its size.

Worked example

Problem

A photograph shows a curved ridge of unsorted boulders, clay and soil stretching across a glaciated valley, at the place where the glacier's front edge once stood. Identify the landform and explain what it tells you about the glacier.

⚠ Watch out

Naming moraine by what it looks like instead of where it formed. Every moraine is a jumble of unsorted debris, so the type comes from its position: under the glacier, along its sides, down its middle or at its snout.

🧠

Memory hook

Moraines outline the glacier, drumlins point the way it flowed, and erratics are rocks that shouldn't be there. For the moraines, think of a bus terminal: the terminal moraine is the end of the line.

✓

Check yourself

Cover the page and sketch two glaciers joining into one. Can you mark where all four types of moraine form, and say in one sentence why each one ends up there?

Flashcards

(14)
What is glacial till?
The unsorted sediment a glacier deposits when it melts and can no longer carry it.
Why does a glacier deposit material?
When it melts, it can no longer carry its load, so it drops it.
What is moraine?
An accumulation of unsorted debris (rocks, clay and soil) deposited by a glacier, often forming ridges.
Ground moraine
Material carried at the base of the glacier and deposited underneath it as the ice melts.
Lateral moraine
Forms along the sides of a glacier. It may be rock eroded from the valley walls and carried on the ice's edge until the glacier retreated.
Medial moraine
Found in the centre of a glacier. It forms when two glaciers join and their lateral moraines combine.
Terminal moraine
Forms at the snout and marks the glacier's maximum extent, the furthest point it reached.
What is a drumlin?
An elongated hill made of deposited moraine (unsorted glacial sediment).
Stoss end vs lee slope
Stoss: the steeper end, facing up the valley. Lee: the gentler slope, facing the direction of ice flow.
What starts sediment building up into a drumlin?
An obstacle, such as a rock or a mound of debris, that makes ice and sediment collect around it.
Drumlin swarm
A cluster of drumlins. The landscape is often described as a 'basket of eggs'.
What is an erratic?
A large boulder deposited by a glacier whose geology doesn't match the area where it's found.
How do you identify an erratic?
Its rock is different from the surrounding rocks.
How can an erratic end up so far from its source rock?
A glacier may have transported it hundreds of kilometres before depositing it.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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