Glaciers: Shaping the Land

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Glaciers: Shaping the Land

Open with the idea that ice may seem still, but glaciers are powerful moving systems that reshape whole landscapes over long periods.

Learning goal

I can explain how glaciers move and how glacial processes create key landforms.

What words come to mind when you hear glacial landscape?

Use this to surface prior knowledge such as ice, valley, erosion, mountains, moraine or cold. Briefly address misconceptions before teaching begins.

What is a glacier?

• A glacier is a large mass of ice that lasts all year

• It forms where snowfall builds up over many years

• Over time, the snow is compressed into dense glacial ice

• Glaciers are found where more snow falls than melts

Make clear that a glacier is not just any patch of ice or snow. It must persist and build up over time.

Accumulation and ablation

A glacier grows or shrinks depending on its mass balance. Accumulation is the gain of snow and ice. Ablation is the loss of ice by melting, evaporation and calving. When accumulation is greater than ablation, the glacier advances; when ablation is greater, it retreats.

Students often think a retreating glacier moves backwards uphill. Clarify that the ice still flows downslope; the snout retreats because more ice is lost than replaced.

From snow to ice

• Fresh snow builds up in the upper part of the glacier

• Snow is buried, compressed and turns into firn

• Further الضغط creates solid glacial ice

• This process can take many years

If needed, explain firn as old, compacted snow that is between fresh snow and glacier ice.

Why glaciers move

Gravity pulls the heavy mass of ice downslope. Although glaciers seem fixed, the ice deforms and flows slowly under its own weight. This movement is strongest where the ice is thickest and the slope is steeper.

Link movement to place and slope, keeping the geography lens on systems and landscape change.

How ice flows

• Internal flow: ice crystals deform and the ice bends

• Basal slip: the glacier slides over the ground below

• Meltwater at the base can reduce friction

• Different speeds create cracks called crevasses

You do not need to go deeply into glacier physics; focus on the two movement mechanisms and their effect on the landscape.

When does a glacier advance?

A

When ablation is greater

B

When accumulation is greater

C

When the valley is flatter

D

When crevasses close

Checks mass balance. A common misconception is that glacier advance depends mainly on slope rather than on accumulation exceeding ablation.

Complete the glacier movement summary

A glacier forms where more snow falls than melts over many years. Snow is compressed into firn and then glacial ice. Gravity pulls the ice downslope, and movement can happen by internal flow or basal slip.

melts

firn

downslope

basal slip

retreats

till

upland

abrasion

corrie

All four blanks are key terms from slides 2 to 6. Remind students that a retreating glacier can still move downslope.

Three glacial processes

Glaciers shape landscapes through erosion, transportation and deposition. Erosion wears away rock, transportation moves debris within or on the ice, and deposition drops material when the glacier loses energy or melts.

This slide acts as the bridge from glacier movement to landform creation.

Plucking and abrasion

• Plucking happens when meltwater freezes in cracks in rock

• As the glacier moves, it pulls loose blocks away

• Abrasion happens when rock fragments in the ice scrape the valley floor and sides

• Abrasion smooths rock and leaves scratches called striations

Stress the contrast: plucking removes blocks; abrasion grinds and smooths.

Transportation by ice

• Debris can be carried on the surface, inside the ice or at the base

• Material moved by a glacier is called till when it is unsorted

• Large and small fragments can travel together

• Transported material helps abrasion as the glacier moves

Distinguish glacier transport from rivers: glacier deposits are usually unsorted, unlike many river deposits.

Deposition by glaciers

Deposition takes place when ice melts and can no longer carry its load. Because glaciers drop material of many sizes together, their deposits are often angular, mixed and unsorted. These deposits build distinctive landforms that can still be identified after the ice has gone.

Which process pulls blocks of rock away?

A

Deposition

B

Abrasion

C

Plucking

D

Transportation

Tests the contrast between plucking and abrasion after the process block.

How is abrasion different from plucking?

Expected elements: abrasion scrapes and smooths rock using debris in the ice, often leaving striations; plucking removes loosened blocks where water freezes in cracks. Students should show the contrast in what each process does.

How a corrie forms

Snow collects in a hollow high on a mountainside. Plucking steepens the back wall and abrasion deepens the basin. Over time, this creates an armchair-shaped hollow called a corrie, often with a steep front edge known as a lip.

You may note that a small lake can later fill the basin, but keep the focus on landform formation.

Arêtes and pyramidal peaks

• An arête is a narrow, sharp ridge between two corries or glacial valleys

• A pyramidal peak forms where three or more corries cut back into a mountain

• Both are created by intense freeze-thaw weathering and glacial erosion

The Matterhorn is a classic example of a pyramidal peak if you want a named case here as well.

U-shaped valleys

• River valleys are usually narrow and V-shaped

• A glacier widens, deepens and straightens the valley

• This creates steep sides and a broad, flat floor

• Truncated spurs and hanging valleys are common nearby

Contrast with river action to help students identify glacial landscapes from photographs or maps.

What creates a pyramidal peak?

A

One glacier widening a valley

B

Three or more corries eroding back

C

A terminal moraine building up

D

Till smoothing the summit

Checks understanding of erosional landforms and avoids confusion with depositional features.

Complete the erosional landforms summary

A corrie is an armchair-shaped hollow formed high on a mountainside. An arête is a sharp ridge between two corries. A glacier can also turn a V-shaped river valley into a U-shaped valley with steep sides and a broad floor.

corrie

arête

U-shaped valley

moraine

drumlin

erratic

basal slip

Each blank matches a distinct landform definition from slides 11 to 13.

Moraines

• Moraines are ridges of till left by a glacier

• Lateral moraine forms along the sides

• Medial moraine forms where two glaciers join

• Terminal moraine marks the glacier's furthest advance

If helpful, mention that recessional moraines can also form during pauses in retreat, but keep the main types as the priority.

Drumlins and erratics

• Drumlins are elongated hills of till shaped by moving ice

• Their long axis shows the direction of ice movement

• Erratics are large boulders left in a different rock area from where they came

• They are evidence that the glacier transported rock over distance

Students often confuse drumlins with moraines. Emphasise that drumlins are streamlined hills, not ridges marking an ice edge.

Named example: Glencoe, Scotland

• Glencoe is a famous glaciated landscape in the Scottish Highlands

• Glaciers deepened and widened the valley into a U-shape

• Steep valley sides and truncated spurs show strong erosion

• Deposits in the area also show where ice once moved and melted

Use Glencoe as a clear UK example students may meet in GCSE geography. Keep the focus on identifying processes from visible landforms.

Reading a glacial landscape

A glacial landscape can be identified by linking landforms to processes. Corries, arêtes, pyramidal peaks and U-shaped valleys show strong erosion by moving ice. Moraines, drumlins and erratics show where material was transported and deposited.

This is the resolving slide for the central question: glaciers move, erode, transport and deposit, and those processes leave a recognisable landscape pattern.

Which feature marks the glacier's furthest advance?

A

Medial moraine

B

Erratic

C

Drumlin

D

Terminal moraine

Targets a common confusion between moraine types and drumlins.

Which clue is strongest evidence of glacial deposition?

1

Moraine ridge

2

U-shaped valley

3

Arête ridge

4

Corrie basin

How does Glencoe show glacier action?

Expected elements: Glencoe shows glacial erosion through its U-shaped valley, steep sides and truncated spurs; students may also mention deposits showing transport and melting. Accept any clear process-to-landform link.

What is one thing you will remember from this lesson?

Which part of the lesson helped you understand best?

Glossary

glacier - a large mass of ice formed from compacted snow that moves slowly over land

accumulation - the gain of snow and ice in a glacier system

ablation - the loss of ice from a glacier through melting, evaporation or calving

firn - compacted old snow that is changing into glacial ice

mass balance - the difference between accumulation and ablation

plucking - erosion where ice pulls blocks of rock from the ground

abrasion - erosion where rock fragments in the ice scrape the land

Glossary

till - unsorted material deposited directly by a glacier

corrie - an armchair-shaped hollow formed by glacial erosion on a mountainside

arête - a narrow ridge formed between two corries or glacial valleys

pyramidal peak - a pointed mountain summit formed where several corries erode back

U-shaped valley - a wide, steep-sided valley carved by a glacier

moraine - a ridge or accumulation of till left by a glacier

drumlin - an elongated hill of till shaped by moving glacier ice

Glossary

erratic - a boulder carried by a glacier and left in a different rock area from its origin

striations - scratches cut into rock by debris carried in moving ice

basal slip - glacier movement caused by sliding at the base

internal flow - glacier movement caused by ice deforming under pressure

truncated spur - a valley-side ridge cut off by glacier erosion

hanging valley - a smaller tributary valley left above the main glacial valley floor