Glaciers GCSE AQA

Ice cover in the UK during the LGM

North Uk - Covered by ice

South Uk - Permafrost with icy winds blowing off ice sheet and tundra vegetation similar to Siberia today

Freeze thaw weathering

Water seeps into cracks on rockface

Temperature falls at night and the water freezes

Water expands by 10% when it turns to ice, expanding the crack

The ice continues to melt and freeze again, widening the crack and large blocks of rock can be shattered apart by repeat cycles of this weathering

Plucking

Meltwater freezes around loose sections of rock and pulls them away from the rock face

Abrasion

Erosion caused by rocks and boulders embedded in the base of the glacier, acting like sandpaper against the ground, and larger rocks can cause scarring in the landscape known as striations

Basal sliding (5 steps)

1. Weight of the ice creates pressure at the base of the glacier

2. Creating warmth

3. Increases melting, meaning meltwater is present

4. Meltwater provides lubrication so the glacier slides over the surface

   1. Gravity causes the movement to be downhill

Rotational slip (5 steps)

1. Snowflakes settle in a hollow

2. As more snow falls, the snow is compressed and air is squeezed out to form firn

3. With the pressure from more layers of snow, over 1000s of years the firn becomes glacier ice.

4. Even though the ice is trapped in a hollow, gravity encourages it to move

   1. This movement is circular and known as rotational slip, which causes ice to pull away from the back wall creating a crevasse

Outwash

• Deposited by water

• Sorted —> largest sediment first

• Rounded by attrition

Till

• Deposited by ice

• Unsorted

• Angular

Attrition

A form of erosion where rocks collide and become smaller and smoother

Glacial till formation

1. Material is constantly brought down by the ice from upland areas to the lowland areas, with the glacier acting like a conveyor belt

2. The section of ice that the material is carried on reaches the warmer lowland areas

3. This ice temporarily becomes the snout, then melts, and the material it was carrying is deposited

Glacial outwash formation

1. During the summer months, and in warmer lowland areas specifically, meltwater pours off the snout

2. Meltwater rivers transport vast amounts of water from glaciers and ice sheets into the oceans

3. These rivers carry large amounts of sediment called glacial outwash, which is rounded and reduced in size by attrition

4. Larger material is deposited first as it is heavier and fine material is deposited furthest from the glacier

Reason for difference in size range between glacial till and glacial outwash

Till has a wider range of materials since it consists of materials transported by ice so everything is picked up, rather than larger rocks being left behind by water

How does a glacier carry material on the surface?

Freeze thaw weathering on the mountainsides causes the deposition of blocks of rock that become detached from the rock face and so fall onto the ice below

How does a glacier carry material inside the glacier itself?

• Some rocks fall into crevasses, resulting in a build up of material inside the glacier

• The rocks atop the glacier can be buried beneath fresh snow, particularly in upland areas

How does a glacier carry material beneath the glacier?

Plucking tears away rock at the bed of the glacier that then becomes embedded in the base of the moving ice

Corrie formation (5 steps)

1. Starts as the hollow in which a glacier begins

2. As the glacier moves, plucking and freeze thaw weathering occurs at the back wall of the corrie, making it steeper

3. Movement also causes plucking and abrasion to erode the hollow and make it deeper

4. As the glacier flows out of the hollow and into the main valley glacier it erodes less at the front edge, forming a rock lip

5. Sometimes when the ice melts a corrie lake or tarn remains at the bottom of the corrie

Arete

A sharp ridge where 2 corries cut back into a mountain

Pyramidal peak

A mountain top carved and steepened by weathering and erosion forms corries around it

Formation of an arete

2 corries erode back to back, leaving behind a sharp ridge of rock between them when the ice melts at the end of glaciation

Ribbon lake

Long, narrow lakes on the floor of a glacial valley which occur where glacier have eroded softer rock, creating rock basins.

Eg. Loch ness, Loch Lomond, Lake Windemere

Misfit streams

Small streams in large glaciated valleys, which are not in proportion with the size of the U-shaped valley.

Formation of a glacial trough/U-shaped valley

• It is a V shaped valley prior to glaciation, where a river meanders forming interlocking spurs.

• During glaciation a glacier fills the valley and plucking and abrasion widens and deepens the valley and makes it straighter.

• After glaciation, the U-shaped valley remains with steep valley sides, a flat floor and potentially a misfit stream or ribbon lake

Formation of a hanging valley

• Prior to glaciation it is a tributary valley beside a main V-shaped valley, with a tributary that runs out of it to meet the main river meandering around interlocking spurs in the main valley

• During glaciation a large glacier forms in the main valley and a smaller one in the tributary valley, which erodes slower

• The main glacier widens, steepens, straightens and deepens the main valley, but due to differential erosion, the tributary valley is left hanging above the main one, forming a hanging valley with a waterfall running down to meet what is potentially a misfit stream or ribbon lake.

Interlocking spurs

Projecting ridges that extend alternately from opposite sides of a valley down which a winding river flows between them.

Truncated spurs

When the glacier erodes the old river valley with interlocking spurs, the spurs are cut off, creating truncated spurs, which are steep slopes that run down from the valley sides on either side.

Erratics

Pieces of rock that differ from the bedrock in which they are found. They are often transported by glaciers over thousands of miles, and scientists can use them to trace the history of glaciation by seeing where the rocks came from.

Lateral moraine

Ridge of material that runs along the edges of a glacial trough, and as the ice melts and the glacier becomes smaller it is deposited on the valley floor. It is formed by freeze-thaw weathering high on the valley sides.

Medial Moraine

When 2 glaciers meet, 2 lateral moraines merge forming a large ridge of rock debris

Ground moraine

Material gets lodged and deposited beneath the glacier and it covers large parts of the UK as a legacy of the last ice age since vast amounts can be produced when glaciers disappear entirely.

Terminal Moraine

Enormous ridge of material that gets bulldozed by the snout, allowing us to work out how far the ice advanced during the last ice age.

Drumlins

Smooth hills that are typically 30-40m high and 300-400m long, all lying in the same direction and have similar shapes with a blunt end and a tapered end.

Formation of a drumlin

1. Ice is pushed forward across a lowland area but it is overloaded and melting

2. Any small obstacle causes deposition

3. More deposition occurs around the upstream end of the obstacle forming the blunt end

4. The rest of the boulder clay is then moulded into shape by the obstacle to form the tapered end downstream

Location of Lake District

• Northwest of England

• Near the coast

• Became a national park in 1951

• Famous for mountains, hills + lakes