Lithosphere - glaciers

Glaciation

This is the process of which the land is covered by glaciers

Glaciers

Large, thick masses of ice that form on land when fallen snow is compressed over many years

Where does ice form?

In cold regions close to the poles or on areas of a high latitude, usually on north-facing slopes

What three processes are glaciers capable of doing?

• Deposition

• Erosion

• Transportation

Zone of accumulation

Areas where ice does not melt during summer leads to a build-up of pressure as more snow compacts into ice

Zone of ablation

As a glacier moves downhill due to gravity it will begin to melt, losing mass, creating meltwater streams that wash away sediment

Where is accumulation the greatest?

In the upper part of the glacier

Where is ablation the greatest?

In the lower part of the glacier

Advance

When temperatures are lower the glacier will move forwards due to the accumulation of ice

Retreat

When there is more ablation than accumulation and the glacier begins to melt

Accumulation of snow

How do glaciers accumulate?

If firn continues to build-up it will become more and more compacted, compressing the air out which forms glacial ice

What are the two process of glacial erosion?

Abrasion and plucking

Plucking

Glacial ice freezes onto rocks, moving it away as it pulls large rock pieces with it

Abrasion

Material carried by glaciers wears away the sides and floor of a valley

Weathering: freeze-thaw

Water repeatedly freezes and puts pressure on rocks that breaks them down

How is the eroded material from plucking further used?

The angular, jagged rock is picked up by the glacier as it moves downhill due to gravity, further eroding more rock

How is the eroded material from abrasion further used?

Large angular rocks widen and deepen a valley as striations are made on the surface

How is the weathered material from freeze-thaw further used?

The expansion of ice explodes open the sides of cliffs, steepening them, and as the scree falls the glacier picks them up

Plucking

Abrasion

Weathering: freeze-thaw

Corrie

A steep-sided armchair shaped hollow found on the side of a mountain

Formation of a corrie before glaciation

• Snow accumulates in hollows on north-facing mountains where more snow falls in winter and less melts in summer

• North and north-east facing slopes are more shaded, so snow lies longer which compresses into firn and then glacial ice

Formation of a corrie during glaciation

• The glacier begins to move downhill due to gravity

• The weight of the glacier pushes down causing rotational sliding, deepening the hollow

• Friction causes the ice to slow down at the front edge of the corrie, allowing a corrie lip to form

• A bergschrund crevasse opens at the back of the hollow, allowing meltwater and sediment to get to the base

Formation of a corrie after glaciation

• After the glacier has melted, a large armchair shaped hollow becomes visible

• The corrie lip helps to trap rainwater in the deepens hollow, forming a corrie loch

What are the three processes involved in the formation of a corrie during glaciation?

• Abrasion

• Plucking

• Weathering: freeze-thaw

Corrie

Named example: corrie

Corie Lagan, Skye

When explaining the formation of an arête or a pyramid peak what erosional formation much be explained before?

A corrie

Arête

Pyramidal peak

Formation of an arête

When two corries form back-to-back on a mountain, the back walls become steeper which creates a narrow ridge between the two corries

Formation of a pyramidal peak

When three or more corries form back-to-back on a mountain, the back walls become steeper which creates a serious of ridges and a jagged pyramidal peak in the centre

What are the six formations created through glacial erosion?

• Arête

• Corrie

• Hanging valley

• Pyramidal peak

• Ribbon lake

• U-shaped valley

What are the three formations created through glacial deposition?

• Drumlin

• Esker

• Terminal moraine

U-shaped valley

Glaciers abraded and plucked the sides and the valley floor of a v-shaped valley, smoothing it

What are the three processes involved in the formation of an u-shaped valley during glaciation?

• Abrasion

• Plucking

• Weathering: freeze-thaw

Characteristics of an u-shaped valley

• Misfit stream that winds along the valley floor

• Scree slopes formed from weathered rock fragments

• Steep valley sides with exposed rock

• Wide and flat valley floor

Characteristics of a corrie

• Contains a small lake known as a corrie loch

• North-facing hollow

• Raised lip at front

• Steep back wall

Formation of an u-shaped valley before glaciation

• Before glaciation, a river ran through a v-shaped valley

• Snow accumulated in north-facing hollows, where more snow falls in winter than melts in summer

• The snow is compressed to ice and the glacier moves downhill due to gravity

Formation of an u-shaped valley during glaciation

• The valley’s floor widens and deepens, turning it from a v-shape to an u-shape

• Loose rock fragments fall into the glacier as it moves downhill which will then move to the valley floor as scree

Formation of an u-shaped valley after glaciation

• When a period of glaciation is over, a deeper, wider, and straighter valley is left behind

• A misfit stream usually forms at the base of the valley floor as the glacier melts

U-shaped valley

Named example: u-shaped valley

Glen Torridon, Highlands

Truncated spur

Ridges of land (spurs) that stick out into the main valley and are then cut by the glacier as it moves through the valley

Hanging valley/truncated spur

When explaining the formation of a hanging valley or a ribbon lake what erosional formation much be explained before?

U-shaped valley

Hanging valley

A shallow valley carved out by a small tributary glacier which sits above the main valley

Formation of a hanging valley

• A glacier travels through a river tributary into the main valley

• The tributary glacier has less erosive power and so it becomes cut off by the glacier in the main valley

• A steep drop is found where the tributary valley meets the u-shaped valley

• If there is a misfit stream in the tributary valley, it will drop suddenly as a waterfall

• Once the ice has melted, it reveals the u-shaped valley with the tributary valley hanging about the main valley

Misfit stream/ribbon lake

Ribbon lake

A long, thin lake which forms on the floor of a u-shaped valley

Formation of a ribbon lake

• Harder, more resistant rock is less affected by the glacier

• Softer, less resistant rock is eroded more easily by the glacier, leaving a deeper area

• Moraine deposited by the glacier may also create a dam, trapping water

• When the glacier has retreated, water can collect in deep areas carved out by the glacier

Named example: ribbon lake

Lake Windermere, Lake District

Named example: hanging valley

Little Langdale, Lake District

Named example: pyramidal peak

Matterhorn, Switzerland

Named example: arête

Striding Edge, Lake District

What are the two ways a glacier deposits material?

Fluvio-glacial and till

Till

Unsorted and unstratified material deposited by the ice

Fluvio-glacial

Sorted and stratified material deposited by the meltwater flow

Terminal moraine

The material carried by the glacier as it is scraped from the valleys floor and sides through the three processes of erosion

What are the three types of terminal moraine?

• Lateral moraine

• Medial moraine

• Terminal moraine

Lateral moraine

Found at the sides of an u-shaped valley and are caused by the freeze-thaw of bare rocks above a glacier

Medial moraine

Found in the middle of an u-shaped valley running parallel with the valley sides caused when a tributary glacier joins the main valley

Terminal moraine

Ridges of unsorted material dumped directly by the ice

Formation of terminal moraine

• The glacier acts like a bulldozer, pushing sediment in front of its snout

• As it reaches lower altitudes/when temperatures rise, the glacier melts

• When the glacier melts, it loses power and deposits the material it was carrying

• Terminal moraine marks the furthest point the glacier reached

• The ridge across the valley is made up of till

• Once the ice has retreated, the terminal moraine can often form a natural dam creating a ribbon lake

Esker

Meandering ridges of fluvio-glacial deposits along a valley floor, formed by meltwater streams in or underneath a glacier

Formation of an esker

• In the zone of ablation, the glacier loses mass as it melts

• Meltwater streams travel through the glacier and deposit sediment in the channels underneath

• Deposits are sorted because heavier stones will be dropped first by the flowing water

• When the glacial period is over and the ice has melted, the raised ridges can be seen on the valley floor

Drumlin

Elongated rounded hills made up of till, often found in groups known as ‘baskets of eggs’

Formation of a drumlin

• Formed when the glacier becomes overloaded with sediments and deposits it

• As the glacier continues to flow past the sediment, it streamlines it

• The steep ‘stoss’ side faces up-valley and the more gently sloping ‘lee’ slope faces down-hill

• If there is a small obstacle on the ground, this may act as a trigger point and till can build up around it

Named example: drumlin

Glasgow

Three types of terminal moraine

Erosion

The wearing away and removal of materials such as rocks and soils

Glacial deposition

This is when glaciers melt and deposit materials

Glacial transportation

This is when glaciers move materials

What is the dominant processes of glacial transportation?

Gravity

What are the three processes involved in the formation of an arete during glaciation?

• Abrasion

• Plucking

• Weathering: freeze-thaw

What are the three processes involved in the formation of a pyramidal peak during glaciation?

• Abrasion

• Plucking

• Weathering: freeze-thaw

What are the three processes involved in the formation of a hanging valley during glaciation?

• Abrasion

• Plucking

• Weathering: freeze-thaw

What are the three processes involved in the formation of a ribbon lake during glaciation?

• Abrasion

• Plucking

• Weathering: freeze-thaw