© Boardworks Ltd 2005 1 of 40 Glaciated Landscapes ~ Landforms © Boardworks Ltd 2005

© Boardworks Ltd 20051 of 401 of 40

Glaciated Landscapes

~ Landforms

© Boardworks Ltd 2005

© Boardworks Ltd 20052 of 40

By the end of this cycle I will be able to:• Recognise features of glacial erosion on a sketch• Describe/explain the formation of features of glacial

erosion eg corrie, arete, pyramidal peak, u-shaped valley, and hanging valley

• Recognise features of glacial deposition on a sketch• Identify glacial features on OS maps

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Landforms created by glacial erosion

CorriesThe landforms created by glacial erosion are:

Arêtes

Pyramidal peaks

Glacial troughs (U-shaped valley)

Truncated spursHanging valleys


How is a corrie formed?

Snow collects in a natural hollow on the side of a mountain. Over time, further snow collects in the hollow. This extra weight compresses the snow underneath, turning it into ice.

The hollow is deepened and widened by the corrie glacier through the processes of abrasion and plucking.

rock lip

This overdeepening leads to an ‘armchair’ shape characteristic of a corrie and causes a ‘rock lip’ to be formed.


Corrie formation


Diagram of a corrie


Explain the formation of a corrie


tarn

bowl-shaped corrie

steep backwall

Example of a corrie: Cwm Idwal


Drawing a fieldsketch of Cwm Idwal


Fieldsketch of Cwm Idwal looking south-west

tarn

steep backwall

fence

shattered rock




Arêtes

Pyramidal peaks




Formation of an arête

Arêtes are ‘knife-edged’ ridges formed between two corries.


Pyramidal peaks are formed when three or more corries cut backwards into the same mountain.

Formation of a pyramidal peak

corrietarn

arête


Label the pyramidal peak diagram




Arêtes

Pyramidal peaks




Formation of a glacial trough


How and why do these valleys differ?

Unlike a river, a glacier fills the entire valley and so has much more power to erode.

It does not have to wind around interlocking spurs and can widen, deepen and straighten its valley.

river valley glaciated valley


Characteristics of a glacial trough

truncated spurs

hanging valley misfit stream

wide and flat valley floor

steep valley sides

What are the characteristics of a glacial trough?

Interlocking spurs are truncated as the glacier cuts straight through the landscape.

Between truncated spurs are hanging valleys which have not been eroded as deeply as the main valley.

The river that flows through the valley after the ice age is described as a misfit stream.


Hanging valley at Ogwen Falls, Snowdonia

Ogwen Falls, Snowdonia


Nant Ffrancon Valley, Snowdonia

Produce an annotated sketch to show that this is a glaciated valley.

What evidence is there to suggest that this valley has been shaped by ice?


What landforms are created by glacial erosion?What landforms are created by glacial deposition?How can glacial features be identified on maps?

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Landforms created by glacial deposition

Moraines

Drumlins

Erratics

Porsmork Valley, Iceland.

What landforms are created by glacial deposition?


What is moraine?

Moraine is a type of landform that is created when a glacier deposits the material (till) that it has been transporting. It is made up of unsorted angular rocks. There are several types of moraine:

Lateral

Medial

Ground

Recessional

Terminal

Unsorted, angular rocks make up this moraine found in the Porsmork Valley, SW Iceland.


How is moraine deposited?



Moraines

Drumlins

Erratics




How are drumlins formed?

Drumlins are formed of till. They are elongated features that can reach a kilometre or more in length, 500m or so in width and over 50m in height.

There is still some debate about how drumlins are formed, but the most widely accepted idea is that they were formed when the ice became overloaded with sediment.

It is common to find several drumlins grouped together. A collection of drumlins is called a swarm.


Features of glacial deposition


Do you know your moraines?



Moraines

Drumlins

Erratics




What are erratics?

An erratic is a boulder that is different to the bedrock upon which it is sitting. They have been transported and deposited by a glacier. Therefore erratics are useful indicators of patterns of former ice flow.


Examination question

Study the photograph.

Is this the zone of accumulation or ablation? Give a reason for your answer.

Describe the characteristics of the material that has been transported by this glacier.



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Formation of ribbon lakes

When a glacier moves along its valley, areas of softer rock may be eroded more easily, or the glacier may be joined by a tributary glacier to increase its power to erode. When the glacier retreats, the deepened sections fill with meltwater and become lakes. Deposition of moraine across the valley can also act as a dam, trapping the meltwater and thereby creating a ribbon lake.

Ribbon lakes are long, narrow lakes found on the valley floors of glacial troughs. They can be formed due to a combination of erosion and depositional processes.

Llyn Ogwen (a ribbon lake in Snowdonia)


How are ribbon lakes formed?


Learning objectives



Identifying glacial troughs

glacial troughs Map of Snowdonia


Identifying glacial features on maps


List three pieces of map evidence to show that this area was glaciated.

Examination question


Glaciation quiz


Key ideas

Corries, arêtes, pyramidal peaks and glacial troughs are created by glacial erosion.

Moraines, drumlins and erratics are the result of glacial deposition.

Moraine is a type of landform that is created when a glacier deposits the material (till) that it has been transporting.

There are five main types of moraine.

Contour patterns on maps can give a clear indication as to whether a landscape has been glaciated.

Documents

© Boardworks Ltd 2005 1 of 40 Glaciated Landscapes ~ Landforms © Boardworks Ltd 2005