The purpose of this unit of work is to introduce students to a fascinating area of physical geography: glacial environments
What is the difference between weathering and erosion?
How does ice erosion work?
What are the main landforms of glacial erosion?
Where did the roche moutonnée get its name?
Weathering is the breaking-apart of rocks in a particular place. You can see the effects of weathering all around you, where roads and pavements become cracked and damaged due to their exposure to the weather and other types of damage. Erosion is a much wider term. It describes both the breaking apart of rocks and also their removal, for instance by a moving ice sheet. When you look at a valley in the landscape, you see the effects of erosion. A gap has been created, perhaps by the action of running water and the local weather. However, the broken-down rocks have also been removed, leaving the valley shape.
Key weathering processes include:
Rainwater freezes at night in small hair-line cracks and widens them. Water expands by 10% when it freezes to form ice. Over time, cracks get wider and wider
Daytime, night-time and seasonal temperature changes cause minerals in the tarmac to expand and contract as they are heated and cooled - which can be very damaging
Rainwater contains mild acids that can dissolve some minerals over long periods of time
Tree roots are growing underneath the tarmac and they break it apart. This is biological weathering
Humans walk on the path every day and their trampling damages it
Key ice erosion processes include: As the ice moves over a rock surface, it freezes around loose or weak sections, pulling them away. This is called plucking (more precisely, it involves pressure melting of ice at the base of a glacier and subsequent re-freezing around disintegrating bedrock. It is a more advanced scientific concept and need not be explained at this higher level unless students require further stretch and challenge). Once pieces of jagged rock are being carried by the ice, they have a ‘sandpaper effect' on other land surfaces, helping to cause further destruction. This is called abrasion.
Ice creates unique landforms in upland areas. Glacial places in the world are home to unique landforms that give them a special character that is not found elsewhere. Exposure of these special landforms is on-going, with some revealed at the end of the last ice age and others only becoming uncovered in recent years as ice has started to melt again. Examples can be seen throughout the UK that were exposed 10,000 years ago when ice melted. Some of the key landforms include:
U-shaped valley (a deep, wide valley created by ice erosion that replaces the V-shaped valley associated with fluvial erosion in a more temperate environment)
Corrie (an amphitheatre-shaped hollow found on mountain sides especially those with a north-facing aspect; snow accumulates well where there is less melting by sunlight and rotational movement of the ice mass has over-deepened this section of mountain-side)
Arête (a sharp ridge that results from two corries forming on adjacent slopes)
Pyramidal peak (a distinctive-shaped mountain whose sides are marked with a number of corries)
Treatment of additional erosional landforms may be possible if time allows (for example hanging valley, truncated spurs).
The erosion processes of abrasion and plucking are very important in the creation of these landforms. In addition, ice moves in different ways from water - which can sometimes result in the scouring effect that allows deep rock basins to be created on the sides of mountains (corries). Freeze-thaw weathering creates the rock-falls that cover active glaciers with the mantle of debris that can be seen in photographs.
The roche moutonnée is a resistant and tough outcrop of rock found on the floor of a U-shaped valley that a glacier once occupied. You can see scratches called striations on it, caused by moving ice.
In French, roche moutonnée means ‘sheep-backed rock' or ‘fleecy rock'. This glacially-eroded landform is thought to resemble a grazing sheep.
Read the introductory (blue) section of the erosion and weathering document which gives the definitions of weathering and erosion.
Now that you understand the difference between the two processes, see if you can spot some examples of landforms created by each process on this website.
Alternatively, your teacher might give you some images to look at.
Now look at the rest of the Erosion and Weathering document you used in the starter activity. This gives some extra details about weathering and erosion. It also explains how ice erosion works.
Complete the activities on the final page of the document which will get you thinking about how these processes work in different environments around the world.
The glacial landforms PowerPoint presentation introduces you to some of the different types of landform that are created by glacial erosion.
See if you can memorise their names and what they look like. One way of doing this is by teaching yourself Kung-fu glaciation...
Here are some of the moves:
Funky snowflake: Jump up and down pretending to be fluttering downwards
Ice: Jump into position as if on a snowboard and shout "ice"
Basal slippage: Wiggle your hips in a circular motion
Corrie: Make a cutting action across your body with a cupped hand
Arête: Make a cutting action downwards
Pyramidal peak: Thrust your arm in the air
Then you have to put all the moves together to show how the landforms are created.
For example: Snow falls and compacts to form ice. The ice erodes the rock by basal slippage to create a corrie. Two corries together form an arête, and three corries together form a pyramidal peak.
Can you come up with your own movements for other processes, such as plucking, abrasion and freeze-thaw? Or other landforms such as U-shaped valleys?
Now that you have familiarised yourself with some glacial processes and landforms, have a go at the card sort exercise, matching key terms with their definitions.
A roche moutonnée is another example of a landform created by glacial erosion, but how did it get its rather strange name?
Think about the following five questions:
What does the landform itself look like?
What language has it been named in?
What might the name mean when translated into English?
Why was it given this name?
How was the landform created by glacial erosion?
To check your answers, take a look at the PowerPoint presentation which explains all.
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