Arete and pyramidal peak

Aretes and pyramidal peaks are important features of glacial erosion. Make sure you know how they are formed adn can draw a diagram to show this. If you don't read this note and check out scalloway revision for diagrams.

Aretes form when 2 corries meet and erode back to back on a mountain. When this happens a a very steep narrow piece of land is all that is left between the corries. This piece of land is called a ridge and when it is in between two corries it is called an arête. Look at the photo of the arête and make sure you can see the two corries back to back and the sharp piece of land in between.

It is not too difficult to imagine what would happen if another corrie formed on another part of the mountain. The mountain would be worn away on at least three sides, and only a large peak shaped like a pyramid would be left. This is called a pyramidal peak.

Corrie

Corrie Formation

Corries form when snow gathers in a small hole or hollow in the ground high up on a mountain. The snow does not melt but gets thicker and thicker each year and after hundreds of years it turns to ice. This is a glacier. The glacier will become too big for the hollow and will start to move down the hill. When this happens, it sticks to the back of the hollow and plucking takes place. This makes the back of the hollow very steep.

The rocks under the ice wear away the rocks on the bottom of the hollow. This is abrasion. This means that the hollow becomes deeper. When the ice melts, a very deep hollow with three steep sides is left.

Sometimes the hollow fills with water and makes a lake. This deep hollow is called a corrie, and the lake is called a tarn.

Formation of a corrie - simplified (you will need diagrams to accompany this note)

1. Snow gathers in a hollow and does not melt. This is the start of a glacier.
3. At the back of the hollow the ice sticks to the rocks and plucking occurs.
2. The glacier gets too big for the hollow and starts to move down the mountain.
4. At the bottom of the hollow the rocks in the ice rub against the rocks in the hollow. This is abrasion.
5. When the ice melts, a deep hollow called a corrie is left behind. It often fills with water and a tarn is made.

http://www.scalloway.org.uk/phyl13.htm - has good diagrams to show what a corrie looks like.

Type corrie into google images to see actual pictures.

Processes of Erosion

How ice erodes
Remember, ice erodes by:
Plucking - glacier ice freezes into cracks in rocks and when the glacier moves it pulls out chunks to leave a jagged surface
Abrasion - rocks stuck in the ice grind away the bedrock under the glacier
Freeze Thaw - water in cracks in the rock freezes and expands forcing open the gap. When the ice melts more water can get into the crack and freeze again. After many cycles of freezing and thawing lumps of rock are broken off the surface.

You must be able to dsecribe these processes in the credit exam eg do not simply say that corries are formed by plucking and abrasion - tell me what the processes actually do!

Glaciation Revision

Glaciation can be a difficult topic to remember . Check your revision checklists and use traffic lights to work out where you are struggling.
Remember you need to be able to draw diagrams for all the features we have covered so far.
*Corrie
*U-Shaped Valley
*Pyramidal Peak
* Arete
*Drumlin

You also need to know about the processes of erosion and be able to describe each process (Plucking, Abrasion, Freeze/Thaw)

You must be able to descrieb landuse and potential conflicts and should also be able to identify the featurse from a map.

There are some notes on this site and some links to other websites to help with revision of this topic.