• By the end of today's lessons you will be able to recognize Arêtes and explain the formation of glacial troughs and hanging valleys.

• Key Words;• Glaciated

trough• Truncated

spur• Hanging valley

What’s this?

Formation of an arête

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

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

Formation of a pyramidal peak

corrietarn

arête

Label the pyramidal peak diagram

1. Glaciers flowing out corries and moving downhill follow the easiest route, in most cases this is am existing river valley.

2. However glaciers often fill much of the valley and have a much greater erosive power.

3. Therefore instead of flowing around obstacles, such as interlocking spurs the glacier is able to widen, deepen and straighten the valley.

4. The result is a U shaped cross section known as a Glacial Trough.

Formation of a glacial trough

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.

1. As the glacier moves down the valley it works like a giant bulldozer.

2. It wears away anything in its path and smoothes the valley sides.

3. It removes the ends of interlocking spurs to leave steep, cliff like, Truncated Spurs.

4. Truncated Spurs are shortened or cut off ridges caused by glacial erosion.

1. Hanging valleys are formed as a result of erosion in the main and tributary valleys.

2. The floor of the tributary valleys is eroded at a slower rate than that of the main valley.

3. When the ice melts the tributary valley is left hanging above the main valley.

4. The stream in the hanging valley will now fall as a waterfall into the main valley.

Hanging Valley

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?

• Draw a before and after diagram of a glacial valley.

• Label the physical landforms and briefly explain their formation.