Glacial Landforms - Cool Geography

Home » A Hanging Valley Is Formed When A » Glacial Landforms - Cool Geography

Maybe your like

Back to Main Page Back to GCSE Page Back to Rivers, Coasts and Glaciers

Glacial Landforms: Corries/cirques/cwm Aretes and pyramidal peaks U shaped valleys and truncated spurs Ribbon lakes Hanging valleys Moraine Tasks

Image of Alaskan Glacial scenery

How Corries Form

Corries form in hollows where snow can accumulate. In the Northern hemisphere this tends to be on North facing slops which because of their aspect are slightly protected from the sun, which allows snow to lie on the ground for longer and accumulate. The snow compacts into ice and this accumulates over many years to com pact and grow into a corrie/cirque glacier. This moves down hill because of gravity, the mass of the ice, water at it's base and the slope it is on. The ice freezes to the back wall and as it does plucks rock out steepening the back wall. Freeze Thaw and frost shatter above the hollow on exposed rocks shatters the rock and deliver shattered rock known as scree to the ice (both on top of the ice, within it and under it).

This material from plucking and frost shatter is then moved along under the ice abrading the hollow by scratching the surface rock.This creates a steep back wall and a hollow known as a corrie or cirque. At the front edge of the corrie the ice thins out at is speeds up on its journey down valley, and this area is eroded less and crevasses form. This leaves a lip of rock. When the ice melts a corrie lake can form. View an animation of this process.

In France and Switzerland Corries (the Scottish word) are known as Cirques (because of their near CIRcular shape), Coombe in England and in Wales it is Cwm. Back to the top

Arêtes and pyramidal peaks

Where 2 corries occur back to back, they can erode backwards through the processes outlined above. As these corries erode backwards they steepen the back walls in both corries, which eventually leaves a steep knife edged ridge called an Arête. Where 3 or more corries erode backwards towards one another, this can create a Pyramidal peak, a steep sided pointed mountain like the Matterhorn.

U – Shaped Valleys.

As corrie glaciers leave their source regions and descend down old river valleys they can make huge changes to the landscape. One of the major change they make is to the V-shaped valleys characteristic of the upper reaches of river valleys. The glaciers basically alter this V shape into a U, by creating a steep sided, wide valley in the shape of the letter U.They are formed by a valley glacier that moves down the valley because of gravity.

As the glacier moves down the valley it plucks the rock from beneath and those rocks then rub against the bed of the valley, eroding it further.This deepens and widens the valley. At the front end of the glacier it acts like a bulldozer, shifting and removing soil, plucking rock from interlocking spurs and truncating them. This creates Truncated Spurs, which are interlocking spurs without the land that interlocks! Originally, truncated spurs are created as a river erodes the upper valley it cuts down into the rock and meanders in and out of the surrounding rock. During glaciations this rock is removed by descending ice sheets.

 U-shaped valley Back to the top

Ribbon Lakes.

Within U shaped valleys you can often find Ribbon lakes (at the bottom of the picture above). These are long and thin lakes that collect from melt water and rain water after the glacier has melted.During glaciations the glacier erodes some parts of the valley floor more than others. This could be because of varying strengths of the bedrock or because there is thicker ice in one region of the glacier than another or because there is more moraine abrading the ground in one region than another. When the glacier melts water fills the depressions (holes) where the valley floor was eroded most. These lakes can also form because melt water from receding glaciers is trapped behind Moraine, which is discussed below.

Hanging Valleys

Within glacial valleys there are main glaciers and smaller tributary glaciers (just like with rivers). The main glacier can erode its valley to a much greater extent because they are wider, deeper, have more mass and more moraine to use as erosive tools. The tributary valley glaciers are smaller, have less mass and moraine hence erode their valley less. This means that the main valley is deeper, wider and steeper, and this becomes really evident post glaciation, when the tributary glacier is left hanging high above the main valley. When rivers return, they often form waterfalls in these hanging valleys. This can all be seen in the images below. You can also see a fantastic animation of how hanging valleys are created here.

Stage 1 in Hanging valley formation How hanging valleys form Stage 2 in hanging valley formation Hanging valley creation
Milford Sound Hanging valley Mlford sound hanging valley from distance

Back to the top

Moraine

This is the material produced by glacial erosion. The material tends to be unsorted (it contains really huge boulders and at the same time a fine powder called glacial flour). It also tends to be very angular, as the processes that form the material involve freezing and shattering. There are different types of moraine including: Ground moraine - which is moraine spread all over the ground as a glacier retreats up valley in warmer times Terminal moraine - which are rocks deposited in a ridge at the maximum advance of the ice Lateral Moraine which are ridges of moraine that come from the valley sides and run parallel to those valley sides Medial Moraine - these are a ridge of rocks running down the middle of a valley formed by 2 lateral moraines from 2 glaciers coming together. You can see an animation of moraine here (click on "watch glacier movie") .

 Moraine types Back to the top

Tasks 1) Have a go at a Hot Potatoes Match up exercise

2) Put together an page of images to show the range of glacial landforms using the UWSP web site

3) Have a go at this Ordnance survey map exercise

4) Glaciers penalty shoot out from juicy geography

5) Label the Franz Joseph Glacier

6) Try these cloze exercises - Corries hard version, Corries easier version, U shaped Valleys hard and U shaped Valleys easier

Tag » A Hanging Valley Is Formed When A