HOLGATE SCHOOL 
ENVIRONMENTAL EDUCATION 

'VIRTUAL VISITS'

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Landscapes created by glaciers.
Between 4 million and 10,000 years ago parts of Britain were covered by ice.  At the coldest period, the Arctic ice sheet stretched all the way from the North Pole to southern England.  At other times only the mountainous areas were affected by glaciers.  About 50,000 years ago (as the climate began to warm up) the ice melted and by 10,000 years ago it was all gone.

1.
In the high mountains of Britain we can see the effects of glaciers.  This is the Buttermere valley in the Lake District.  This valley would have been filled by ice.  The valley has been straightened and deepened by the erosion.  This type of valley is called a U-shaped valley.  

2.

Where the glacier moved across a ridge, it often stripped the soil and regolith to expose bare rock.  Sometimes these rock surfaces still show the scratch marks caused by the moving ice.  They are known as a 'roche moutonnée'.  This example is found in the Rhinog Mountains of NW Wales.

3.

Often the summit ridges of the mountains were exposed above the glacier.  The extremely cold conditions allowed water to penetrate the cracks in the rock, and frost to break up the rocks, leaving the slopes littered with jagged boulders of broken rock.  This view is on the famous Glyder ridge in Snowdonia.

4.

Not only were the valleys filled by glaciers, but also small glaciers formed on the sides of the mountain ridges.  These were called 'corrie glaciers'.  When the ice melted, the 'corries' had a characteristic curved shape (like an armchair) with a steep back-wall created by frost-shattering.  Often the floor of the corrie was hollowed, and would fill with melt-water to create what is known as a 'corrie lake' (or 'tarn' in the Lake District.)  This view shows the corrie which formed on the slopes of Snowdon in North Wales.  The cliffs are 400m high  above the lake surface.  How much rock has been eroded ?? 

5.

This corrie is in the Lake District, on the slopes of Grasmoor.  It was probably formed late in the ice age, because it has only been occupied by a small glacier.  You can clearly see the armchair-shape.

 

 

6.

In this view there is a corrie both to the left and to the right of the ridge.  As the glaciers eroded backwards towards each other they created a knife-edge ridge known as an 'arête'.  The arête in this view is called Crib Goch and is one of the ridges leading to the summit of Snowdon.  

7.
As the ice melted, new features were created by deposition of rock debris.  These boulders are different material to the rocks underneath and have been transported here from elsewhere.  They have been carried on the surface of a glacier and dumped high on the mountainside as the ice melted.  They are called 'erratic blocks'. This view was taken in Ennerdale in the Lake District.

8.
These hummocks are made of the clay and boulders which was been ground along under a glacier.  The ice smoothed out the material as it passed over.  When the ice melted they were exposed. These features are called 'drumlins'.  This view was taken in the Lake District near Langdale.
9.

The floor of the valley had often been hollowed out by glacial erosion, so that as the ice melted lakes were formed.  Sometimes the lakes have silted up, and elsewhere they are still open water.  These are the Elterwater lakes in Langdale in the Lake District.  How could you guess that these lakes are shallow ?

10.

Some of the lakes are very deep.  This is Wastwater in the south-west of the Lake District.     It is nearly 100m deep !  These long, thin lakes in glacial valleys are called 'ribbon lakes'

11.
Once the glacier has gone, the floor of the valley is usually covered with glacial debris called 'moraine'.  Sometimes the moraine is piled up as a ridge to mark the extent of the glacier at one time.  These moraines are called 'terminal moraines' because they mark the end ('snout') of the glacier.  You can see one on the mid-left of this view.

When the ice has gone, rivers take over the task of shaping the valley.  Here in Eskdale in the Lake District, we see a meander in the R. Esk.  These rivers smooth out the valley floor and have started the long task of levelling the valley floor and smoothing the long-profile.