Glaciated upland landscapes

  ..... (glaciated upland = a mountainous area that has been eroded by ice).

Inhoud:

Glacial erosion landforms:
(landforms = landschapsvormen, terreinvormen)
.

1. Corrie / Cirque / Cwn ........................................... kaar (Nederlands)

2. Arête .......................................................................................... graat

3. Pyramidal peak / Horn ............................................ piramidale piek

4. U - shaped valley ............................ dal met U - vormig dwarsprofiel

5. Truncated spur .......................................................... afgeknot spoor

6. Hanging valley ............................................................... hangend dal

7. Ribbon lake .............................................................. langgerekt meer


1. Corrie / Cirque / Cwm.. kaar (Ned.) ... botn (Noors)

.... ( = a bowl-shaped hollow area formed by glaciation, sometimes
.......... containing lakes or tarns (corrie lochs).


Stage 1:
At the start of the Ice Age, snow collected in a hollow
( nis) high up in
the mountains and was gradually squeezed into ice.
As more and more snow built up, it filled the hollow and some of it was
then squeezed out and forced down the mountainside.
This was the starting point of a glacier.

.............................................................................................................................................

Stage 2:
The hollow in which the snow and ice collected was eroded by the ice
to form a much deeper, steeper hollow.
This is a corrie ( kaar).
As the meltwater under the ice seeped into cracks, the rock in the hol-
low was weathered by freeze-thaw action.

Then, when the meltwater froze onto the rock, plucking took place.
The back wall, sides and base of the hollow were eroded very quickly
by these two processes.
At the lip of the hollow the ice was less thick and so did less plucking.
But by now, there were fragments in the bottom of the glacier and so
the rock lip was abraded, making it smoother.

............................................................................................................................................

Stage 3:
When the ice finally melted at the end of the Ice Age, a corrie was
sometimes filled with meltwater
and so formed a
tarn (corrie loch)
.... kaarmeertje (Nederlands) .... botnsjø (Noors).
For example: Red Tarn on the eastern flank of Helvellyn.






2. Arête ..... graat (Ned.) ........ egg (Noors)
... ( = a sharp ridge of rock separating two corries).

On many mountains in Britain there is not just one hollow high up near
the summit, but several. So while a glacier was eroding a corrie on one
side of a mountain, the other sides would have other glaciers eroding
more corries.

Where two corries formed back to back or side by side, the rock be-
tween them was plucked away to form a sharp ridge, shown in figure
below.
This sharp ridge is called an arête
( graat).
For example: Striding Edge found on Helvellyn in the Lake District.


3. Pyramidal peak/Horn piramidale piek (pigg (Noors)
. (a sharply pointed mountain peak that has been formed by glaciation)

Where three or more corries formed back to back, the rock between
them was plucked and weathered into a sharp point called a
pyramidal peak
.

For example: Mont Blanc, The Matterhorn and Mount Everest..
Fig: Corries, arêtes and a pyramidal peak.


Red Tarn and Striding Edge, an easy arête.

 


4. U - shaped valley / Glacial trough
.... ( Letterlijk: U-vormig dal; ... beter: dal met U-vormig dwarsprofiel )
When a glacier was squeezed out of a corrie, it moved downhill under
gravity
.
It usually took the steepest route which, in most cases, was an old river
valley.
But the glacier was much more powerful than the river that was there
before, and it was able to completely change the shape and
appearance of this valley.

Before the Ice Age rivers in mountains ran down V- shaped valleys,
but when a glacier rumbled down the same valley the ice was so thick
that it was able to
pluck and abrade the valley sides as well as the
valley floor.

. ( plucking = a type of glacial erosion that occurs when ice freezes onto
.................... tthe landscape, ripping out rocks when it moves).

So the V- shaped valley became steeper and deeper and gradually
became a U - shaped valley, with very steep sides and a flat floor
(see figure).

Now that the ice has all gone, this U - shaped valley has a river flowing
through them again. But the river is too small for this very wide valley
and is called
misfit stream
( hongerrivier).
At the sides of the valley, scree
( puin) often builds up from all the
freeze-thaw weathering that has taken place on the valley sides above.
For example:
Great Langdale Valley in the Lake District.


..
Fig: The formation of a .. U - shaped valley.


Great Langdale Valley.

 

 

5. Truncated spur ...... afgeknot spoor (Ned.)
As it moved down the mountainside a glacier was strong enough to
keep a straight course. Instead of going around any obstruction, it went
over them, quickly eroding them away. Any spurs of rock that jutted
into the valley were eroded to become
truncated spurs
(= afgeknotte sporen).

6. Hanging valley with often a waterfall
.
(smaller valley which is located high above the main U-shaped valley)

Along its journey down the valley a glacier was joined by tributary
glaciers
(zijgletsjers).
These smaller tributary glaciers contained much less ice and so were
less powerful. They could not erode their valleys as deeply as the
main glacier so, where they met, the floor
(dalbodem) of the
tributary valley
(zijdal) is much higher than the floor of the main valley.
(The tributary valley was left 'hanging' above the main valley
(see figure below)

After the Ice Age, when rivers took over, the streams flowing from
hanging valleys often form waterfalls when they plunge into the main
(U-shaped) valley.


.
............. ( interlocking spurs = hills that a river meanders around in a V-shaped valley.
............... When viewed from downstream, these spurs appear to be locked together)

.
.
7. Ribbon lake
... langgerekt meer (Ned.)
...... ( = a long narrow lake found in a glacial trough).
...
At some points along the valley the glaciers were able to erode more
deeply than elsewhere. This might have been because the rock there
was softer and more easily plucked and abraded. it might have been
because the ice became thicker and therefore more powerful.
Wherever the ice did this, it made a hollow
( depressie) which, after
glaciation, became a lake.
The lake took on the same shape as the valley in which it was formed,
so it was long and narrow. It is usually called a ribbon lake
( langgerekt
meer).
When the ice reached warmer regions it melted and dropped all the
pieces of rock it had plucked and abraded. This material is called
moraine
(morene)
and often forms ridges
( wallen van morenemateriaal).
Sometimes these ridges did not allow the meltwater to escape and so
lakes built up behind them.
These moraine-dammed lakes are also examples of ribbon lakes.

Many of the lakes in the English Lake District are ribbon lakes, eg Windermere.

 


.

 

 

Location of glaciated uplands:
( glaciated upland = a mountainous area that has been eroded by ice )

There are four agents
(middelen) of erosion (wind, waves, rivers and
moving ice) and only moving ice does not affect the British Isles today.

Yet moving ice has had a huge effect on the shape of our landscape, so
we must study it in detail.

Our last Ice Age ended about 10,000 years ago. The ice was so power-
ful that it left behind striking landforms
( landschapsvormen ) that can
be clearly seen today.
This evidence of glaciation is most obvious when you look at our upland
areas
( hooglanden ).

During the depths of the Ice Age all of Britain, except the very far
south, was buried under slowly-moving ice-sheets
( ijskappen )
(see map below)
Only in our highest mountains did conditions allow glaciers to form and
move down the mountainside like a slowly-moving "river" of ice.
When they did this, the mountains never looked the same again
because the glaciers eroded them mercilessly
.

.Fig: Glaciated uplands ( vergletsjerde hooglanden ) in the Britsh Isles.
....... Ice covered land as far as the Bristol Channel. 

 


Two processes of glacial erosion:
.
Plucking ( = plukken):
Between a glacier and the rock underneath is a thin film of meltwater.
This water sometimes freezes, so the glacier becomes attached to the
rock.
Then, when the glacier moves forward, it pulls away any loose frag-
ments of rock. This powerful process is called
plucking
( plukken)
(It is highly likely that the rock will already have loose fragments
because of freeze-thaw weathering
. This is the weathering process
where water seeps into cracks
(scheuren), freezes and expands,
gradually wedging open cracks until the rock breaks.)

Abrasion ( = abrasie):
Once the glacier has plucked away pieces of rock, they become em-
bedded in the bottom of the glacier and scrape
( schuren) and smooth
( slijpen) the rock surface as the glacier moves.
This slower process of erosion is called abrasion
( abrasie).



Boek:

Nieuw venster National 4 & 5 Geography:
.
.. . Physical Environments 

.... Calvin Clarke and Susie Clarke, 2013
.... Hodder Gibson

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