Geography - Glaciation 1 (4th Form) (Formation of a corrie ( Picture1 ,…
Geography - Glaciation 1 (4th Form)
Ice Sheet/ Valley Glacier
Ice sheet is a very large glacier that covers a vast area. The key feature is that these ice sheets cover the top of the mountains. E.g. Antarctica.
Valley glaciers – These fill valleys that were at one time carved out by rivers. Places like Snowdonia and the Lake District were carved out by them. Still found in the Alps. Key is that they are held in place by the sides of the mountains.
Glacier Mass Balance
If accumulation is greater than ablation – the glacier gets bigger.
If ablation is greater than accumulation – the glacier gets smaller.
Material being lost is called ablation (melting).
Most glaciers have negative mass balance (getting smaller due to climate change)
Material being added to the glacier (snowfall) is called accumulation.
Glacial Erosion – Plucking and Abrasion
Abrasion – Sandpaper effect of the glacier. Rocks at the base of the glacier create striations on the bedrock.
Plucking – Water at the base of glacier freezes around the bed rock, becomes part of the glacier, and pulls out the rock.
Glacial Movement – Internal Deformation and Basal Sliding
Internal deformation happens when there is no water at the base. Instead, the weight of the glacier forces the particles to slide over each other.
Grade 9 information – Basal sliding happens in ‘warm based glaciers’ e.g. the Alps. Here, sufficient melting occurs to have water at the base of the glacier. In ‘cold based glaciers’ e.g. Antarctica, it is just too cold to have any meltwater.
Sides and top of the glacier may melt during the day – this water goes to the base of the glacier and helps the glacier move downhill. This is called basal sliding.
A glacier will drop its load when it loses energy: either moves to a flatter slope and so is not moving as quickly, or starts melting.
It will drop the largest particles first (need the most energy to be transported)
Glaciers carry particles (load) in a number of ways:
In the glacier itself
At the sides of the glacier
On top of the glacier
Deposited material is known as till.
Freeze Thaw Weathering – Link to erosion, rock fall and mass movement
When this rock breaks off – rock fall will occur – this is a mass movement process.
This process tends to happen at the sides of valleys. Rock may fall off and go underneath the glacier. Here, these rocks get dragged along by the glacier and are used as a ‘tool of abrasion’.
Freeze thaw – water enters cracks in the rock, freezes, expands by 9% of its volume and puts pressure on the rock. Many repeats and rock will break.
They make lines on rocks called striations.
Formation of a corrie
Corrie is a bowl shaped depression on the side of a mountain.
Formed by abrasion and plucking.
Glacier moves downslope, making the hole deeper.
Plucking works on the back wall and makes it steeper.
Rocks from the back wall may fall under the glacier and be used as a tool of abrasion.
Some rocks are deposited to form a rock lip and this acts a dam when the glacier melts and rainwater collects to form a tarn.
Formation of Aretes and Pyramidal Peaks
3 corries back to back – pyramidal peak.
When 2 corries go back to back into each other – arête is formed.
Glacier fills an old V shaped river valley. This valley will have interlocking spurs.
The glacier erodes the rock and produces truncated spurs where the interlocking spurs have broken away.
Freeze thaw weathering on the slopes above the glacier.
A river may run through the U shaped valley – this is known as a misfit river or misfit stream.
Plucking and abrasion here.
Ribbon lakes – long thin, glacial lakes. Found at the base of U shaped valleys. Areas of softer rock at the base of the valley are eroded more and produce lakes. Material is deposited at the end of the valley and dams to hold water in place.
Formed from plucking and abrasion
Key processes is regelation – this is the refreezing of meltwater and allows plucking to take place.
Formed of more resistant rock than surrounding rock
Found at the base of U shaped valleys