Glaciation Flashcards
Plucking
Glacial ice melts due to friction as it passes over an obstacle such as a large rock
This water will then almost instantly refreeze due to the overlying pressure of the ice
As it refreezes it gets into cracks and crevices in rocks in the ground and as the glacier advances, loose lives of rock are pulled or ripped out of the ground
Abrasion
This is when rocks that have been pulled out of the ground are now attached to the bottom of the glacier and they scour and scrape at the land below like sandpaper, wearing the land away, steepening and deepening it
Freeze-thaw weathering/frost shattering
Water collects in cracks and when it freezes, usually overnight, it expands by 9% putting extra pressure on surrounding rock
This repeated freeze-thaw action will weaken the rocks causing them to eventually break yo into large fragments
Fragments will move downhill by gravity and will accumulate at the base of a cliff as scree
Formation of a Corrie and tarn
When temperatures fall, there comes a time where last years snow will not melt. This is most likely to happen in north facing hollows as they receive less sunlight. As more snow falls on top the snow underneath gets compacted and all the air is pushed out causing it to turn into glacial ice known as nevee or firn.
As the mass of the ice increases its weight as well as gravity cause a rotary action which makes the ice rotate out of the hollow. This is called rotational slip.
As it moves, loose rock in the bottom of the hollow is pulled out, through a process called plucking. This is when glacial ice melts due to friction as it passes over an obstacle. The meltwater gets into cracks and crevices in the rock and then the meltwater quickly refreezes due to overlying pressure, as the glacier advances it pulls and rips out loose rocks from the ground.
At the back of the hollow a gap called a bergschrund, forms as ice pulls away. This gap allows melt water to get under the ice and therefore freeze-thaw weathering can take place.
This is when meltwater gets into cracks and as it refreezes it expands by 9% exerting extra pressure on surrounding rock. Over time a repeated freeze thaw action will cause the rock to weaken and break up into large fragments which often get embedded into the bottom of the ice.
The debris stuck to the bottom of the rock acts as a sandpaper and scrapes and scours at the ground below, wearing it away. This process it known as abrasion.
At the front of the follow, as the ice rotates out, it exerted less pressure and so a raised lip is formed. This lip can trap rainwater or meltwater forming a body of water known as a tarn.
For example red tarn in the Lake District
Formation of an arête
Corrie answer
When 2 or more carries form back to back they are separated by a knife edge ridge known as an arête
For example striding edge in the Lake District
Formation of a pyramidal peak
Corrie answer
When 3 carries form back to back around a mountain, they create a sharp pyramid shape and are separated by knife edged ridges known as arêtes
This is known as a pyramidal peak
For example helvellyn I’m the Lake District
Formation of a U-shaped valley
As temperatures fall, there will come a time where last years snow will not melt. This is most likely to happen in north facing hollows as they receive less sunlight. As more snow falls on top the snow underneath gets compacted and all the air is pushed out forming glacial ice known as nevee.
The weight of the glacier as well as gravity causes it to flow down down into an existing V-shaped valley.
As it moves it pulls out material from the valley sides. This is known as plucking which is when glacial ice melts due to friction as it passes over an obstacle. The meltwater gets into cracks and crevices and refreezes due to overlying pressure. As the glacier advances loose bits of rock are ripped out of the ground below and get embedded into the bottom of the glacier.
Material stuck to the bottom p of the rock act like a sandpaper and scrape and scour at the land below, wearing it away. This process is known as abrasion.
These processes deepen, steepen and straighten the valley.
Due to the force of the glacier, forming into locking spurs may be cut off leaving truncated spurs and steep valley sides. This is what turns the v-shaped valley into a u-shaped valley.
The width and shape of the valley depend on the nature of the rock type. A softer less resistant rock will erode more easily than a harder more resistant rock.
Tributary valleys have smaller less powerful glaciers which result in less deep U-shaped valleys that ‘hand’ above the main valley. These are known as hanging valleys.
Formation of a ribbon lake
A ribbon lake is a long narrow lake that sits at the bottom of a U-shaped valley
U shaped valley answer
When the glacier moves down through the valley is may reach as area of rock which is softer and less resistant meaning it is more easier eroded. This allows the glacier to gouge much deeper into the valley floor creating a long, narrow and deep area in the base of the valley
This is done through the process of abrasion
After the ice age, the melt water from glaciers and rain will fill up the basin in the valley floor, which creates the ribbon lake
Formation of a drumlin
Drumlins are elongated hills made up of unsourced glacial deposits such as till
Drumlins are formed when a glacier becomes overloaded with sediment and therefore deposits it, streamlining the sediment as it flows over it
It can also be created during a warmer period where the ice melts a little bit, depositing ground moraine carried beneath it. As it is still moving forward flowing downhill this shapes the moraine
Furthermore, if there is a small obstacle on the ground such as a resistant rock it will act as a trigger point and till from the glacial deposits can build up around it.
The steeper blunt end is known as the stows slope and faces up the valley on the direction the glacier came from. The more gently sloping end is known as the lee slope and faces down the valley.
Drumlins may be reshaped by further ice movements after being originally deposited.
They are found in swarms or in a ‘basket of eggs’ topography
Formation on an esker
Eskers are meandering ridges formed by meltwater streams in or underneath a glacier.
They are made up of meltwater that is fluvioglacial and deposits materials such as sand or small rocks.
These are sorted by size with larger stones at the base because larger stones are stoped first by flowing water.
The stones tend to be more rounded than unworried glacial deposits due to attrition. This is when rocks carried along in the water hit off and against each other causing bits to be chipped away and get more rounded.
Formation of terminal moraine
Terminal moraine is a ridge across the valley and is made up of glacial deposits which are unsourced. As the glacier moves downhill it acts like a bulldozer, pushing sediment in front of its snout as it goes.
On reaching lower altitudes the temperatures rise slightly causing the glacier to melt, lose its power and deposit the moraine its been pushing along.
‘Terminal’ moraine marks the furthest point a glacier reaches.
Once the ice has retreated, the terminal moraine can often form a natural dam created a moraine dammed lake. The glacier can move like a conveyer belt and if it stays in one place material can be moved to the front adding to the terminal moraine.
