Litoshpere Flashcards
when does Plucking occur
Plucking occurs when rocks and stones become frozen to the base or sides of the glacier and are plucked from the ground or rock face as the glacier moves downhill due to gravity. It cause the walls and surrounding rocks to become steeper.
when does Abrasion occur
Abrasion occurs when rocks and stones become embedded in the base and sides of the glacier. The rocks then rub along the floor of the glacier, like sandpaper, smoothing it as the glacier moves. This causes the surrounding rocks to become deeper and straighter/ smoother.
Freeze thaw weathering - formation of scree slopes
Rain enters cracks or joints in the rock and when the temperature drops to zero, the water freezes and expands by 10% putting pressure on the surround rock. When it melts, it stops exerting pressure. The constant freezing and thawing will eventually cause the rocks to break apart and shatter into pieces to form sharp angular shaped rocks which will fall to the bottom of the cliff / steep hillside to form scree at the base. Smaller rocks are found near the base of the cliff while the larger rocks gain more momentum and are found further away.
What is a Corrie and formation?
A corrie is an armchair shaped depression high in the hillside, normally facing North or East. For example Brown cove in the Lake District.
Before ice age
Snow collects in a hollow high in the hillside, normally facing north or east. Due to cold temperatures in Winter, more snow falls that is able to melt. Overtime it compacts tighter to form Neve ice and then into glacier ice.
During Ice Age
The glacier ice continues to compact together until the hollow is overflowing. This then causes the ice to rotate round the hollow and move downhill due to gravity, following the route of a persisting v-shaped valley. As the glacier moves, it does the following erosional processes.
Plucking - as the glacier moves downhill, the rocks which have frozen to the glacier get pulled out the wall and dragged downhill with the glacier. This causes the walls of the corrie to become steeper.
Abrasion - uses the plucked rocks and scraps them along the floor of the glacier like sandpaper, smoothing it as it goes. This makes the floor of the corrie deeper.
Freeze thaw weathering - happens above the glacier on the steep wall.s This creates the scree that is found along the lower parts of the wall when the glacier leaves the hollow.
After ice age
When the glacier leaves, the corrie is revealed. It looks like an armchair with the steep walls and a deep floor. In the floor of the corrie you may find a tarn - which is not left from the glacier. The corrie also has a lip at the front, this is where the glacier left.
What is the definition of an Arete and its formation?
An arete is a steep sided rocky ridge which separates two cores.
An arete is formed when a broad ridge between two cores is steeped and narrowed. The corries are enlarged through the processes of rotational slip, plucking and abrasion, and this backwards erosion causes the corrie back walls to retreat and the ridge to become steeper and narrower. Above the corrie glaciers there is severe frost shattering (freeze thaw weathering) in the very cold temperatures and this further stipends the ridge.
The arete ridge continues to be steepened by freeze-thaw weathering in post glacial times and the lower slopes will be scree covered.
What is a pyramidal peak
A pyramidal peak is a steep isolated summit, which is found where three of more aerates join together and it will be surrounded by three or more corrie back walls.
U shared valleys - what are they and how are they formed?
Before, during and after ice age.
U shaped valley, also known as glacial trough, is a wide, flat floored and steep sided valley which has been eroded by a valley glacier and resembles the letter “U”.
Before the ice Age
Pre glacial, the valley was a v-shaped valley which has been eroded by a river. The river runs around the interlocking spurs.
As temperatures continue to fall, the corrie glaciers grown larger and overflow to move downhill due to gravity. Ice from multiple corries join together to form a valley glacier which then follows the route down a pre- existing valley.
During Ice Age
The glacier bulldozes through the v- shaped valley making the interlocking spurs, truncated spurs. As the glacier moves the following erosional processes take place:
Plucking - Pulling rocks out of the side walls which makes the valley steeper.
Abrasions - uses the plucked rocks and scraps them along the floor of the glacier, like sandpaper, smoothing it as it goes. This makes the floor of the valley wider.
After ice age
When the glacier leaves the valley, the valley is now much straighter, steeper and wider than before and resembles the letter “U”. You may also find a misfit stream along the valley floor. Freeze thaw weathering leads to scree on the lower slopes of the u shaped valley due to the rocks breaking apart as the water expands, due to cold.
Where might you find a ribbon lake?
You may also find a ribbon lake along the floor of the u-shaped Valley. This is because part of the valley floor has been over deepened by erosion due to the soft rock eroding faster than the hard rock surrounding it.
Hanging Valley
What is a hanging valley?
How are they formed?
A hanging valley is a small glaciated u-shaped Vally which has its floor well above the floor of a larger u-shaped Valley. An example is glen einich in the cairngorm..
Before ice age
A tributary river in a tributary v-shaped Vally flowed into thew main river in the main v-shaped Valley without a drop in height.
During ice age
Both V-shaped become occupied by a glacier. The glacier erode the v-shaped valleys into u-shaped valley by the erosional processes.
Plucking - rocks being frozen to the glacier then being pulled out as the glacier moves downhill due to gravity. This makes the valleys steeper than before.
Abrasion - uses the plucked rocks / material and scraps them along floor of glacier. This makes the valleys wider.
After Ice Age
Both valleys are now much steeper, straighter, wider and deeper than before. However the main valley contained a much larger glacier so was eroded more rapidly so more plucking and abrasion took place. Where as the smaller tributary valley contained a smaller valley so was eroded more slowly = less erosion. When the glaciers left the valleys, the smaller tributory u shaped valley was help hanging higher about the main u-shaped valley. A misfit stream is normally found along both U-shaped valley and a waterfall drops from the mouth of the hanging valley to the floor of the main valley.
Glacial Deposition - what is drift?
Name given to material deposited by both ice and meltwater.
What is till (boulder clay)?
Material deposited by glaciers and ice sheets. It is unsorted and unstratified meaning that the material is all different sizes mixed together and not in layers. A glacier can’t sort material unlike a river which can. The larger particles are fairly angular.
Material transported by a river (or meltwater rivers) is sorted and stratified meaning the heavier materials are at the bottoms and the material is generally more rounded.
Terminal Moraines - what is it and how is it formed?
A terminal moraine is a ridge of unstratified till, mainly larger rocks, that crosses the valley floor and marks the furthest extent of glacial advance.
It is formed as a glacier moves along a valley it gathers much eroded material, which it transports down the valley. This material is a result from plucking, abrasion, freeze thaw weathering as well as other sources. The freeze thaw weathering above the ice contact zone causes scree to fall from the truncated spurs, that make up the valley sides, onto the surface of the glacier below. The moving ice then transports the supra glacial forward towards the snout of the glacier where the ice melts. Some of these rocks fall into crevasses and slowly work their at forward through cracks in the glacier. A final way is that rocks on the valley floor are pushed along or bulldozed by the snout of the glacier.
When temperatures were at their colder, the snout was at its furthest position down the Valley. Temperatures remained constantly very cold for several years and as the conveyor belt of ice moved to snot and melted, the material which has been carried forward was deposited. This formed a ridge of terminal moraine that crosses the valley floor.
Sometimes the terminal moraine acts as a dam and a ribbon lake may be formed behind it on the valley floor. The material deposited is unsorted as there has been little or no water present to carry and arrange it into stratified layers. This means that the erosion of water has not rounded the rocks.
Drumlins
What are drumlins?
A drumlin is a long oval hummock (small hill) of boulder clay found on the valley floor. They resemble half an egg cut along its side. They are formed parallel to the direction of ice movement. Drumlins have a steep by short side which faces the moving glacier, and a gentler but longer side.
Drumlins are found in groups called swarms.
There are patches of “dirty ice” at the base of the glaciers where the ice transports large concentrations of subglacial moraine. When the glacier or ice sheet melts and retreats, the material is then deposited to form unsorted mounds of angular till or boulder clay. Then when temperatures fall and the ice re-advances it moulds the boulder clay sub glacially into the distinctive elongated drumlin shapes.
The glacier may also deposit a bundle of till, but then forms the drumlins by eroding most of the till during a rapid re-advance.
What is a Esker?
Esker is a long, narrow, winding and steep sided ridges of stratified sands and gravels. They are made up of rocks and stones which have been sorted by water and they have been layered horizontally and arranged according to their size (stratified). They have been formed by water and ice so have been subject to attrition and eroded to become more rounder than the more angular moraine.
It marks the former coarse of a subglacial river and lies parallel to the direction of ice movement.
Subglacial meltwater rivers generally flow very rapidly through ice walled tunnels. The flow much to fast for deposition to occur as they are constrained by the small cross section area of the narrow tunnels. The water is forced through a small area so this is high pressure.
However as the ice sheet retreats the retreating ice walls start to melt and no longer place pressure on the water. Thus the river would slow down and deposits its load on the floor of the tunnel to form the long narrow esker ridge.
Seasonal variations in the rate of melting in the ice contract zone help to stratify the esker. More rapid summer melting increased the discharge of the subglacial river so that coarse gravels were deposited, but lower rates of melting in the winter led to the deposition of finer sands.
