EQ3 - How Do Glacial Processes Contribute To The Formation Of Glaciated Landscapes And Landforms Flashcards
Explain the glacial process of freeze thaw weathering and how it creates distinctive landforms
Water enters the cracks and freezes
The water melts and then refreezes, causing pressure to increase
Cracks increase in size and expand
Rocks cracks expand so much that rocks break off
Explain the glacial process of plucking and how it creates distinctive landforms
Meltwater is present at the base of the glacier due to pressure melting
The meltwater penetrates into joints and freezes onto rock
As ice moves it exerts an immense pulling force onto the attached rock
The rock is fractured and plucked from its position, leaving a very jagged landscape
Explain the glacial process of glacial abrasion and how it creates distinctive landforms
As the glacier moves downslope material rubs against the valley sides and floor
Rock debris scratches the surface , leaving striations and polished flour rock
Rates of abrasion are highest when the rock is fast moving
Explain the glacial process of glacial crushing and how it creates distinctive landforms
Is the direct fracturing of weak bedrock by the weight above it
The bedrock is first weakened by freeze thaw weathering or dilation
Bedrock crushing produces large angular blocks of rock
Explain the glacial process of fluvio-glacial erosion and how it creates distinctive landforms
Basal ice melting beneath temperate glaciers produces meltwater
Causes the process of abrasion, hydraulic action , attrition and corrosion
Explain how a corrie is formed (3 stages) (erosional process)
Draw it out
Beginning of a corrie - face north east , away from the sun, allowing accumulation. Alimentation occurs where snow is compressed into ice. Nivation and freeze thaw weathering increase the size of the hollow
During ice age - glacier gets bigger as it moves downslope , rotational slip (circular motion) occurs to form a deep shaped hollow. Plucking forms a craggy backwall and a rock lip is formed. Raised lip causes deposition to occur forming a moraine
After ice age - ice melts and water gets trapped behind the lip creating a tarn . Back wall is weathered by freeze thaw producing a scree.
Leaves a jagged summit with a deep rock basin
Define alimentation
Occurs when accumulation compresses snow to turn it into tarn and then ice
Explain how an arête is formed (erosional process)
Draw it out
Snow gathers into two hollows back to back, alimentation takes place to turn it into ice
Glaciers either sude if the arête move downhill eroding the surface as they go. Rocks are plucked from the back wall
Freeze thaw weathering leaves a knife edged ridge between two corries
Explain how a pyramidal peak is formed (erosional process)
Draw it out
Snow gathers in three or more hollows back to back, alimentation occurs turning it into ice
Glaciers move downhill, eroding as they go and rocks are plucked from the backwall
Freeze thaw weathering leaves a pyramidal peak with three or more corries on the sides of the pyramid
Explain the process leading to the formation of glacial troughs
(Erosional process)
Occurs where a glacier moves through a mountain valley, eroding the sides and base to make it wider and deeper, to make the valley u-shaped with a flat base
Explain the process leading to the formation of truncated spurs
(Erosional Process)
Usually the river flows around the interlocking spur . When ice occupies the valley, the glacier cuts off (truncates) the tips of rocky spurs as it moves downhill.
Abrasion , plucking , freeze-thaw and rockfalls causes this
Explain the process leading to the formation of hanging valleys
(Erosional Process)
Occur when a small tributary glacier meets a large main valley glacier .
The small glacier has less mass and erosive power meaning it is left hanging over the main valley
Explain the process leading to the formation of ribbon lakes
Erosional process
Are a long, narrow lake along the floor of the glacial trough .
Caused by enhanced erosion, forming in a hollow due to the glacier eroding less resistant rock.
What are the landforms associated with cirque and valley glaciers caused by erosional processes
Corries Arêtes Pyramidal Peak Glacial Trough Truncated spurs Hanging valley Ribbon Lake
Explain the ice contact depositional feature of a lateral moraine
Where exposed rock on the valley side is weathered and fragments fall down onto the edge of the glacier through mass movement.
Deposits angular morainic material at the side of the valley, parallel to ice flow
Explain the ice contact depositional feature of a medial moraine
When two glaciers meet the lateral moraines join together to form a medial moraine.
Angular morainic material is deposited in the middle of the valley, parallel to ice movement.
Explain the ice contact depositional feature of a terminal moraine
Where advancing ice carries the moraine forward and deposits it at the point of maximum advance when it retreats
The up valley side is steeper than the other side
Its transverse to ice flow
Explain the ice contact depositional feature of a recessional moraine
They occur when a glacier retreats and deposits material transverse to ice flow
Good indicator of the cycle of advance and retreat that glaciers suffer
Explain the ice contact depositional feature of Drumlins
What are the two theories , issues ?
Are smooth elongated mounds of till, parallel to the direction of ice movement with a steep stoss and gentle lee. Found in large numbers called drumlin swarms
The Boulton menzies theory - drumlins are formed by deposition in the lee of a slowly moving obstacle
The Shaw theory - formed by subglacial meltwater irregularities in the river bed
What are the ice contact depositional features needed
Lateral Moraines Medial Moraines Terminal Moraines Recessional Moraines Drumlins
Define Ice extent
Define Ice movement
Extent is the distribution of landforms, size of landforms and maximum extent
Movement is the direction and velocity of ice movement
How can corries be used to reconstruct past ice extent and movement
Issues?
Cannot be used accurately to reconstruct ice extent
Can be used to measure ice movement , usually facing north east to show the direction of movement. As the glacier moves it turns larger till rock in the direction of ice movement
Its issues for reconstructing is that there will always be anomalies of the direction the corrie faces, a large sample size is needed
How can Glacial Troughs be used to reconstruct past ice extent and movement
Issues?
For extent, it is possible to identify a trimline to indicate the height and extent to which the glacial trough was filled with ice
Cannot be used to show past ice movement and overall direction of the glacier
Issues are that weathering since the glacial period has occurred, reducing the accuracy of the trimline overall
How can Roche Mountonnee be used to reconstruct past ice extent and movement
Issues?
Cannot be used to measure ice extent as the rock was there before the landform , the glacier moved around it
Can be used to measure ice movement. Striations show ice movement parallel to the rock. Stoss end shows the direction the ice was coming from , lee shows direction the ice was moving in
A glacier can become so big that the ice movement may only show localised glacier movement rather than the whole glaciet
How can a Crag and Tail be used to reconstruct past ice extent and movement
Issues?
Cannot be used to measure ice extent because ice regelates and moves around the landform
Can be used to measure ice movement as the tail is showing the direction the ice is moving in
Glacier can become so big that the localised direction of movement is different to the overall path of the glacier. Also weathering could have modified the landform
Define an erratic
Is a rock fragment deposited far from its origin , can be used to recreate paleo-environments (fossil or past environments)
Explain a till plain and how it creates lowland depositional movement
Till plains are created by ice retreat where the ice sheet retreats leading to a large amount of material being deposited due to melting. Leaves a large, flat plain of till in a lowland area.
Explain Ablation Till and how it creates a lowland depositional landform
Ablation Till is created by ice retreat due to ice melting from retreating glaciers.
Material is deposited to form terminal and recessional moraines.
Also leaves deposits of angular rock which is unstratified and contains erratics
Explain Lodgement Till and how it creates lowland depositional landforms
Formed due to active glacial movement where till is deposited to form drumlins, pressed into the valley floor beneath the glacier. Leaves angular rock which is unstratified with mixed geology
How can Ground Moraine be used to reconstruct past ice extent and movement
Issues?
If distribution of ground moraines is spread over a large area it is a large glacier
As the glacier moves , till fabric analysis can be used to work out the origin of the rock and its axis shows the direction of movement
12,000 years old meaning that it has been modified by weathering and human activity
How can Terminal Moraines be used to reconstruct past ice extent and movement
Issues?
Deposition occurs at the snout of the glacier, maximum advance, showing the extent of the glacier
Upvalley side is steeper than other side showing direction of movement
Can be altered, modified or destroyed by later glaciations
How can Drumlins be used to reconstruct past ice extent and movement
Issues?
Distribution of drumlins can be used to show extent
Boulhon theory shows direction of ice movement over the lee. The elongation ratio can be used, increases with movement
Equifinality means we are not sure how drumlins are formed so cannot be accurately used to reflect past ice movement and extent
How can erratics be used to show past ice extent and movement
Issues?
Cannot be used to show full ice extent, can show that glacier was huge in size due to the size of the erratics that it carried
Can be used to show ice movement , has the ability to transport enormous quantities of rock over a large distance
Issues is that we are not sure of the full direction of the glacier
What are fluvio- glacial landscapes
What are the two types
Are landscapes created by meltwater in glacial or periglacial environments
Two types : Ice contact features , Pro-glacial features
Define the fluvio- glacial landforms of Kames
Are ice contact features formed on the ice surface. They consist of sand and gravel deposited by streams in the final stages of a glacial period
Explain the three types of Kames
Kame terraces - result from filling of the marginal lake , left as a ridge on the valley side
Kame Deltas - form when a stream deposits material on a marginal lake, leaving small , mound hills on the valley floor
Crevasse Kames - small hummocks deposited on the valley floor due to sediment deposited in creavasses
Define the fluvio-glacial landforms of Eskers
Are ice contact features formed when subglacial streams carry large amounts of rock debris. Streams meander beneath the glacier leaving a long narrow ridge when the glacier retreats.
Define the fluvio-glacial landforms of pro-glacial lake
Is a pro-glacial feature. Is a lake at a glacier snout formed by the damming action of a terminal or recessional moraine during glacial retreat or due to meltwater being trapped against an ice sheet
Define the fluvio-glacial landform of kettle holes
Is a proglacial feature which forms a lake in an outwash plain. Occurs when the glacier retreats, detached blocks of ice remain. Meltwater streams flow over ice , eventually the ice melts to form a depression which fills with meltwater to form a kettle hole lake
Define the fluvio-glacial landform of a outwash plain
Are proglacial features which are gentle sloping plains of sand or gravel that are sorted and stratified. The gravel is deposited first and then sands are carried further down the plain. This occur due to the meltwater stream losing its energy.
Define the fluvio-glacial landform of meltwater streams
Are proglacial features where narrow channels cut into the bedrock. Occurs when meltwater erodes deep into channels due to hydrostatic pressure and their high sediment load.
How can kames be used to show past ice extent and movement
Issues?
Not used for extent.
For movement, kame terraces are formed at the ice margins and are parallel to ice flow
Will only show localised direction as the marginal lake does not follow the whole length of the glacier. Can also be modified by weathering.
How can Eskers be used to show past ice extent and movement
Not used for extent
For movement , they are formed englacially and sub glacially so can indicate areas of ice cover. Indicates direction assuming meltwater and ice flowed in similar directions, theton esker in Canada (800km) .
ASSUMES ice and meltwater flowed in the same direction, not 100% accurate
How can outwash plains be used to show past ice extent and movement
Issues?
For extent , Large ice sheets have a sandur in front of the ice which consists of meltwater channels. The edge of the sandur can be used to infer the edge of the ice.
Not used for movement
Issues, tectonic activity and glacial outbursts in Iceland can modify Sandurs , not accurately used
How can meltwater channels be used to show past ice extent and movement
Issues?
Not used for extent
Meltwater channels are parallel to the direction of ice flow.
ASSUMES direction is parallel
What are the characteristics of fluvio-glacial deposits
Generally smaller than glacier till due to having less energy
Smoother and rounder through attrition
Sorted horizontally , largest material near glacial snout
Stratified vertically with distinctive layers
Explain the glacial and fluvio-glacial deposits of stratification
Occurs where deposits are layered, rock fragments are graded by seasonal variation with finer sediment deposited in the summer and coarse sediment in the winter.
Explain the glacial and fluvio-glacial deposits of grading
Occurs due to change in rock fragment shape (attrition) . There is coarse sediment at the base and finer sediment at the surface.
Explain the glacial and fluvio-glacial deposits of sorting
Involves the seasonal variation in discharge sorting grains into layers of consistent size.
Explain the glacial and fluvio-glacial deposit of imbrication
Occurs when rock fragments have a preferred orientation and align with the direction of flow
