3. Fluvioglacial landscapes Flashcards
What are fluvioglacial landforms?
Landforms that are produced by meltwater from glaciers, that form during warmer seasonal periods or during deglaciation
What is a jokulhaulp + example?
An extreme glacial outburst caused by geothermal or volcanic activity beneath glaciers that causes sudden and massive melting
Eg 2010 eruption under Eyjafjallajokull ice cap led to surge of water though Markarfljot valley depositing 200,000 tonnes of sediment
Name 3 distinctive fluvial-glacial landforms:
Kames
Eskers
Outwash plains
What are the characteristics of outwash?
- Smaller than till as water has less energy than glaciers
- Smooth and round: subjected to erosion by meltwater
- Sorted: water deposits material based on size as the water loses energy
- Stratified: water sorts the outwash into layers
What is a kame?
A hill or hummock composed of stratified sand and gravel laid down by glacial meltwater
What are the two types of kame?
Delta kame
Kame terrace
Describe the ways in which delta kames form:
- En-glacial streams emerging at the snout of a glacier, losing energy at the base of the glacier and depositing its load
- Supra-glacial streams depositing material upon entering ice-marginal lakes and losing energy
- Debris-filled crevasses collapsing during ice retreat
What is a kame terrace?
A ridge of material running along the edge of the valley floor
How are kame terraces formed?
Supra-glacial streams on the edge of a glacier pick up later moraine which is later deposited on the valley floor as the glacier retreat
How do the supra-glacial streams, which create kame terraces, form?
They form due to the melting of ice in contact with the valley side as the result of friction and the heat-retaining properties of the valley-side slopes
What is the difference between kame terraces and lateral moraines?
Similar but kame terraces contain fluvioglacial deposits that are more rounded and sorted
Give an example of a kame terrace:
In the Kingsdale Valley of the Yorkshire Dales, a kame terrace extends for about 2km along the north side of the valley and is approx 2m high
What is an esker?
A long sinous ridge of stratified sand and gravel laid down by glacial meltwater
Eskers: When is material deposited in subglacial meltwater channels?
As the supply of meltwater decreases at the end of the glacial period
Eskers: When does deposition occur?
When the huge pressure inside the channel is released and meltwater emerged at the glacier snout
Eskers: Why does the point of deposition move backwards?
Because the glacier snout retreats
Eskers: What does it mean if an esker is beaded?
The ridge shows significant variation is height and width
Give an example of an esker:
Trim esker near Dublin is 14.5km long and 4-15m high
What is an outwash plain/sandur + example?
A flat expanse of sediment in the pro-glacial area
Eg Skeidarar Sandur, Iceland
How is an outwash plain formed?
As meltwater streams use energy in lowland areas, they deposit their load with the largest material deposited nearest the ice front and the smallest being deposited furthest away
What are outwash plains typically drained by?
Beaded streams
What are beaded streams?
River channels subdivided by numerous islets and channels
What does braiding begin with?
Begins with a mid-channel bar which grows downstream
How does a mid-channel bar grow and how does this cause braiding?
Discharge decreases after a flood or period of snow melt causing coarsest particles to be deposited first
Discharge continues to decrease so finer deposits added = increasing bar size
Channel bars are then colonised by vegetation at times of low discharge
River divides around the island and re-joins
What are the characteristics of unvegetated bars? + why are they common in outwash areas?
They lack stability and often move, forming and re-forming
They are common in outwash areas due to seasonal fluctuations
Give an example of a sandur:
South coast of Iceland is an extensive sandur fed by numerous meltwater streams = 5km
Why is it often difficult to identify fluvio-glacial deposits?
Repeated advance and retreat modifies the appearance of landforms + subject to weathering, erosion and colonisation by vegetation in post-glacial times
What happens to each of the three major fluvioglacial landforms as temperatures increase?
Outwash plains = greater accumulation as increased meltwater and exposed outwash material is colonised by lichens and mosses
Kames and eskers exposed in greater numbers and will become longer
