3.1.4.4 Fluvioglacial Landforms Flashcards
What is produced when glaciers melt to transport a lot of debris
Huge quantities of meltwater
What are meltwater streams like
Often flow under pressure so have high velocity + turbulent flow.
Can pick up + transport a larger amount of material than normal rivers can
What causes meltwater to deposit material
What’s this material like when it’s deposited
It’s discharge decreasing causing energy loss
Heavier particles are dropped first so material is sorted. Can also be found in layers due to seasonal variations in meltwater flow
Describe a fluvioglacial landscape
- Meltwater
- wide multi-channelled (braided) river flowing over a vast area of 2 types of sediment
- very dynamic landscapes with river channels migrating + changing course
2 types of sediment in a fluvioglacial landscape
Poorly sorted angular glacial till
Well sorted more rounded out wash (sandy/gravelly)
2 fluvioglacial landforms due to erosion
Meltwater channels
Proglacial lakes + overflow channels
Describe meltwater channels
When glacial ice melts, it’s water forms streams of meltwater
It flows through tunnels underneath the glacier before running out of the snout
Why do meltwater streams cause more erosion than rivers
4 types of erosion
Due to the ice’s pressure causing meltwater to flow very quickly
Abrasion
Attrition
Solution
Hydraulic action
How do meltwater channels form
Meltwater streams form deep troughs in the landscape called meltwater channels.
As meltwater streams have a lot of erosive power, the meltwater channels produced are very wide + deep
Describe proglacial lakes + overflow channels
During deglaciation, lakes develop on edges of ice, some occupying large areas
Overflows that cross lowest points for the watersheds will create new valleys
When the ice dimming these meltwater lakes melts, many new valleys are left dry
What was the huge proglacial lake formed as ice blocked the River Severn valley
Lake lapworth
How did the river Severn and lower Severn form one
What did it form in the process
Lake lapworth eventually overflowed the water shed to the south to join the lower Severn and when it retreated back north, the route was blocked by glacial deposits
Formed a gorge in the process
4 fluvioglacial landforms due to deposition
Eskers
Kames
Kettle holes
Outwash plains (sandur)
What are eskers
Long sinuous (winding) ridges of material running in direction of ice advance 5-20m high
What do eskers consist of
Sorted coarse material (coarse sands and gravel)
How do eskers form
Stream’s channel is restricted by ice walls causing hydrostatic pressure allowing a large load to be carried
Load builds up the bed of the channel above surrounding land/close to the snout the hydrostatic pressure may drop leading to deposition
When is a ridge left during esker formation
When the glacier retreats during deglaciation
What are kames
Mounds of fluvioglacial material
Deltaic deposits left when meltwater flows into a lake dammed up in front of the glacial snout by recessional moraine deposits
What are the 3 types of kame
Kame terrace
Kame delta
Crevasse kame
What’s a kame terrace
Most extensive kame
Results from infilling of a marginal glacial lake
When ice melts the kame terrace is abandoned as a ridge of valley side
What’s a kame delta
Smaller feature that forms when a stream deposits material on entering a marginal lake
They form small,mound-like hills on the valley floor + can be identified by deltaic sedimentation characteristics
What’s a crevasse kame
Kame resulting from fluvial deposition of sediments in surface crevasses
When ice melts they’re deposited on valley floor to form small hummocks
What’s a kettle hole
Depression in a glaciated lowland area that usually contains a small lake
How do kettle holes form
Results from blocks of ice that get detached from the icefront as the glacier retreats
These blocks get covered in glacial + fluvioglacial debris and slowly melt
As they disappear a hollow is produced on the site which later fills with water
What’s an outwash plain (sandur)
An extensive, gently sloping area of sands + gravel formed in front of a glacier
How are outwash plains (sandur) formed
Result from outwash of material carried by meltwater streams + rivers. At the end of a glacial period, huge quantities of meltwater will be spread out over the outwash plain.
What season are more outwash plains formed
Summer (more melting)
What distance are the coarsest material and finest material (clay) found at in outwash plains
Coarsest - travels shortest distance so is found near to glacier
Finest - carrier further across the plain before being deposited
