glacio- fluvial depositions Flashcards
when are glacio fluvial processes are most evident?
When glacial periods end and when temperatures rise
what is iceland jokulhaups?
glacial outbursts caused by geothermal activity beneath glaciers caused melting→ lead to more than 200,000 tonnes of sediment deposited in valleys.
what are glacio - fluvial landforms?
Are created by meltwater from glaciers, largely through deposition but can be through erosion.
what is a subglacial stream?
They are streams that flow beneath a glacier which usually cuts into the ice above to form a tunnel.
Why may the energy of meltwater change ( 4 points) ?
- seasonal variation
- diurnal variation
- rapid drainage of englacial chamber
- blocking of a meltwater channel by ice
seasonal variation
loses energy in winter melts when the water in stream freezes so that discharges either are low or may cease altogether
diurnal variation
due to daily variation in ablation
Rapid drainage of englacial chamber
within the glacier a chamber of meltwater is rapidly drained → increasing velocity
Blocking of meltwater channel by ice
reduces speed / loses ability to transport material.
what does the Hjulstrom curve show?
Shows the relationship between river velocity ( y axis) and the size of the sediment (x axis)
Shows the relationship between river velocity and competence ( ability of a stream to transport individual particles of a given size)
As the sediment increases in size the :
- more deposition will occur more easily
- increased velocity required to transport material
- erosion requires increased energy within the water
what are glacio- fluvial deposits called?
outwash
characteristics of outwash
- smaller
- smooth and round
- sorted
- stratified vertically
characteristics of outwash
smaller
as meltwater streams are less energy than glaciers
characteristics of outwash
smooth and round
process of water and erosional attrition
characteristics of outwash
sorted
horizontally largest found in the valley and finer material further down the valley as velocity falls
characteristics of outwash
stratified vertically
vertically anually laid sediment following seasonal variations
How do characteristics of outwash vary?
Will vary from distance from the ice front in a series of zones
what are the three zones?
- proximal zone
- medial zone
- distal zone
Proximal zone
- larger particles
- reflecting high discharge of meltwater from the glacier
- As both direct glacial and meltwater deposition occurs * glacial till interbedded with glacio fluvial deposits
Medial zone
- not as coarse
- clasts are more rounded
- reflecting increase in transportation
- meltwater discharges are highly seasonally and daily variable
Distal zone
- better sorted
- more rounded
- only finer particles are transported this far - energy levels had fallen
