Flashcards in Fluvioglacial processes Deck (28)
Why do fluvioglacial processes often transport a larger amount of material?
The meltwater has a large carrying capacity.
Flows under considerable pressure - high velocity - very turbulent.
Can pick up large amounts of material.
Responsible for the creation of subglacial valleys.
What is fluvioglacial deposited material like?
Stratified - vertical layering due to seasonal variations in sediment accumulation.
Sorted - larger rocks are deposited first as the melt water loses energy.
Material is smooth and rounded (due to attrition).
What are the main features produced by fluvioglacial deposition?
Outwash plains, Varves, Braided Streams, Eskers, Kames and Kame terraces, Kettle holes and proglacial lakes.
What are eskers?
Eskers are winding/sinuous ridges of stratified, coarse sands and gravels that are deposited by melt water.
Material is rounded due to water erosion.
5-20m for small eskers - up to 400km.
How are eskers formed?
Deposits made by subglacial streams.
The channel of the stream will be restricted by ice walls - hydrostatic pressure - enables a large load to be carried. Allows the stream to flow uphill for short distances.
Sinuous due to the stream finding the easiest route.
What is a beaded esker?
The ridge of an esker is combined with mounds of material (possibly kames).
In summer - more meltwater - more deposits.
What is an example of an esker?
Trim Esker, near Dublin.
What are kames?
Rounded mounds of fluvioglacial deposits.
Found near the end of the former glacier as it began to retreat.
Melt water held back by terminal moraine - lakes.
Deposited material where the melt water left the glaciers to flow into lakes – creating delta-like landforms.
If the ice retreats further, the delta kame often collapses.
What is an example of a kame?
Kingsdale Valley, Yorkshire Dales.
What are outwash plains/sandurs?
Areas that may have been glaciated by ice sheets and then affected by melt water.
Areas in front of the snout.
E.g. Greywake, Franz Joseph glacier
How are outwash plains/sandurs formed?
Melt water emerges from snout energy lost - no longer under hydrostatic pressure.
Material is deposited – the largest first -forms an alluvial fan at the end of the glacier.
Number of these merge – an outwash plain is formed.
The finest material is carried furthest, sorting the sediment by size.
Stratified due to annual flood events and meltwater high discharge.
What are some characteristics of an outwash plain/sandur?
Braided streams - highly variable discharge of the melt water streams - deposition - split into smaller streams.
Kettle holes - series of small depressions, filled with lakes or marshes.
What does an outwash plain look like?
Lateral erosion - flat.
Huge - many 10s of kilometres long and wide.
What is an example of an outwash plain?
Kankakee Outwash Plain, Indiana.
What is a braided stream?
Occurs on outwash plain/sandur.
Water loses energy - loss of the hydrostatic pressure - deposition occurs.
Deposition blocks off the water - creates distributaries.
Eyots form - vegetated on - become stabilised - bioconstruction.
What is a varve?
Bottom of proglacial lakes - shows distinct layering.
Layer of silt lying upon a layer of sand.
Shows one year of deposition in the lake.
The coarser lighter material represents the spring/summer deposition - meltwater at it's peak - maximum load.
The darker coloured finer silts are autumn/winter deposits - decreased discharge - fine sediment settles to the bottom of the lake.
What is a varve a good indicator of?
The age of lake sediments.
Past climates - the thickness of each varve represents warmer and colder time periods.
EXAMPLE: Alaska lake.
How are kettle holes formed?
Blocks of dead ice are washed onto the plain, melt, and leave a gap in the sediments.
Holes then fill with water to form small lakes.
Aquatic plants vegetate - marshy area over time, then peat.
What is a kame terrace?
Composed of sands and gravels.
Form along the glacier sides - not snout.
Ice marginal streams.
Valley walls warm up in summer - warm rock melts the ice nearest to it.
Sorted - main difference between a lateral moraine.
What is an overflow channel/meltwater channel?
Original river course before glaciation may be blocked by ice.
Lakes form on the edges of the ice.
Overflows from these lakes will then cross the lowest watershed points - forms new valleys.
When the ice damming the meltwater lakes completely melts, the drainage patterns revert to the preglacial stage.
What is an example of an overflow channel/meltwater channel?
The River Thames took a more northerly route before the Quaternary glaciation.
What is the preglacial stage of the River Severn?
STAGE 1 - OVERFLOW CHANNEL/MELTWATER CHANNEL CASE STUDY.
The River Severn flowed northwards to enter the Irish Sea.
The present Lower Severn was a shorter river flowing from the Welsh borderlands to the Bristol Channel.
What is the last ice age stage of the River Severn?
STAGE 2 - OVERFLOW CHANNEL/MELTWATER CHANNEL CASE STUDY.
Ice coming down from the north blocked the River Severn valley to the north.
The water from the blocked river formed a huge proglacial lake - LAKE LAPWORTH (reservoir).
The lake eventually overflowed the watershed to the south to join the original River Severn.
In the process it cut through a solid rock area, creating the gorge at Ironbridge (limestone).
What is the deglaciation and the postglacial stage of the River Severn?
STAGE 3 - OVERFLOW CHANNEL/MELTWATER CHANNEL CASE STUDY.
The ice retreated north, but the route north had been blocked with glacial deposits.
The Ironbridge Gorge had also been cut very deep.
The new drainage then adopted the new route rather than the former one - drainage diversion.
The River Severn now flows from central Wales to the Bristol Channel.
How is meltwater important?
Fluvioglacial landforms through erosion and deposition.
Highly dynamic and fluctuating environment.
How can water move through a glacier?
Supraglacial channels - ON.
Englacial channels - IN.
Subglacial channels - UNDER.
Moulin - water that flows on the surface and then enters an englacial channel.
How does discharge vary seasonally?
Summer - meltwater - high discharge.
Winter - may even stop if the temperature never rises from the PMP.
Varies on a daily basis - greatest discharges with the greatest daily temperatures.
Jökulhlaup events - extreme floods/discharge events.