Glacia and Fluvioglacial Processes and the Formation of Associated Features Flashcards
What is the process of lodgement?
Occurs beneath the ice mass when sub-glacial debris becomes stuck on the glacier bed. This occurs when the friction is greater than the drag from the glacier
What is the process of Ablation deposition?
Dumping of debris as the glacier thaws and melts
What is the process of deformation deposition?
Less common and associated with weak bedrock. The sediment beneath the glacier is deformed by and broken apart by glacier movement
What is the process of glacial flow deposition
Occurs if high meltwater causes the debris to creep, slide or flow
What are the characteristics of Lodgement till?
Rounded clast, often a matrix of clay or silt.
Forms till sheets and drumlins.
Oriented with the direction of glacier movement.
What are the characteristics of ablation till?
Angular and longer .
Unsorted - no orientation
What are characteristics of Modified till?
Reworked older deposits - have folds and faults in.
Forms ridges or thin sheets
What is fabric analysis?
Analysis on till to understand what type of deposition caused it
Generally, how is glacial till deposited?
Unstratified, angular and unsorted.
Where can you find moraines?
Sub-glacial or ice-marginal.
What is a till plain?
Extensive flat areas of till that cover pre-existing topography up, up to 50m deep. Formed by consistent ablation till dropped as the glacier advances.
What are drumlins?
10-50m high, 200-2000km long. The stoss is end up-glacier then sweeps down. Found in lowland areas, and in relatively close proximity to upland centres of ice dispersal.
What is the Boulton-Menzies explanation for drumlin formation?
Drumlins are formed by deposition in the lee of a slow-moving obstacle in the deforming layer. The obstacle forms the rock core of the drumlin and moraine is plastered around it.
What is the Shaw theory for drumlin formation?
All drumlins are caused by subglacial meltwater in flood, causing irregularities in the bed - formed into drumlins by ice movement. This more explains smaller drumlins.
What are the two main sources of meltwater?
Meltwater and basal melting.
What are moulins?
A small hole that goes directly down through the ice, formed often by debris on the surface which has melted its way into the ice. Supraglacial streams can seep through it to become englacial or subglacial streams.
Where do meltwater streams emerge?
At the snout, through caves called portals.
What are the characteristics of fluvioglacial deposits?
Generally smaller as streams can’t carry large till.
Smoother and rounder due to attrition.
Sorted horizontally, larger pieces up-glacier as they require more energy to transport.
Vertically stratified.
What is the proximal zone?
Directly ahead of the snout. Largest particle deposits such as moraines.
What is the Medial zone?
Further from the ice margin. Meltwater streams often form braided channels here.
What is the Distal zone>
Furthest from ice margin. Drainage pattern meanders on flood plain.
What are eskers?
Long, sinuous ridges of sand and gravel deposited by meltwater tunnels. They can become beaded eskers if there are buildups of sediment in areas where the tunnels were blocked for a period.
How are eskers formed?
Through subglacial meltwater deposition - when meltwater streams deposit sediment due to the stream being blocked. Another method is when a delta of fluvioglacial material extend outward perpendicular to the ice margin.
What is a kame and how is it formed?
A steep-sided conical hill. They are formed by deposition of material in ice in surface depressions or crevasses. These erode their way down through the ice and are deposited at the base as kames. They show evidence of stratification but the bedding can be disturbed by meltwater streams.
What is a kame terrace and how is it formed?
Relatively continuous bench-like features along valley side. Formed when a gap between valley side and ice is filled with fluvioglacial deposits.
What is an outwash plain?
A gently sloping surface of rounded, sorted and stratified sands and gravels with partial size becoming smaller as the meltwater loses energy. They are formed by a stream rapidly exiting the snout, depositing material. The braided drainage channels can continue to deposit.
What are kettle holes?
They form in outwash plains where ice was buried beneath gravels or sands. After the ice melted, the ground fell in to form a depression. These fill with water and undergo succession to become a hydrosere. They can be between 400 and 1500 metres in diameter and form lakes
What is a proglacial lake?
Meltwater exiting becomes impounded within a depression blocked by ice and high ground. They are temporary and could empty rapidly during deglaciation.
What are strand lines?
They occur when water was stationary for a long time - sediment deposited at the edges of a lake as it was fed by meltwater.
What are varves?
Deposits at the bottom of a proglacial lake. There are alternating bands of sand overlain by dark-coloured silt/clay. These bands reflect the amount of annual discharge.
What are overflow channels?
Formed when proglacial lakes overflow. They are an open V-shape often gorge-like and sinuous. These are caused by intense fluvial erosion as the overflow erodes a channel out of the like. Many are now dried up after the lake drained away during deglaciation.
