Unit 4a/4b Flashcards
What is extensional flow?
Ice that flows over an increasingly steep gradient will experience internal stress resulting in extensional flow.
Can result in supraglacial debris falling down crevasses and becoming englacial debris
What is compressional flow?
Ice that flows over a decreasing gradient will experience internal stress resulting in compressional flow which can result in sub or englacial material being moved towards the surface, becoming supraglacial debris
What debris is deposited directly by a glacier?
Glacial deposits
What debris is deposited by glacial meltwater?
Fluvio-glacial deposits
What is a lodgement till?
Forms subglacially and is ‘plastered’ onto underlying surface by the glacier
What is an Ablation Till?
Material is deposited from sub/en/supra glacial debris due to process of ablation
• Meltwater may remove finer particles leaving only larger ones
What is a Deformation Till?
If a glacier re-advanced over an area of previously deposited till, the underlying till sediment can be folded or faulted
What is a moraine?
An accumulation of glacial debris deposited by a glacier or left behind as the glacier retreated.
• Categorised between either subglacial or ice-marginal (formed on the edges)
What is a Till Plain?
Glacial moraines can cover large areas of land producing an extensive relatively flat area
• Typically have 50m thickness
What is a drumlin?
An elongated hill that is streamlined in the direction of ice flow
• 50m - 7km long
• Up to 100m high
• Form subglacially
• Process is called ‘Subglacial sediment deformation’
What are the theories of drumlin formations?
Fluvial theory
suggests that drumlin formation is due to meltwater
Deformational theory
suggests they are formed through a glacier moving over an obstacle and it gets plastered at the base
What are lateral and medial moraines?
Near the head of a valley, glaciers supraglacial debris is often concentrated in bands either at the sides of the glacier or the middle
side - Lateral
middle - Median
What are Terminal moraines?
These mark the furthest advance of a glacier
Debris is deposited at the furthest point which the glacier reaches
What is an esker?
Long winding ridges of sands, gravels and pebbles deposited by meltwater streams
What are kettle holes and kettle hole lakes?
Kettle holes are depressions found within the outwash plain located infront of a retreating glacier.
If it fills with water, it’s known as a kettle hole lake
