Glaciation Pack G Flashcards
How does material get into or onto a glacier?
- Ash from volcanic eruptions
- Landslides
- Lava flows
- Avalanches
- Plucking and freeze-thaw weathering
- Subglacial sediment lodging/getting stuck in ice
How does material become part of the glacier?
- Frozen to ice after regelation
- Incorporated as material is under the ice at the pressure melting point
- Subglacial bed deformation entrains material
How is material transported in and around glaciers?
Supraglacial transport:
- Debris from valley sides falls onto the glacier
- Frost shattered, avalanche and other debris falls onto the glacier
- Material is angular and unsorted as hasn’t undergone abrasion
- Only happens on constrained ice masses
Englacial transport:
- Debris falls into crevasses and is moved within the glacier
- Occurs when the ice moves differentially and forms crevasses
Subglacial transport
- Basal ice freezes around the material and drags it along by traction
- Material is plucked from the bedrock through pressure melting and regelation
- Small fragments are entrained by basal ice and dragged along
- Large boulders may be enveloped through deformation flow
- Occur on all ice masses
What factors affect the amount of debris being transported?
More debris is transported when…
- Densely jointed rock in valley
- High rates of weathering
- Glaciers converge
- Steep gradient of slope above
- Unvegetated slopes
- Fast streams
- Near the snout
How can debris move from one part of a glacier to another?
- Englacial to supraglacial happens if the surface of the glacier melts
- Subglacial to englacial happens with ice movement
- Meltwater moves material which then may become frozen into the ice
Where is the most debris found and why?
- In the ablation zone
- Due to the conveyor belt like nature of the glacier
- Least energy
- End of glacier so there has been time and distance for more material to accumulat
What are erratics?
A rock or boulder that differs from the surrounding rock and is believed to have been brought from a distance by glacial transportation
How is an erratic formed?
The rock has been moved by the glacier
What is an example of an erratic?
Bowder Stone, Lake Distric
What factors affect the speed the material moves at?
Basal thermal regime:
- Warm based glaciers move faster
Ice velocity:
- Speed of the glacier is the speed that the debris will move at
- Faster glacier = faster speed of material
Gradient of the valley:
- Steeper valleys allow glaciers to move faster
Amount of meltwater:
- More meltwater means more material can be carried faster
Lithology:
- Smooth rock creates less friction so glacier and material flows faster
Mass balance:
- High rates of accumulation and ablation mean that the glacier will move more
Mass of a glacier:
- Large glacier will move faster due to gravity
How does the transport process affect the sediment type?
- Glacial transport creates angular rocks
- Fluvioglacial transport creates rounded rocks
Where and when is material deposited?
- Most will be debris released at the glacier’s snout due to the melting of the ice
- If the ice becomes overloaded, its capacity to transport material will be reduced
What is till?
Any unsorted mixture of rocks, clay and sand that was mainly transported on/in/under the glacier and was deposited when the ice melts
What does till tell us?
It reflects the character of the land over which the ice has passed so can tell us the direction of ice flow
E.g. East Anglian till contains granite from Norway, telling us the direction of ice flow was SW
How is material moved in meltwater streams (fluvioglacial transport)?
Solution:
- Minerals are dissolved in the meltwater
Suspension:
- Fine, light material is carried along by the meltwater
Saltation:
- Small pebbles and stones are bounced along the bedrock
Traction:
- Large boulders and rocks are rolled along the bedrock
