Glaciation Pack E Flashcards
What role does moving ice play in transforming the landscape?
It causes erosion and depositional landforms
What is weathering?
The breakdown or decay of rocks at the Earth’s surface creating regolith (broken up rocks)
What are the three types of weathering?
- Physical
- Chemical
- Biological
Which types of weathering are more common in cold places?
- Physical
- Chemical
How does freeze thaw weathering create debris?
- Water enters cracks or joints in the rock
- Water freezes in the joints and expands by up to 9%
- This wedges rocks apart and breaks them to form angular debris
What weather conditions are needed for freeze thaw weathering?
There must be frequent temperature fluctuations around the melting point, where temperatures must rise above melting point during the day and drop below freezing point at night
What about the landscape and rock type make freeze-thaw weathering more common?
- Jointed and permeable rocks
- Lots of water
- Frequent temperature fluctuations
What is erosion?
The wearing away and transport of rocks by ice and meltwater
What are the three types of erosion?
- Abrasion
- Plucking
- Meltwater erosion
What is abrasion?
The process where the material a glacier is carrying wears away the valley floor and sides
What is plucking?
When rocks and stones become frozen to the base of the glacier as water refreezes and are pulled from the ground or rock face as the glacier moves
How does abrasion work and what are the ideal conditions for it?
- Rocks scrape the bedrock as the ice moves
- In warm based glacier as there is meltwater
- Thick, fast moving glaciers with weak bedrock are ideal
How does plucking work and what are the ideal conditions for it?
- Joints are initially widened by fracture
- The large downwards pressure from the weight of the glacier and friction between the basal ice of the glacier and the rock below causes melting
- Water refreezes to obstacles
- Ice frozen to the valley sides moves
- Rocks are detached and chunks are removed from the bedrock and entrained in ice
- Highly jointed and permeable rock is best
What is subglacial meltwater erosion?
Erosional processes caused by meltwater running under the base of the glacier
Where does subglacial meltwater erode rock?
- Valley base and sides
- Snout (as there is more meltwater)
How does subglacial meltwater erosion erode rock?
Solution - where the meltwater dissolves minerals and carries them away
Hydraulic action - forces air and water into joints and pores which dislodges rock before it is taken away
Attrition - where material being carried hits each other
How is subglacial meltwater erosion powerful?
- Meltwater streams flow faster
- As they are under hydrostatic pressure from surrounding ice
- More erosive power
What is nivation?
The different processes that occur under snow (e.g. when freeze thaw and chemical weathering create material which is then flushed out by meltwater creating small nivation hollows which then form the start of a corrie)
What factors affect the rate of erosion?
Basal thermal regime:
- Warm based glaciers have increased erosion potential
- Pressure melting point has to be reached to provide meltwater for sliding
- Water must refreeze (regelation)
- Cold based glaciers protect underlying rock
Ice velocity:
- Faster moving glaciers are more erosive
- Pass over a larger area
Ice thickness:
- Thicker ice increases pressure and erosion potential
- More weight pressing on the underlying material makes abrasion more effective
Confluence:
- At a confluence more mass is added
- More erosion
Resistance of rock:
- Harder bedrock will erode less easily
- Harder rock entrained in the glacier will cause more erosion
Bedrock permeability:
- More permeable rock will erode more
- Water exerts pressure
Bedrock jointing:
- More plucking when more joints
Available debris:
- More weathered debris available leads to more erosion
Debris characteristics:
- Large, hard or angular rocks will cause more erosion
Topography:
- Steep mountainous areas lead to increased erosion
- More energy
Temporal control:
- More time that there is moving ice means more erosion
What is congelifraction?
Freeze thaw weathering that splits soil not rock
How is congelifraction different to freeze-thaw weathering?
Happens on the surface not under the glacier
What is fracture, traction and dilation?
- Fracture and traction happen as a result of the crushing effect of the weight of moving ice
- Dilation occurs as overlying material is moved so fractures in the rock are parallel to erosion surfaces
