Glacial Weathering and Erosion Flashcards
What is freeze-thaw weathering?
The physical force of water freezing in cracks in rock and expanding by 9%, wedging rocks apart to form angular debris. Needs to be frequent temperature fluctuations for this to be possible.
What are the main subglacial sources of material?
Material eroded form the glacier bed and valley walls. Also material frozen to the base from subglacial streams and englacial material.
What is the definition of glacial erosion?
The removal of material by ice and meltwater.
What is abrasion erosion?
Individual clast in the glacier base scrapes the rock as the glacier moves, forming striations and breaking some loose rock away.
What is plucking erosion?
Joints in the rock are pre-existing. Ice is frozen to the bedrock and valley sides, resulting in rocks pulled away and entrainment of loose material.
What is traction erosion?
The crushing effect of the weight of the glacier, with variations in the pressure melting point. This pressure leads to freeze-thaw of meltwater, breaking the basal rock apart.
What is dilation erosion?
As overlying ice moves, it causes fractions in the rock underneath due to the friction of subglacial rock and ice moving over it.
How is the glacier itself a factor affecting glacial erosion?
The size, thickness and thermal regime all increase the amount of meltwater and the PMP.
How does velocity affect the rate of glacial erosion?
A fast, thick glacier has the most power and therefore more violent erosion.
What are macro-scale erosion landforms?
Erosion landforms 1km2 +
What are the 4 macro-scale erosion landforms caused by glacial erosion?
Cirques, glacial troughs, hanging valleys and truncated spurs.
What are cirques and how do they form?
Snow accumulates in a small hollow. Nivation begins, enlarging the hollow through FTW and meltwater transporting debris away in summer.
Once a nivation hollow is established, it is a positive feedback loop where it traps more snow which then increases FTW and meltwater removal. Plucking and abrasion develop the cirques as the ice rotates vertically to develop it.
What are aretes or pyramidal peaks?
Aretes are where a cirque’s backwall extends back to the ridge, creating a knife-edged ridge across the top of it. A pyramidal peak has 3 cirques back to back.
What are glacial troughs?
When ice goes through a valley it goes from a V-shape to a parabolic U. They have a stepped profile which represents irregularities in erosion. After deglaciation, successive rock basis down a trough are separated by ridges. With sea level rise many were flooded and formed sea lochs.
What are hanging valleys?
When a small, shallow tributary glacier meets a valley glacier. During the glacier phase, the elevation of surface would be similar but they would have eroded vastly different depths. Once the glaciers have retreated, the side glacier is left hundreds of metres above ground.
