GL 3 Flashcards
What is weathering?
Breakdown of rock, in situ
What are the two processes of weathering
Physical processes and chemical processes
What is erosion
Removal of rock by ice, water, wind or gravity
What are two types of weathering?
Freeze thaw / frost shattering, dilatation
Explain freeze thaw weathering
Water enters a crack in a rock, the temperature fluctuates on either side of 0 degrees Celsius. Water freezes and expands by 9% in volume. Putting pressure on rock, after repeated cycles the rock splits
What impacts freeze thaw weathering?
Geology of rock (more porous (absorption)/ bedding (gaps in formation)
Climate - temperature must be able to fluctuate between 0 degrees Celsius
Altitude - decrease in temp higher up
Aspect - Orientation of rock, North vs Southern hemisphere
What is an example of freeze thaw?
Summit of Glyder Fawr
Explain dilatation
Rocks fracture parralell to pressure when the pressure is released (glacier melts). Rocks expand and fracture fue to the pressure release. Called pressure relase or unloading.
What are three erosional processes?
Abrasion, Plucking, Sub-glacial meltwater erosion.
Explain abrasion
Weathered rocks are embedded as sub glacial debris (under glacier), this scrapes away at rock. Large pieces of rock cause scratches and striations, while fine particles cause smoothing an polishing (like sandpaper). When the debris gets worn away it turns into rock flour.
What are the factors effecting abrasion?
Ice thickness - thicker ice causes more erosion due to higher pressure, but too thick and the glacier becomes hard to move
Subglacial meltwater - Increases speed of glacier, but too much lubricant means the glacier will not erode
Relative hardness/resistance of debris and bedrock - if bedrock is harder there will be less erosion, weak debris turns into rock flour
Shape of debris - angular debris causes striations and cracks, fine sand and clay smooth and polish
Supply of debris - More debris causes more erosion, but it depends on the type of debris. Too much causes lower speed
Speed of glacier - Fast movement causes more erosion up to a point - too fast causes less erosion
Explain plucking
meltwater seeps into cracks in the rock, it refreezes, when the glacier moves to rock is plucked from the bedrock, causing the entrapment of rocks
What does plucking need to occour?
fractures in bedrock, resistant obstacles and meltwater
Plucking also occurs in what movement?
Regelation slip
What is sub glacier meltwater erosion?
Meltwater channels under glacier, high velocity causes erosion at the glacier’s bed and the widening and deepening of channels
What is an example of sub-glacial meltwater erosion?
Gwaun valley, North Pembrokeshire (South Wales)
How does sub-glacial meltwater occour?
Increase of meltwater in summer, water flows into cracks and forces rocks out (hydraulic action).
Rocks grind and scrape rock (abrasion)
Ricks bounce around, making them rounder (attrition)
Chemicals in rock release minerals (corrosion)
Lateral erosion and vertical erosion find path of least resistance
Why are sub-glacial meltwater channels powerful?
Ice adds pressure, increasing hydrostatic pressure and velocity
Why do sub-glacial meltwater channels have different discharge patterns to normal streams?
discharge comes from ablation in winter, movement is based on topography and movement of ice
What is a Macro landform?
What is a meso landform
What is a micro landform
Macro - big 1km+
Meso are often found in macro landforms
Micro are the smallest and often a few m
What is a cirque/cwm/corrie
Macro/Meso/Micro?
Case study
A large bowl shaped hollow, found at the head of a valley glacier.
Macro
Cwm coch
How many cirques surround the Nant Ffrancon valley? What direction do they face?
7, North east
How are cirques/cwm/corrie formed
on North facing slopes in winter, small hollows freeze thaw weathering occurs. in summer meltwater removes the debris, enlarging the hollow, called nivation. Firn compacts into ice.
Accumulation results in rotational movement of ice, meltwater from pressure melting adds to this effects, this movement causes stage 2.
Ice rotates, removing fragments from the back wall via plucking, causing a steep, jagged backwall. Rock fragments cause ablation on the hollows floor, deepening the corrie. Crevasses, called bergschrunds add meltwater, causing more rotational movement. Pressure release causes dilation cracks to form, weakening the floor of the glacier, aiding erosion. Glacier begins to moves over the lip of the corrie and out of the rock basin. with abrasion on the stoss side and plucking on the lee side.
What orientations are cirques. Why?
Northern hemisphere corries face north east. Receives the least amount of insolation (lower temperatures), meaning firn can form
