Glaciation - lithosphere Flashcards
(35 cards)
Formation processes:
Abrasion and Plucking
Abrasion
a sand-papering effect as the ice moves across the land
produces smoothed surfaces
rocks embedded in the ice
scrape along the ground
Plucking
Pieces of rock are torn away from the land
produces jagged features
ice freezes around rocks
rocks pulled along with gravity
Fluvioglacial
as glaciers move they erode and deposit material at their margins; the front and sides. Meltwater flowing from the glaciers further erodes and deposits material in processes
Stages of glaciation (3)
- stage 1: snow falls and begins to accumulate; it has an ice crystal lattice structure and spaces are filled with air; giving a “fluffy” texture.
- stage 2: snow becomes partly melted (ablation). Melt water seeps downwards then freezes at a deeper level. The snow compacts due to it’s crystals collapsing and expelling air. The layer now has a granular appearance called Névé.
- stage 3: Névé becomes buried beneath new snow (firn); found below the level where ablation occurs in névé. Continues to become compact and more air squeezed out. This makes it slightly denser than névé while maintaining it’s granular consistency in a manner often described as wet sugar .
Zone of accumulation
accumulation exceeds ablation/melting
Zone of ablation
ablation/melting exceeds accumulation
Equilibrium
accumulation equals ablation/melting
Continual glaciers
slow moving, continuous sheets or layers of ice that cover extensive areas over a large period of time
e.g Antarctica and Greenland
ice-caps
where smaller areas are covered
e.g Cuillin mountains in Skye during the Loch Lomond stadial
Input of a glacial system:
1- snow (precipitation)
2- snow from avalanches are blown from surrounding area
3- condensation of atmospheric water vapour which freezes
4- sublimation of atmospheric water vapour to ice crystals
5- rock collected by glacial movements (plucking) carving the landscape
6- rocks and rock fragments that fall onto the glacier from above (as part of avalanches or due to weathering and erosion)
Outputs of a glacial system:
1- ice melt (meltwater)
2- ice and snow sublimating to water vapour
3- surface snowmelt or evaporation
4- surface snow blown off the glacier
5- the calving of icebergs if the snout of the glacier extrudes into water (ocean, sea, loch/lakes)
6- rock debris (sand, gravel, rock (numerous sizes)) deposited by melt water
7- rock debris deposited as the glacier retreats (moraine)
conditions needed for Glaciation
winter conditions with low temperatures and heavy snowfall; and low summer temperatures
piedmont glaciers:
glaciers which upon reaching the foot of a glacial region spread out onto flat ground
ice-shelves:
when in similar circumstances as the piedmont glacier, the glacier spreads out onto the ocean
freeze-thaw or frost-shattering:
- in areas of bare rock where temperatures are 0
- water gets into cracks
- freezes (overnight)
- expands by 9%
- melts
- repeated process
- rocks break off; scree
scree
- masses of such angular rock waste often accumulate below cliffs and mountains
corrie basin
bowl shaped hallows found in mountainsides, formed by glacial erosion.
Formation of a corrie
- BEGINNING: snow begins its process of compression into glacial ice, glacial ice builds up (during last ice age)
- DURING: gravity pulls ice downhill, thawing releases meltwater into any cracks of fractures of exposed rock and freeze thaw takes place, plucking - steepens the backwall, abrasion - deepens the base, rotational sliding occurs ( The process is repeated)
- AFTER: bowl shape is created by rotational movement of ice, corrie loch is trapped behind lip
- during glaciation, continued ice accumulation and rotational movement of the ice will continue to erode the hollow and push ice out of the hollow and over its lip. (this will form the beginning of a valley)
Arête
- a thin ridge of rock formed between 2 adjacent or parallel glacially eroded valleys as the valley walls are worn towards each other
- formed when 2 corrie headwalls erode towards each other
pyramidal peak
an angular and point mountain peak somewhat reminiscent of the shape of a pyramid
- formed when 3 or more corries surround a mountain and erode backwards into it
Glacial troughs ( u-shaped valley)
- after moving out from their corrie birthplace, mountain glaciers occupy and move down pre-existing river valleys and proceed to re-shape them, removing both overlying rock waste and eroding the bedrock both laterally and vertically
Glacial troughs vary in depth and width due to the??
- underlying rock type and its qualities
- size of the glacier
- gradient of the glacier
- climate conditions at the time of glacial action
- type of glacier (cold-based or warm-based)
formation of a u-shaped valley
Before: v-shaped valley in an upland area
During: plucking and abrasion takes place, pushes and removes debris while the glacial ice plucks rock from the base and sides, gravity pulls glacier downwards through valley, vertical and lateral erosion so widens and deepens
- After: identifiable glacial u-shaped valley, much wider and deeper, appear to link/lock together like a zip which lead on the truncated spurs
