Glaciation - lithosphere Flashcards
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
Truncated spurs
the bottom part of a slope that juts out onto the main valley, glacier erodes the snouts of the spurs allowed misfit river to run straight down
Ribbon lake
when a valley dammed by the moraine floods, a lake is created, contains twists and turns
Terminal moraine
the material that was pushed in front of the glacier, and left as the glacier melted, formed by material dumped at the sides where 2 glaciers come together
end point of the glacier
rocks, sediments and soil have been plucked and abraded
Hanging valley
a glacial valley whose mouth is found high above the floor of the main u-shaped valley
2 key types of deposits
- till/boulder clay; sediments directly deposited by the ice
- fluvio-glacial deposits; sediments that are deposited by the vast quantities of meltwater
drumlins
- elongated, oval ridges sculpted and streamlined by the action of moving ice
- steep edges and long gentle sloping lee slope
- found in tightly packed clusters - drumlin swarm
Eskers
- long, narrow, steep sided ridges of sand and gravel found within areas of till
- run in the same direction as the glacier
- looks like a railway embankment running lengthways down valleys
kettle holes
- when ice blocks melt, this leaves a depression in the outwash plain
- may also fill with meltwater
- over time may dry out
Outwash plains
gently sloping plains consisting of sands and gravel
- deposited by meltwater streams flowing out from the ice sheet
- begin at the snout of the glacier
Kames
- irregularly shaped mounds composed of gravel and sand that are randomly located on a glacial valley floor
- form from melting ice near glaciers margins and when there is plentiful supple of sediments
- found close to kettle holes and lakes confirming their depression
conflicts of glacial areas - lake district
- litter dumping and camping refuse:
animals could eat litter and die,
eyesore (detract from the pleasant views),
attract vermin such as rats and birds
SOLUTION: no bins policy (force people to take home their rubbish); signs (educating people); employ wardens ( to enforce litter policy); impose fines to fly tipping - Footpath erosion/hillside erosion:
people walking on fragile plants,
destroy the natural habitats ( creates a scar, visual pollution);
SOLUTION: sign posted walks (encourage people to use best routes, cant police this); “fix the fells”, volunteer group (fix paths using local materials, expensive and time consuming); limit people to certain areas
