Flashcards
Warm and cold-based glaciers
Cards in this deck (32)
- 1FORMATION OF GLACIER ICEGlaciers form when temperatures low enough for snow that falls in one year to remain frozen throughout the year > following year fresh snow falls on previous year’s snow
Fresh snow - flakes with open, feathery structure + low density (0.05g/cm3)
Each new fall of snow compresses + compacts layer beneath causing air to be expelled converting low density snow into higher density ice
Firn = snow that survives 1 summer, density 0.4g/cm3 - 2DiagenesisProcess by which snow becomes ice due to compression
Glacier ice density 0.83-0.91g/cm3
May take 30-40 and 1000 years
Depth 100m, bluish colour die to lack of air - 3VALLEY GLACIERS AND ICE SHEETSGlaciers large, slow-moving masses of ice
Ice sheets largest accumulation of ice, greater than 50,000km2
Only 2: Antarctica and Greenland
Antarctic ice sheet covers 13.6millionkm2
Valley glaciers confined by valley sides, follow course of existing river valleys
May be outlet g”aciers form ice sheets or fed by snow and ice from Corrie glaciers
10-30km in length - 4WARM-BASEDHigh altitude locations
Steep relief
Basal temperature at or above pressure melting point
Rapid rates of movement (20-200m a year) - 5Active with large volumes of ice transported across equilibrium lineSignificant seasonal advance and retreat
Locations e.g. alps and rookies high rates of accumulation in winter + high rates of ablation in summer
Rapid ice movements >> significant erosion + erosional landforms
Ablation also produces lots of meltwater > glacio-fluvial landforms - 6COLD-BASEDHigh latitudes
Low relief
Basal temperatures below pump so frozen to bedrock
Very slow rates of movement - 7Minimal seasonal differencesIn Antarctica and Greenland summer temperatures below freezing and precipitation low > limited accumulation and ablation
Not very dynamic - limited movement and landscape impact as little erosion, deposition and transportation can take place - 8Differences:Most important difference = basal temperature (and relationship with pmp) > determines mechanism of movement
- 9Pressure melting pointTemperature at which ice melts under pressure
0*C at surface
Lowered within ice mass due to increasing pressure - 10Temperate glaciersAt pmp at base and sometimes within
Movement facilitated by production of meltwater - 11Polar glaciersTemperatures below pmp and movement limited
- 12Glacier movementFundamentally due to forces of gravity
Ice moves downslope (from accumulation zone, across equilibrium line, to ablation zone) - 13Factors influencing movementGravity - causes glaciers to move due to weight
Gradient - steeper gradient, faster glacier will move downslope due to greater effect of gravity
Thickness of ice - thicker ice, greater pressure so ice will melt at lower temperature > more meltwater increases movement of glacier
Internal temperatures of ice - affects melting of ice (meltwater lubricates glacier) + can allow movement of one area relative to another
Glacial budget - positive glacial budget causses glacier to advance - 14Upper zoneIce brittle + breaks > crevasses
- 15Lower zoneIce deforms under pressure (behaves like plastic)
- 16Sides + base of glacier move more slowly than top and middle(James Forbes Alps 1842)
Ice frozen onto rocks of valley floor + sides
Obstructions creating frictional resistance + slowed movement
Accumulative effect of LAMINAR FLOW > lower layer of ice moves itself + carries layers above with it - 17BASAL SLIDINGWarm-based glaciers
If basal temperature at/ above pmp a thin film of meltwater exists between the ice and valley floor > friction reduced - 18Combination of different mechanisms:Slippage
Creep/ regelation
Bed deformation - 19SlippageIce slides over valley floor as meltwater has reduced friction between base of glacier (inc debris embedded in it) and valley floor
Friction between moving ice/ debris and valley floor can also lead to creation of meltwater - 20Creep/ regelationIce deforms under pressure due to obstructions on valley floor > enables it to spread around and over the obstruction + refreezing again when pressure reduced
- 21Bed deformationIce carried by saturated bed sediments moving beneath it on gentle gradients
Water under high pressure - 22Franz Josef glacier New ZealandWarm-based
Moves 300m a year - 23Salmon glacier CanadaBasal sliding 45% movement
Can be up to 90% extreme cases - 24INTERNAL DEFORMATIONCold-based glaciers unable to move by basal sliding as basal temper below pmp
(But ice at 0*C deforms 100 times quicker than at -20*C) - 252 elements:Inetrgranular flow
Laminar flow - 26Intergranular flowIndividual ice crystals re-orientate and move in relation to each other
- 27Laminar flowMovement of individual layers of within glacier - often layers of annual accumulation
- 28Occur when glacier is on a slopeNot on level surfaces where ice remains intact
- 29Meserve glacier AntarcticaOnly moves 3-4m a year at its equilibrium line (all by internal deformation)
- 30Extending flowWhen ice moves over a STEEP slope it’s unable to deform quick enough so fractures > forms crevasses > leading ice pulls away from the ice behind which has yet to reach the steeper slope >> thins
- 31Compressing flowGRADIENT REDUCED > ice thickens as following ice pushes over slow-moving leading ice
- 32SurgesOccasionally up to 100m a day
Steep gradients in temperate glaciers after large input of snow and ice
Some triggered by tectonic activity
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- - Geography (Glaciers) Flashcards on Warm and cold-based glaciers, created by Emily H on 18/11/2018.
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