- Created by: harriet
- Created on: 22-04-11 18:46
The Global Distribution of Cold Environments
Location of Cold Environments:
- Polar - (land & marine) E.g. Antarctica
- Alpine - Areas contain small ice caps, mountain glaciers & tundra environments E.g. Himalayers
- Glacial - covered by ice sheets & glaciers E.g. Greenland
- Periglacial (on the edge of) - cold conditions, create permanently frozen ground (Permafrost), Vegetation is Sparse E.g. Alaska
3 Main influences:
- Proximity to sea - thermal inertia, sea gives out heat even whithout sun
- High latitudes
High Altitudes - every 100m of altitude, temp. decreases by 1 celcius.
Several factos which cause Glaciers in the Accumulation Zone
- higher altitudes there is more ppt, mainly in the form of snow
- snow is highly reflective, absorbs less heat, meaning it melts slower
- Stronger winds at high altitudes cause snow to be blown into hollow and basins so snow accumulates
- temps. are low, sublimination (the change from solid water to vapour) and other losses are low and meltwater is likely to refreeze
In the Ablation Zone, outputs exceed the inputs:
- less snowfall and temps. are higher resulting in outputs: melting (surface, basall and within the glacier), sublimination, evaporation and calving
The dividing line between the 2 zones is called the EQUILIBRIUM line. Gravity moves ice continually towards this line, replacing that lost at the snout by ablation.
Glacier Size and Shape
Nice Glaciers - Small patches of glacier found on upland slopes, mostly north facing
Corrie Glaciers - Small ice masses on mountain slopes, gradually erode arm-chair shaped hollows. Some develop and spill over corrie lip and become a valley glacier
Valley Glaciers - Larger masses of ice from ice-fields or corrie and usually follow pre-glacial river valleys, developing steep sides as they erode their course
Piedmont Glaciers - large lobes of ice formed when glaciers spread out. They may merge on reaching lowland areas and escape the confines of their valleys
Ice Caps - are huge, flatterened, dome shaped masses of ice that develop on high plateaus. They are similar to an ice sheet, but are less than 50,000km in area, if they are over that then they are known as ice sheets. (Antarctic ice sheet has a thickness of over 4000m)
Ice Shelves - extension of ice sheet that reach out over the sea. Shelves can be up to 200m thick
Warm & Cold Glaciers
- Cold Based Glaciers - occur in polar latitudes, where temperature of snowfall is below freezing and the glacier remains below freezing point. Ice remains frozen to bed rock: therefore little movement and limited erosion
- Main type of Movement: Internal Deformation
- Warm Based Glaciers - these are most glaciers outside Antarctica and the northern Greenland ice caps. Water is present throughout the glacier and acts as lubricant. This allows movement (between 20m - 200m per yr) greatly increasing capacity of glacier to erode the bedrock
- Main type of Movement: Basal Sliding/ Surging/ Rotational Movement
Why Glaciers Move
1) Gravity - encourages ice to flow from Zone of Accumulation to Zone of Ablation. Counteracted by friction and small scale electrical charges between crystals which force the ice to bind together
2) Gradient - the steeper the valley, the faster the glacier will flow
3) Mass & Thickness of Ice - Ice doesnt move until 60m thick. At 60m, melting point is lowered, creates melt water and lubricates ice
4) Basil Water Pressure - mass of ice will effect the speed of the subglacial stream. The higher the mass, the increased pressure and therefore increased speed.
5) Temperate/Polar Glaciers - Polar Glaciers are stationary as are frozen to the ground. Stay below PMP. Temperate glaciers have melt water, therfore can move. Stay above PMP.
6) Glacial Budget - higher rates of movement in glaciers that are retreating as there is an increase of melt warer. lower rates of movement in glacier's that are advancing, higher rates of accumulation, colder & less melt water.
Ice is Rigid/Brittle, if theres a sudden pressure it will shatter (Crevasses)
When ice is under a steady pressure, it will deform and refreeze (like plastic)
The top layer in a Glacier is called the RIGID ZONE.
- Crevasses occur here due to sudden pressure.
- This layer moves faster due to less friction
The bottome layer in a Glacier is called the ZONE OF PLASTIC FLOW
- The ice is under steady pressure and so deforms
- layer moves much slower due to friction from bedload and pressure from aboce
From above: Centre of glacier moves faster, least friction here.
From the side: surface of a glacier moves faster than the base. the temp. is low at the base and so freezes to rock aswell as more friction
INTERNAL DEFORMATION: - In cold based glaciers e.g. Meserve Glacier. No meltwater so cannot move by basal sliding (too cold) Moves by Internal Deformation, where the ice deforms and acts plastically. 2 types:
- Intergranular Flow - movement within the glacier resulting from pressure applied by the force of gravity. Ice crystals orientate themselves in the direction of glacier flow, they may slide past eachother, resulting in crevasses within/on surface of the ice
- Laminar Flow - movement within the glacier in layers. Each successive layer is moved by the one layer beneath it. Top layer moves at fastest rate
Extension Flow: As ice flows over steep slope, ice in front pulls away from following ice that has not yet reached the slope. Fractured ice accelerates forward becoming thinner. Forms Crevasses.
When theres a reduction in gradient, ice slows and compresses together. Ice pushes over ice in fron that has a decreased speed, creating Slip Planes.
BASAL SLIDING -
Regelation - glacier moves over obstacle, pressure builds up behind the obstacle causing PMP to decrease and ice to melt. Meltwater flows around obstacle and refreezes once pressure has been released the other side (re'gel' affect).
- the sliding of a glacier over the bedrock by regelation slippage. Friction and pressure between glacier & the bed rock can raise BASIL TEMPERATURES above PMP. A layer of meltwater is created between ice and valley bed, helping to reduce friction and acts as a lubricant helping the sliding process.
- E.G. Franz Joseph moves 300m per yr by Basal Sliding. (accounts for 90% of glacial
Bed Deformation - when the ice is carried saturated bed sediment moving beneath it on a gentle slope, water carried at high pressure (hydrostatic pressure). Compared to ice being carried by Roller Skates
- where gradient in accumulation zone is so steep that is has become unstable, causing a sudden forward movement of the glacier.
- Very rare
Rotational Movement -
- when ice slips around a central pivot point in response to gradient and mass.
- Usually happens in Corries, helps process of Abrasion
How Glaciers Transport Material
1) Supra Glacial (on Top) - Meltwater flows over ice surface and carries Supra Glacial load into Cracks/Crevasses on the surface.
2) Englacial (Within) - Carried within the ice. Supra Glacial material may be covered with snow and become Englacial
3) Subglacial (Under) - Material thats under the Glacier. Could be Moraine, Terminal Moraine etc.
Weathering in Cold Environments:
Glacial Erosion Landforms
- Nivation occurs in small hollow on side of the mountain. Overtime the hollow enlarges & snow compacts to form glacial ice.
- Ice moves through hollow in rotational manner, under weight from the accumulation zone and gravity.
- Rotational movement causes plucking for the backwall, becomes increasingly steep. Debris is gained by plucking/freezet thaw material falling into the burgshrund. Abrasion further deepens the hollow.
- Once hollowed is deepend, the thinner ice at snout loses energy/velocity, unable to erode as effectivily. Rock lip is formed, glacier attempts to travel up lip, friction causes a loss of energy, lacks ability to erode, depostion occurs on corrie lip.
- In summer or post-glaciation when glacier retreats, a deep arm chair shaped corrie is left. May fill with water, called a Tarn
- knife edge ridge, formed when 2 backwalls of a corrie meet eachother
Glacial Erosion Landforms #2
Pyramidal Peaks -
- formed when 3 backwalls of a corrie meet
- very rare, due to orientation, mostly corrie's are north facing
Glacial Trough - E.g. Langdale Valley, Lake District
- formed in previous V shaped valleys in a Glaciation period
- as glacier advances down the valley through gravity, gradient & pressure/mass, spurs are truncated by 'bulldosing effect' leaving a deep, steep sided Glacial Trough
- Post-glaciation period, misfit lakes can be found in Glacial Trough
However, Glacial troughs tend to have a Parabolic shape:
- freeze thaw creates scree, which falls down the sides of glacier to the base, creates a raised side at bottom of U shaped valley,
- usually only one side raised as one is insulated, encourages freeze thaw (more scree)
- Tributary valleys will increase mass of ice at one side of glacier, more mass = more erosion/debris, affecting shape of trough further
Glacial Erosion Landforms #3
Hanging Valley - E.g. Fisher Gill, Lake District
- occurs in tributary valley. When spurs are truncated by glacier in main valley, tributary valley's are left suspended above main valley when glacier retreats
- Waterfalls often occur
Truncated Spurs - E.g. Fisher Gill, Lake District
- originally interlocking spurs, in glaciation period glacier 'bulldoses' though the valley truncating the end of each spur
- easier for ice to erode spurs, rather than travel round them (quicker)
Glacial Erosion Landforms #4
Roche Moutonnee - (roughly between 1-5m in height & 5-20m in length)
- begins when a large resistant rock sticking out of bedrock, when ice hits obsticle PMP decreases due to increased pressure
- meltwater created, encourages Basal sliding over the obstacle - smooths up side of rock by abrasion/plucking
- As pressure is released passed the obstacle, PMP increased again and ice freezes
- Material from plucking is dropped on bottom side of obstacle
Crag and Tail - (same shape as Roche Moutonnee, other way round)
- ice able to erode soft rock, hits resistant rock (crag) unable to erode it
- PMP decreases, meltwater occurs, allows basal sliding over the rock
- flows over crag and begins eroding softer rock behind (tail) diagonally
- erodes at a diagonal angle as gradient, velocity pick up again
Striations - Gauge lines in bed rock left once glacier retreats, caused by rocks frozen into base of glacier. Show direction of ice flow and strength of ice
Glacial Deposition Landforms
1) Till - Material left by glacier
- Lodgement Till - mass of glacier forcing material into the valley bed (sub glacial)
- Ablation Till - material thats dropped when glacier retreats. All sizes, angular rocks due to protection from erosion when frozen in ice. Unstratified, glacier drops till all together
2) Till Sheets - cover the landscape, formed whan glacier was at its largest
3) Ribbon Lake - Meltwater may fill depressions eroded by the ice in valley floor, blocked in by terminal or reccessional moraine. (misfit lake)
Glacial Deposition Landforms
- Lateral Moraine - sides of glacier
- Medial Moraine - middle of glacier, where 2 glaciers meet
- Terminal Moraine - at the end of a glacier
- Ground Moraine - moraine along valley floor
- Push Moraine - shows glacier advance past previous reccesion moraine
- Reccessional Moraine - shows moraine from when glacier retreats
Glacial Deposition Landforms
- rocks that do not fit local geology of the area, carried their by a glacier
- often perched on other rocks called Cap Rocks, protected by Erratic rock
- show us how big the ice mass was & the origin of the ice mass
Drumlins - are elongated hills of glacial deposits. A group of drumlins is called a drumlin swarm or a basket of eggs, eg Vale of Eden.
- Piece of Subglacial Lodgement causes friction beneath glacier, energy loss cause material deposits (unstratified, angular, unsorted) around the lodgement to accumulated, creating a drumlin
- The long axis of the drumlin indicates the direction in which the glacier was moving.
- The gently sloping 'lee end' of the drumlin points in the general direction the glacier traveled.
- steep end of drumlin called 'Stoss end'
4 places Fluvioglacial streams are found in a Glacier?
- Subglacial (under)
- Lateral Streams (Side)
- En-glacial (middle)
- Supra-glacial (top)
Difference between Glacial and Fluvioglacial deposits:
Glacial deposits: unstratified (not deposited in layers), unsorted, angular
- stratified vertically (deposited in layers), due to seasonal variation in flow/type of sediment
- sorted horizontally (largest dropped first)
- rounded (attrition takes place)
Difference between Glacial and Fluvioglacial landforms:
- Glacial landforms: those created/shaped by ice
- Fluvioglacial landforms: those created/shaped by glacial meltwater#
1) Meltwater Channels -
- Ice-marginal stream (edge of glacier)
- Sub-glacial stream (under glacier)
- Pro-glacial stream (in front of glacier)A
All streams are 'discontinous', seasonal: in winter they freeze over. Tend to be short/shallow, travelling fast over frozen bedrock.
2) Sichelwannen - cresent shaped feature on valley sides
- created by Ice-marginal streams
- water pulses every spring eroding cresent shapes into valley sides