Glacial Processes Flashcards
(L1)
What percentage of the Earth do Glaciers occupy today?
10%
What percentage of the Earth did Glaciers occupy 20kya?
30%
What evidence is there in Scotland that glaciers once lay?
Corries formed at the edge of the Cairngorm Plateau, glacially steepend rockwalls and ice scoured plateau till deposits and meltwater channels in the foreground of West Lomond Hill in fife.
What are glaciers?
Topographically unconstrained ice masses
What are the 2 types of morphological glacier?
Continental ice sheets and ice caps
What is the difference?
Continental ice sheets cover much larger area (more than 1,000,000km2) than ice caps (<50,000km2)
Give an example of an ice cap.
Kilimanjaro
Give an example of an ice sheet.
Greenland, Nunataks Antartic Sheet.
What are the three types of topographically-constrained glacier?
Icefields, cirque (corrie), Valley
What is an icefield and give an example?
Similar to an ice cap but constrained by ridges and summits rising above the ice surface eg Columbia icefield, Canada.
What is a cirque glacier and gice an example?
A small glacier that occupies perched hollows on mountains eg Southern Andes
What is a valley glacier and give an example?
Fed by icefields or ice caps or by corries eg, Mer de Glace, French alps
What is the pressure melting point?
The temperature at which ice melts under a given pressure
Give the three thermal classifications of glacier.
Hot, Cold and Polythermal.
What are temperature glaciers?
Warm ice throughout the summer (at pressure melting point)
What are cold glaciers?
Contain Ice throughout winter (below pressure melting point)
What are Polythermal glaciers?
Contain both warm and cold ice.
Which glaciers are frozen to the substrate: cold or warm?
Cold-based glaciers.
which are more erosive: cold or warm?
Warm-based glaciers.
What is the equation for glacier mass balance?
Mass Balance = Net Accumulation - Net Ablation
What are the main sources of accumulation?
Snowfall, snowdrift, avalanches, superimposed ice (refrozen water)
What are the main sources of ablation?
Melt or sublimation of ice at surfaces, adective heat transfer from water, subglacial melt due to geothermal heating, deflation (loss of windblown snow) and calving
What is calving?
Loss of icebergs from glaciers terminating in water
In what circumstances do glaciers advance with a positive mass balance?
When accumulation is greater than ablation
In what circumstances do glaciers retreat with a negative mass balance?
When ablation is greater than accumulation
In what circumstances do we achieve equilibrium line?
When accumulation equals ablation.
What is the cause of glacier movement?
Transfer of ice from the accumulation zone to the ablation zone. Small mass balance = low velocity
At what part of the glacier is movement fastest?
Near the surface and mid line.
What 4 things do glacier velocity depend on?
Basal thermal regime (warm-base faster), mass balance (large faster), bed conditions (deforming faster than bed), bed geometry (ice streams, tidewater-terminating faster)
What are the three mechanisms of glacier movement?
Ice creep, basal sliding and subglacial sediment deformation
Which glaciers undergo ice creep (internal deformation)?
All Glaciers
Which glaciers undergo basal sliding?
Warm-based glaciers
Which glaciers undergo subglacial sediment deformation?
Warm-based glaciers
(L2)
Give examples of micro-scale landforms (<1m)
Striations, crag and tails, friction cracks, p-forms
What are striations?
Scratches produced on bedrock surfaces by abrasion processes.
What is the mode of formation of striations dependent on?
Supply of basal debris, debris concentration, hardness of basal debris/bedrock
What is the mode of formation of micro crag and tails dependent on?
Preservation of small tails of less resistant rock in the lee of more resistant grains or minerals on the rock surface.
What is the mode of formation of friction cracks?
Created when larger clasts beneath the ice are forced into contact with the bed. Clast is rolled or bounced in intermittent contact with the bedrock surface rather than sliding down across it creating crescentic fractures or gouges.
What are p-forms?
Plastically moulded forms used to describe smooth, sinous depressions of large grooves sculpted in bedrock surfaces.
What are micro-scale erosion landforms used for?
To infer basic glaciological information such as broad patterns of glacier flow directions.
Give examples of meso-scale landforms (between 1m and 1km)
Streamlines bedrock features, stoss and lee features, grooves and basins, melt-water channels
What is the mode of formation of streamlined bedrock features?
Product of abrasions processes. More resistant bedrock often left as areas of locally high relief. Eg whalebacks.
What is the significance of streamlined bedrock?
Suggest no basal cavities and therefore high normal pressures at ice.
What is the mode of formation of stoss and lee features?
Produced by a combination of both abrasions and quarrying and therefore have a marked asymmetry form, often occur in clusters and vary in size.
What is the significance of stoss and lee features?
Form where high normal pressure exist om up-ice (stoss) side but pressure is sufficiently low on the down-ice (lee) side allowing a cavity to form and the possibility of quarrying to occur. formation of cavities also allows inferences about ice velocities.
Describe the basic heat pump process.
Latent heat is consumed by melting ice under pressure-cooling the ice. Melt-water may drain away. If the pressure drops melt water will refreeze and latent heat will be released warming the ice. As some of this melt water and therefore a cold patch of ice forms. Beneath this cold patch, ice is frozen to the bedrock and bedrock blocks may therefore be entrained into the glacier as the ice flows back forward.
What is the mode of formation of grooves and basins?
Formed by abrasion or melt water with a similar but larger basin than striations. Enlarged by meltwater. Occur in areas of structural weaknesses.
What is the mode of formation of melt-water channels?
Formation due to melt-water erosion either sub-glacially, along ice margins or in pro-glacial locations.
What is the use of meso-scale erosion landforms?
In general, meso-scale landforms of glacial erosion can be used to infer very basic glaciological information such as broad patterns of glacial flow direction, ice sliding velocities, basal sheer stress.
Give examples of macro-scale landforms?
Areal scouring, glacial troughs, cirques, giant stoss and lee features, tunnel vallys.
What is the most commonly encountered macro-scale landscape feature produced by glacial erosion?
Areal Scouring
What is areal scouring?
A large area of scoured whalebacks, roches moutonnees and rock basins.
What is areal scouring known as in the UK?
Knock and Lochan topography
What are glacial troughs?
Deep linear features carved out into bedrock exploiting lines of weakness within bedrock associated with valley or outlet glaciers (confined ice flow) but may be cut beneath an ice cap.
How are cirques formed?
Cirques are eroded by rotational ice flow in discrete patches of glacier ice, although they can, in conditions favorable to glacier expansion drain into valley glaciers.
What are cirques used for?
Looking at reconstruction dimensions of former cirque glaciers. This allows inferences to be made about snowline altitudes and equilibrium line altitude.
What can thus be calculated on regional scale?
The paleo-temperature and paleo-precipitation estimates.
when is an arete formed?
when two glaciers carve back into the headwall of the mountain wall.
When more that two glaciers are eroding the mountain, what do they form?
A horn
(L3)
What is a Morraine?
A mound, ridge or other distinct accumulation of general unsorted, unstratified glacial debris, deposited by direct action of glacier ice.
How are Morraines formed?
Through the processes of plucking, rock falling from valley sides and bulldozing like action, glacier collects unconsolidated debris and includes it in the mass of ice.
What is a push morraine?
A ridge, composed of bedrock, till or other material that was either pushed by glacier ice or dragged along the base. After ice retreat, the material is left stacked in a series of ridges in the landscape.
What is ablation moraine?
An irregular-shaped layer or pile of glacier sediment formed by the stagnant ice, Ultimately, ablation moraine is deposited on the former bed of the glacier.
What is a rogen moraine?
A morraine set perpendicular to the direction of ice flow, formed of large scale transverse ridges giving the overall appearance of an animal’s ribs. The ridges, consisting of till for the most part, are generally steep-sided.
What is a De Geer Moraine?
A morraine set perpendicular to the direction of iceflow, forming a low, relatively narrow ridge of water-sorted till; De Geer moraines are deposited in shallow bodies of water at a glacier snout.
Where can terminal, lateral, medial and ground morraines be found?
At the furthest point reached by a glacier, deposited along the side of the glacier, found at the junction between 2 glaciers, piles of various shapes and sizes and different rock types.
What is a drumlin?
An elongated hill of glacial deposit. The long axis of which indicates the direction in which the glacier was moving.
What is an erratic?
Very angular and unsorted glacial deposits found on their own.
What is a glacial flute?
A landform created by the movement of a glacier around a boulder which is on long parallel ridges.
What is an esker and how was it formed?
A long winding ridge of stratified sand and gravel that formed within ice-walled tunnels by streams which flowed within and under glaciers
What are kames?
Steep conical hills composed of glaciofluvial sediments. developed when glacial crevasses and depressions in stagnate glacial ice are filled with sand and gravel deposits form sediment loaded meltwater,
What are kettle lakes?
A shallow, sediment filled body of water formed by retreating glaciers or draining floodwaters.
Can stoss and lee features be macro-scale too?
Yes
What are the uses of maccro-scale erosion landforms?
As at other scales, each macro-scale landform has particular glaciological conditions for its formation. Same as meso mostly.
