Glaciated Landscapes EQ 2 Flashcards
Components of a glacier system
Inputs Dynamic equilibrium Energy Outputs Stores and components Flows and transfers Feedback loops
What are inputs in glaciers
- Precipitation in the form of snowfall, which is compacted over many years to form high density ice.
- Avalanches
- Wind deposition, where strong winds at high altitudes deposit snow
Dynamic equilibrium
- Is the boundary between accumulation zone and ablation zone
- As balance shifts the equilibrium will move up or down
Energy
Glacier mass combined with gravity generate potential energy. As glaciers move down potential energy is converted into kinetic energy. This enables transportation, erosion and deposition
Outputs
Melt water
Ice calving where ice may break off to form icebergs
Evaporation or sublimation
Sublimation is where a solid changes to a gas with no liquid stage
Stores and components
Main stores are snow and ice which change seasonally
Over the last 40 years stores have been decreasing
Flow and transfers
Processes such as meltwater flow and processes of glacial movement such as internal deformation and basal sliding.
Flows and transfers are more active in warmer environments than colder ones
Feed back loops - negative
Wants to maintain dynamic equilibrium to minimise effect of outputs:
- Increased snowfall will increase volume of accumulation, with increased volume of accumulation there will be increases ablation. Glacier will maintain dynamic equilibrium.
Feed back loops - positive
AMPLIFY initial change and may cause a shift in the system to an new state of equilibrium:
- If a glacier has a positive ice mass balance, this increases the albedo effect due to high surface energy. This reduces air temperature causing the glacier to advance.
Factors that cause variation in rate of ablation
Solar radiation
Feedback loops
Warm base or cold base
Type of environment
Factors that effect the accumulation zone
Level of precipitation
Average temperatures
Insulation levels
Wind speeds - strong winds at high altitude deposit more snow.
Poleward aspect - south facing or north facing
Internal deformation
Happens in both warm and cold environments.
2 types of internal deformation:
- Intergranular flow, where ice crystals slip and slide over each other to flow downhill
- Laminal flow, where there is movement of individual layers within the ice
Extensional flow
An increasing gradient causes ice to flow faster and due to internal deformation the ice becomes stretched and crevasses are created.
Compressional flow
Reduction in gradient means ice flows slower. This cause the ice to pile up and thicken. Some crevasses close while some open up.
Between extensional and compressional flow, ice moves in a rotational manner
Transverse crevasses
Cuts across glaciers at right angles
Radial crevasses
Form in a splayed pattern at the snout of the glacier, where ice spreads out in a broad lobe.
Marginal crevasses
Forms near the side where there are different rates of movement due to friction at the sides.
Surge
A great amount of ice movement 100 times faster due to tectonic activity such as volcanic eruptions. This releases a great amount of meltwater which also acts as a lubricant.
Subglacial bed deformation
Sediment can dorm under the weight of the glacier, moving ice on top along with it.
Basal sliding
Happens in only warm base environments.
Involves the movement of large blocks of ice in short jerks. It occurs where meltwater is present to lubricate the base of the glacier.
2 types: enhanced basal creep, and regulation creep.
Regulation creep
Where basal ice melts under localised pressure when it encounters and obstacle. This allows the glacier to flow over it and when pressure is lowered the meltwater refreezes.
Enhanced creep
Where basal ice deforms around irregularities on the bedrock surface.
Feed back cycles of ice movement - negative
A negative feedback - at increasing ice depth the melting point of ice is lowered by pressure. As thickness increases, there is increased pressure and basal slip so ice move faster. In return this reduces ice thickness and reduces pressure melting point and basal slip.
Feed back cycle of ice movement - positive
An increase in basal melt water will increase basal slip, which generates frictional heat and increases basal slip.
Factors that control the rate of ice movement
Gradient- increasing gradient increases flow ice
Meltwater- lubricates base enabling it to slip down hill
Ice temperatures- cold base or warm base
Altitude- affect precipitation and temperature
Permeable or impermeable surfaces- meltwater is retained or not
Friction- ice has to overcome it to move.
Size- an increase in size mean low pressure melting points
Glacial erosion
Abrasion
Plucking
Fracture and traction
Meltwater erosion
Entrainment
The process by which surface sediment is incorporated into a fluid flow as part of the process of erosion
Abrasion
Occurs because of entrainment- large rocks carried below the ice scratch the surface to form striations or scratches
Plucking
When meltwater freezes to a part of the bedrock. Any loose rock fragments are pulled away as glacier the slips forwards.
Fracture and traction
Variation in pressure leads to freezing and thawing of meltwater. This aids plucking.
Meltwater erosion
Glacial meltwater dissolved minerals and carry away salutes
Glacial transportation
Supraglacial- debris transported on the surface of the glacier.
Subglacial - debris transported beneath the glacier
Englacial- debris transported inside the glacier
Glacial deposition
When material is released form the ice at the margin or the base o f the glacier. Deposition may occur on the ground or released in meltwater.
Deposition mechanisms: release of debris by melting, sublimation, release from meltwater and remodelling of deposition.
Glacial landforms occur in different environment
Subglacial - below a glacier
Marginal - at the side of the glacier
Proglacial - in front of the glacier or ice sheet
Different scales for landforms from largest to smallest
Macro scale
Meso scale
Micro scale
Macro scale landforms
Moraines, block fields, ice wedges, pingos, cirques, glacial troughs, till plains, terminal moraines, Sandurs
Meso scale
Kettle holes, ribbon lake, eskers, Roche moutonée, crag and tail, Kame terraces, drumlins
Micro scale
Chatter marks, striations, glacial grooves, erratics
Landform evidence
Upland areas are characterised by erosion although landforms such as carries, glacial troughs and hanging valleys.
Lowland areas tend to have more deposition landforms such as outwash plains and glacial till deposits. Boulder clay tells us that these are areas of glacial deposition that represent former outwash plains. Found in holderness and east anglia. Carries, tarns and glacial troughs in the Lake District provide evidence that glaciers were active in that area.
Variations in glacier mass balance at annual and longer term scales
Levels of precipitations, increased precipitation means accumulation is greater than ablation. This will change the glaciers equilibrium. Precipitation vary annually depending on temperature.
Albedo effect, when there is higher albedo affect temperatures will be lower as radiation is reflected away. This results in more precipitation due to lower temperatures. This is a positive feedback cycle.
Different seasons. In summer ablation is greater than accumulation and glacier shrinks. This is a negative regime. In winter accumulation is greater than ablation and this is a positive regime.
