Glaciers - Enquiry Question 2 and 3 Flashcards
Positive glacier regime
When the glacier is increasing in mass (when accumulation exceeds ablation), e.g. during the winter months
Negative glacier regime
When the glacier is decreasing in mass (ablation exceeds accumulation), e.g. in the summer months
What percent (estimated) of the world’s ice masses currently reducing in size?
75%
Negative feedback cycles
- Acts to minimise the effect of new inputs in order to regain stability and equilibrium
- Increased inputs = increased outputs
Positive feedback cycles
- Amplifies the effects of an input which would cause a shift in the system
- Growing glacier - increased albedo effect = more ice = glacier advancing
- Retreating glacier - decreased albedo effect = more melting/less reflection = glacier retreating
Describe the difference between positive and negative feedback (4)
Negative feedback is when the cycle acts to minimise any changes and regains an equilibrium. For example, the implications of a glacier receiving an increase in snowfall provides the foundation for it to advance. Subsequently, this would cause the glacier to advance further down the valley with the consequence of more ablation and displacement of ice, balancing out the system.
Conversely, positive feedback is when the cycle amplifies the effects of a change resulting in an imbalance. For example when a glacier has a negative mass balance, there is persistent ablation. The implications of this is that the albedo effect will decline, fundamentally causing temperatures to increase thereby contributing to further ablation reinforcing the change.
Greenland Ice Sheet
- One of the world’s 2 remaining ice sheets
- Contains more than 2.5 million km³ of ice
- Has an area of 1.7 million km²
- 3km thick at the centre
Inputs and mass balance of the Greenland ice sheet
- +520 accumulation of snowfall in central areas
- -290 ablation of melting edges
- -200 ablation by calving icebergs
- -60 ablation by summation
- Mass Balance = -30 (the Greenland ice sheet is retreating)
Positive feedback loops occurring at the Greenland ice sheet
- Snow/ice melt (greenhouse effect) → melting reveals bare ground → Albedo effect reduced, acceleration of land warming up → less reflection of solar radiation → increased global warming
- Snow/ice melt (greenhouse effect) → melting reveals bare ground → methane released into the atmosphere → increased global warming
Positive feedback loops occurring at the Greenland ice sheet
- Snow/ice melt (greenhouse effect) → melting reveals bare ground → Albedo effect reduced, acceleration of land warming up → less reflection of solar radiation → increased global warming
- Snow/ice melt (greenhouse effect) → melting reveals bare ground → methane released into the atmosphere → increased global warming
Pressure Melting Point (PMP)
- Temperature at which the ice is on the verge of melting
- Glacier surface = 0°C
- Can be lower within a glacier due to increased pressure, so ice can melt below 0°C
How does altitude affect glacier movement?
Affects precipitation and temperature. Greater precipitation and lower temperatures increase the supply of snow and ice, and so its mass balance
How do gravity and gradient slope affect glacier movement?
Gravity causes ice to move; the steeper the gradient, the faster it flows
How does ice mass/thickness affect glacier movement?
The heavier/greater the mass, the greater the pressure in the ice, which causes faster movement
How does rock type affect glacier movement?
If rock is permeable, then meltwater may percolate through, slowing the movement of the glacier. If rocks are impermeable, there will be more meltwater, causing the glacier to move quicker
How does ice temperature affect glacier movement?
Colder ice moves slowly as it does not deform as easily, and it stays stuck to the bedrock
How does meltwater affect glacier movement?
The more meltwater there is, the faster the movement as basal slippage increases
Inter-granular movement
Individual ice crystals slip and slide over each other
Intra-granular movement
Ice crystals deform due to stress within the ice and eventually moves downhill under the influence of gravity
Basal slip
This occurs when the base of the glacier is at the pressure melting point, which means they meltwater is present and acts as a lubricant, enabling the glacier to slide more rapidly over the bedrock. Basal slip can be further subdivided into several processes: creep and regelation, extending and compressing flow, and surges
Creep and regelation
Basal slip is enhanced by obstacle on the valley floor. A large bedrock obstacle (>1m wide) causes an increase in pressure, which makes the ice plastically deform around the feature (creep). Smaller obstacles (<1m wide) will cause pressure-melting, increasing ice movement by basal slip. The ice refreezes on the downglacier (lee) side of the obstacle. The process of melting under pressure and refreezing is known as regelation
Extending and compressing flow
Over steep slopes, the rate of basal slip will increase and the ice will accelerate and thin. This is known as extending flow. Over shallower slopes, basal slop shows and the ice decelerates and thickens. This is known as compressing flow
Surges
In these short-lived events a glacier can advance substantially, moving up to 100 times faster than normal. They have various causes (e.g. earthquakes) but the most common is enhanced basal sliding triggered by the build-up of meltwater at the ice-rock interface
Internal deformation
This occurs when the weight of glacier ice and gravity causes the ice crystals to deform, so that the glacier moves downslope very slowly
Explain 2 processes that shape a glacier landscape (8)
One process that shapes a glacial landscape is erosion. Plucking, or quarrying, is one erosional processes that contributes to shaping the landscape. Plucking occurs predominantly from weathering, when sediment within the glacier allows basal meltwater to enter the joints and cracks, also going around the rock, which then freezes. As the glacier ice moves, it pulls the rock with huge pressure, the consequences of which results in the rock being plucked from tis position. This shapes a glacial landscape because as rocks are plucked from their location, parts of the landscape are removed, which means that the environment becomes very jagged.
A second erosional process that shapes a glacial landscape is abrasion. Abrasion occurs when angular frost-shattered material is carried below the ice which means that it persistently scours the rock beneath it. This shapes a glacial landscape because as the frost-shattered material moves over the rock, it scratches it, creating striations or, if the material is rock flour, it polishes the underlying rocks, which means they either scratches are produced as evidence on the surface of rocks or rocks are very smooth.
Movement of cold-based glaciers?
These move mainly by internal deformation, by 1-2cm per day (e.g. Greenland Ice Sheet)
Movement of warm-based glaciers
They can move up to 3m per day, by _______ (e.g. the Alps)
Supraglacial
Weathered material carried on top of a glacier
Englacial
Weathered material carried on top of a glacier, then buried by fresh snow
Subglacial
Material carried below the ice
Till
Material deposited underneath ice, single pebble or small rock
Eratics
These are till that have been transported to another with different geology, large rock or boulders
Moraine
Generic term for landforms associated with the deposition of till from within, on top of, and below a glacier, e.g. a pile of till
Macro-scale glacier
Large scape landforms, around 1km or greater in size and form the major elements in a glaciated highland landscape, e.g. u-shaped valley
Meso-scale glacier
Medium-scale landforms largely found within macro features, e.g. found on a valley floor, e.g. drumlins
Micro-scale glaciers
Small-scale landforms less than 1m long, e.g. striations
Eratics example
Huge eratics, weighing up to 16,000 tonnes, were carried over 300km from Canadian Rockies to the plans of Alberta by the Cordilleran ice sheet
Medial moraines
This is formed when lateral moraines from two merging glaciers join up - leaving a line of debris in the centre of the combine glacier’s flow. As the combined glaciers melt, the medial moraine is deposited to form a low ridge
Lateral moraines
A high and almost symmetrical ridge, formed along the outer edge of a glacier. It can ne several metres high. Formed from freeze-thaw on the valley sides that causes the material to fall onto the edge of the glacier below
Recessional moraines
Retreating glaciers may experience periods of stability, when a secondary ridge of sediment forms at the snout. This has the same characteristics as terminal moraine, but doesn’t mark the furthest extent of the ice
Terminal moraine
A ridge of sediment piled up at the furthest extent of an advancing glacier. It commonly appears as a line of hills (rather than a solid ridge) due to the erosive action of meltwater streams from the retreating glacier
Drumlins
- Oval or ‘egg-shaped’ hill made up of glacial till
- Aligned in the direction of ice flow
- 30-50m higher, 500-1000m long
- Occur in clusters or ‘swarms’ on flat valley floors or lowland plans and forming ‘basket of eggs’ topography
Ice Marginal
Environments at the edge of a glacial ice where a combination of glacial and fluvioglacial processes occur
Till Plains
Formed when a large section o ice detaches from the main body of the glacier and melts. The suspended debris will be deposited and form a large plain of unsorted till
Lodgement till
- Lodgement is a process that occurs beneath the ice mass when subglacial debris that was being transported becomes ‘lodged’ or stuck on the glacier bed
- Lodgement occurs when the friction between the subglacial debris and the bed becomes grater than the drag of the ice moving over it. It is commonly associated with glaciers carrying huge loads of debris and where the glacier is very slow moving, if not static
Ablation till
Ablation is material that has been dumped as the glacier melts and thaws. It can include material that has travelled within the glacier at any point i.e. supraglacial, englacial; and subglacial
Upland
Those at higher altitude in hills and mountains
Lowland
Those at lower altitudes on valley floors and coastal plains
Active
Currently experiencing glaciation, active glacial processes and landform development
Relict
These are landscapes that aren’t characterised by glaciers (ice) but feature fossilised glacial landforms, due to past glaciation
Fluvio-glacial
- Water processes working with ice
- Meltwater travels in the same places material travels in a glacier system (supra/en/sub-glacial)
How do glacial outbursts occur? What can they cause?
Occasionally, a huge amount of meltwater becomes trapped, either beneath the ice or as surface lakes. When these eventually burst (glacial outburst), the surging meltwater has the power to carve deep channels or gorges
Kame
- An undulating mound of fluvio-glacial sand and gravel deposited in the valley floor near the glacier snout
- As meltwater streams emerge onto the outwash plain or proglacial lake at the glacier snout, their velocity suddenly falls and sediment is deposited
Kame Terrace
- A flat, linear deposit of fluvio-glacial sand and gravel deposited along the valley sides
- During the summer the valley sides radiate heat, melting the edge of the glacier and forming meltwater streams, which deposit sediment. When the glacier retreats, the sediment will fall to the valley floor, forming a kame terrace
Meltwater channel
- A narrow channel cut into bedrock or deposits either underneath or along the front of an ice margin
- Meltwater can erode deep channels, even gorges, as a result of hydrostatic pressure within the glacier and their high sediment load. They have some unique characteristics: under hydrostatic pressure beneath the glacier; they are able to flow uphill and they are often larger than post-glacial streams; and braiding of proglacial meltwater channels is common, due to seasonal variations in discharge
Proglacial lake
- A lake formed in front of the glacier snout
- A proglacial lake is often formed by the damming action of a terminal or recessional moraine during the retreat of a melting glacier, or because hills block the escape of meltwater. It can also be formed by meltwater trapped against the ice sheet as a result of isostatic depression of the crust around the ice
Sandur/outwash plain
- A flat expanse of fluvio-glacial debris in front of the glacier snout
- As meltwater streams emerge from the glacier and enter lowland areas, they gradually lose their energy and deposit their debris load. The coarse gravels are deposited first, nearest the glacier, then the sands, an finally clay, farthest from the glacier
Esker
- A long, narrow, sinuous (winding or meandering) ridge of fluvio-glacial sand and gravel
- Subglacial streams cab=n carry large amounts of rock debris due to their high hydrostatic pressure inside tunnels. The streams often meander beneath the glacier. When the glacier retreats, the debris load is deposited at a consistent rate and forms a ridge
Kettle hole
- A circular depression, often forming a lake in an outwash plain
- As the glacier retreats, detached blocks of ice remain on the outwash plain. Meltwater streams flow over ice, covering them in deposits of fluvio-glacial debris. Eventually the ice melts and the debris subsides to form a depression, which often fills with meltwater to form a kettle-hole lake
Fluvio-glacial deposits, as opposed to till
- Smaller due to energy of meltwater (attrition in rivers)
- Smoother and rounder
- Sorted horizontally
- Stratified (layers) vertically with distinctive layers which reflect either seasonal or annual sediment accumulation
Clast shape (characteristics of till and fluvio-glacial deposits)
- Clasts (rock fragments) may be angular or show evidence of rounding
- Till: clasts are aligned in the direction of ice movement but often horizontal and maintaining their angular shape
- Fluvio-glacial debris: the process of attrition in meltwater makes clasts more rounded
Imbrication (characteristics of till and fluvio-glacial deposits)
- The clasts have a preferred orientation and dip caused by a strong current
- Till: clasts are aligned in the direction of ice movement but often horizontal rather then dipping, unless part of a push moraine
- Fluvio-glacial debris: clasts are aligned in the direction of low and often dip upstream
Stratification and grading (characteristics of till and fluvio-glacial deposits)
- The deposit is layered, with coarse sediments at the base, grading upwards into progressively finer ones
- Till: unstratified - clasts are umped chaotically by the glacier
- Fluvio-glacial debris: rock fragments are stratified and graded by seasonal variation in meltwater discharge. A layer of fine grains in deposited in spring and summer when discharge is high; a layer of coarse grains is deposited when discharge falls in autumn and winter
Sorting (characteristics of till and fluvio-glacial deposits)
- Sorted sediment has a common grain size
- Till: unsorted - ice has enough energy to transport a wide range of grain sizes, from fine rock flour to large bounders
- Fluvio-glacial debris: the seasonal variation in stream discharge sorts the grains into layers of consistent size
Environmental factors (value of relict and active glaciated landscapes)
- Water cycling
- Climate control
- Carbon cycling
- Weather system control
- Fragile ecosystem
- Carbon sequestration
- Genetic diversity
Cultural factors (value of relict and active glaciated landscapes)
- Spiritual/religious inspiration
- Leisure and recreation opportunities (e.g. skiing)
- Native people with distinctive cultures
- Scientific research (e.g. ice core analysis)
Arctic casestudy
Greenland casestudy
Economic value of active/periglacial environments
Little economic value, as they’re considered ‘true wilderness’. This is because they’re remote and have harsh physical environments, and they carry little to no populations
Economic value of relict environments
High economic value, as they could be densely populated, and provide opportunities for economic development and employment (e.g. the Lake District)
Farming (economic activity)
- In developing countries, mountainous regions suffer from limitations in transport links, access to essential supplies and markets and employment opportunities in countries such as Nepal, Bolivia (Altiplano) and Ethiopia (Bale Mountains), the highlands are largely inhibited by indigenous communities who gain their living from subsistence farming (growing crops to feed themselves)
- In Bolivia 70% of people live in the High Andes, growing crops such as potatoes, quinoa and beans to feed themselves, as well as rearing llamas and alpacas, yet they only earn 30% of the country’s GDP. Almost all of the 60% of Bolivia’s population living below the property line are indigenous Indians living in the Altiplano of the High Andes
- In Alpine areas in developed countries, the agriculture in upland regions is primarily pastoral (livestock) because of the above-average precipitation, rugged terrain with steep slopes and stony, shallow soils, which together make growing crops very difficult. In the truly Alpine areas a traditional farming system is used to take advantage of the seasonal climate cycle - in summer animals are grazed at high altitudes on Alpine Meadows, which becomes free from snow and provide high quality grass - at the same time, the grass in the valley bottom can be made into hay for winter feed which is used when the animals are brought down in the winter
Tourism (economic activity)
- The tourist industry has seen a large increase in recent decades, which has brought many economic benefits to mountainous regions, with visitors attracted to the spectacular scenery of both present-day and relict glaciated landscapes
- A huge range of year-round, outdoor activities are possible in Alpine landscapes such as hill walking, climbing, mountaineering and skiing
- Thanks to long-haul travel and modern communications, mass tourism is not only affecting traditional area such as Swiss Alps but also affecting more remote polar regions in the Arctic (Alaska, Greenland and Iceland) and Antarctic (South Georgia and the Antarctica Peninsula)
- Other Developing areas are: Everest base camp and ascent, Nepal; Franz Josef and Fox Glaciers, New Zealand for guided walks, heli-rides and heli-skiing on the glaciers; and Mer de Glace, Chamonix French Alps to get the cable car to Aiguille du Midi for glacier viewing and hiking as well as visiting the ice cave beneath the glacier
Forestry (economic activity)
- Upland areas are being used increasingly for forestry due to the difficulty to use the land for hill farming
- In the UK this is carried out by the Forestry Commission and private investors, with the main type of tree being non-native, quick growing conifers such as Sitka spruce, grown for softwood timber, wood pulp and even paper
- Conifers tolerate harsh climates and acidic soils that would not be suitable for other land uses
Mining and Quarrying (economic activity)
- Glacial erosion plays an important role in removing regolith (loose overlying soil) and vegetation to expose economically valuable rocks
- In many active or relict areas there are mines and quarries of mineral deposits and ores, as well as rocks such as slates as many of the glaciated mountains are made from igneous and metamorphic rocks
- In lowland area, outwash deposits from the Pleistocene Ice Sheets provide a very important source of sand and gravel for the building industry, pre-sorted by meltwater into sands and gravels to be sold as aggregates, making them very useful for making concretes
Hydroelectricity (economic activity)
- Hydroelectric power (HEP) is a major use of water derived from glaciers
- Both Norway and New Zealand derive over 90% of their electricity from this source
- In most cases either natural ribbon lake or a dam and reservoir in a glaciated valley provide HEP
- Switzerland have over 500 HEP stations producing 70% of its electricity
- Clearly HEP is a renewable ‘green’ source, although there are issues with both the reliability of water supply and environmental concerns over damming rivers
- In mountain settlements in developing nations, such as Nepal and Bolivia, micro-hydros can revolutionise the quality of life in many villages
What percentage of the Earth’s carbon is stored in permafrost?
14%
Scientists in Alaska’s Arctic Long Term Ecological Research Site set up artificial warming plots over 20 years. What did they find?
Increased growth of shrubs at the expense of mosses, sedges and grasses - this results in a negative feedback loop as the carbon hasn’t been released into the atmosphere and contributed to higher atmospheric greenhouse gas levels (positive feedback)
Threats to glaciated landscapes - Avalanches
An avalanche exists where sheer stress exceeds sheer strength of a mass of snow located on a slope
- While avalanches tend to follow well-known tracks ad can often be predicted they are nevertheless a significant hazard, usually killing around 200 people per year with most of these deaths in the Alps and the Rockies
Threats to glaciated landscapes - glacial outburst floods
- A glacial outburst flood is a powerful flood caused by the sudden discharge of a subglacial or ice moraine dammed lake
- There is potential for an outburst flood whenever meltwater collects behind an ice or moraine obstruction
- These very large floods are a huge threat to people and property in inhabited mountain valleys
Threats to glaciated landscapes - leisure and tourism
- Resorts in glaciated regions, particularly ski resorts, attract large amounts of people each year (e.g. Zermatt in Switzerland attracts 2 million visitors per year)
- At the height of the ski season the resident population in Zermatt can be as high as 35,000 - this creates a huge demand for energy and water, which threatens environmental degradation due to urbanisation, increased noise and vehicle emissions and the expansion of ski areas
Threats to glaciated landscapes - reservoir construction
- As glaciers store 69% of the world’s freshwater, many countries are tapping into the source, especially due to fears of summer water shortages due to glacial retreat
- Within the Chinese side of the Tibetan Plateau, there are nearly 37,000 glaciers, containing the largest volume of ice outside the polar regions and also giving birth to many rivers across Asia including the Ganges
- Almost 2 billion people in more than a dozen countries depend on these ice fed rivers
- China aims to build 59 reservoirs to capture and save glacial run-off for the future
- Reservoir construction would require intense, heavy machinery and the clearing of land as well as irreversible damage to wildlife
Threats to glaciated landscapes - urbanisation
- Traditionally, the development of settlements in relict glaciated areas has been for agricultural purposes, however in polar environments this is not the reasons
- Settlements in polar regions tend to be surrounded by nothing and tend to be built for resource exploitation purposes including whaling, mining and fishing
- Inevitably, there are issues with pollution and toxic waste as ell as conflicts occurring between these outsiders and native people
- Regular contact from outsiders has reduced chances of survival of traditional culture groups e.g. the Inuit in Greenland
Arctic tundra ecosystem
- Tundra plants have to adapt low temperatures, drying winds and snow blasts in winter blizzards
- The Arctic is a harsh environment, with long, dark winters and short summers. The growing season only lasts for 3 months - when average temperatures rise to 12°C
- Vegetation occurs in periglacial areas that aren’t covered in ice, both in high latitudes (Arctic) and high altitude (Alpine), covering around 8 million km² of the Earth’s surface
Lower Arctic Latitudes (around 70-75°N)
- Continuous cover of ground vegetation including sedges and mosses in the wetter holloes and scattered dwarf trees (elder and birches) on the lower ridges
- Elsewhere heaths, grasses and rapidly flowering plants flourish
High Arctic Latitudes (around 75-80°N) and Higher Altitudes
- Polar desert conditions prevail
- However, a small range of plants survive in favourable sheltered locations such as the purple saxifrage (has cushion-shaped moss, the flowers have increased surface area exposed to the sun by facing it) and the arctic poppy
Summer in an Arctic Tundra
- The surface layer of permafrost melts to form bogs and shallow lakes
These attract insects, which in turn attract migrating birds - The tundra also supports a variety of larger animals such as the Arctic Fox, grey wolves, snow geese and musk oxen (most of these migrate)
Winter in an Arctic Tundra
- Temperatures fall well below freezing
- Plants - which many animals rely on for food - must survive under the snow to re-emerge and flower quickly once temperatures rise again in the spring (animals may hibernate until warmer temperatures)
Endemic
Of a plant or animal) native and restricted to a certain place.
“a marsupial endemic to north-eastern Australia”
Overall, what percentage of the world’s water do glaciers hold?
2%
How much water on average is transported from the Alps (‘water towers of Europe) every year to nearby regions?
216km³
Sagarmatha National Park, Nepal - casestudy
Greenland Climate Change - casestudy
Lake District, England, footpath erosion - casestudy
Zermatt, Switzerland - casestudy
Iceland, outburst floods - casestudy
Arctic and Antarctic Tourism - casestudy
Threats of global warming - causes
- Agriculture
- Deforestation
- Burning fossil fuels
- Industry
- Mining
- Population changes and urbanisation
- Natural causes
Threats of global warming - impacts
- Decreased albedo effect
- Increased insolation
- Ice melt
- Rising sea levels (by 2100, levels expected to have risen by 33cm) - leads to coastal flooding
- Seasonal changes
- Extreme weather (increased power of tropical storms)
- Drought
- Food and water shortages
- Migration of wildlife
What percent of mass have all glaciers on the East slope of the Rockies lost since 1850?
25-75%
