Physical - Glaciated Landscapes Flashcards
Abrasion
Abrasion involves the wearing down of rock surfaces by the grinding effect of rock fragments frozen into the base of glaciers. A good analogy of this process is sand papering and through its action it produces smoothed bedrock surfaces that often exhibit parallel sets of scratches (1-10mm diameter), called striations. Abrasion forms fine silt-sized particles (0 .1mm) known as rock flour, which causes the milky appearance of melt-water streams
Factors that influence abrasion
- Ice velocity: abrasion is greater beneath fast flowing glaciers since more debris passes a given point per unit of time
- Basal rock debris: abrasion can only occur if rock debris is present at the ice/rock interface. Clean ice cannot scour its rock bed and the rate of abrasion increases with basal debris concentration, furthermore, the abrading rock fragments must be harder than the bedrock surface beneath
- Removal of rock flour: in order to sustain abrasion rock flour needs to be flushed away from the glacial sole by a constant supply of meltwater, otherwise the ice/rock interface would clog-up with fine debris reducing the direct contact between abrading clasts and the underlying rock surface
Plucking
Plucking is the removal of well jointed or loosened blocks of bedrock by an overriding glacier. Blocks freeze onto the glacier sole and are then pulled clear of the rockmass as the ice moves forward. Once plucked the blocks become the grinding tools that cause abrasion. Plucking is particularly effective where a glacier flows over rock that has are ready been weakened by frost weathering
Crushing
Crushing occurs when the pressure exerted by basal rock fragments crushes the bedrock surface beneath to leave cresentic fractures called chattermarks
Meltwater erosion
The streams of meltwater that flow along the base of a glacier erode rock in the same way as surface streams, through the combined action of abrasion, hydraulic action, attrition, and solution. However,
there is one important difference, water at the base of a glacier is squeezed by the enormous weight of ice above (hydrostatic pressure). This causes meltwater streams to flow much faster, hence, the erosive
potential of meltwater streams is significantly greater than surface rivers
Freeze-thaw
Occurs when water continually seeps into cracks, freezes and expands, eventually breaking the rock apart
By how much does water expand when it freezes?
9-10%
Mass movement
The bulk movements of soil and rock debris down slopes in response to the pull of gravity
Slumping
- A form of mass movement that occurs when a coherent mass of loosely consolidated materials or a rock layer moves a short distance down a slope
- Occurs in sections
Sliding
This happens when a section of soil or rock suddenly gives way and moves down a slope
Rockfall
Bits of rock fall off the cliff face, usually due to freeze-thaw weathering`
Cirque
- An armchair-shaped hollow on a hillside above a glacial valley
- Pre-glacial hollow is enlarged by plucking and abrasion as ice moves in a rotational manner under gravity
Arête
- A narrow, knife-edge ridge between two cirques
- As two cirques erode backwards, the ridge between them becomes increasingly narrowed
Pyramidal peak
- A sharp, pointed hilltop
- As 3 or more cirques erode backwards/enlarge, the hilltop between them becomes increasingly sharp and pointed
- e.g. the Matterhorn, the Alps
U-shaped valley
- A steep-sided, flat-floored straight valley
- A pre-glacial river valley is widened and deepened by erosion from an advancing glacier
Truncated spur
- A steep and possibly rocky section of the side of a trough
- The pre-glacial interlocking spurs of the river valley are eroded by the much more powerful glacier
Hanging valley
- A small tributary valley high above the floor of the u-shaped valley, often with a waterfall
- Tributary glaciers with small amounts of ice did not erode their valley floor as deeply as the main glacier and so are left at a higher altitude
Roche Moutonnée
- Asymmetrical, base rock outcrop with a gently sloping side facing up-valley (smooth stoss, jagged lee)
- As ice crosses a resistant rock outcrop, the increased pressure causes melting and basal sliding and the up-valley side is smoothed by abrasion
- On the leeward side pressure is reduced, refreezing occurs and plucking takes place, causing a steep, jagged slope
Knock and lochan
A glaciated landscape of low relief which is made up of ice-moulded hillocks and intervening lochans (small lakes) eroded along zones of rock weakness
Crag and tail
A landform consisting of a rock hill and tapering ridge, which is produced by selective erosion and deposition beneath an ice sheet
- The crag is steep-sided and has cracks in it from plucking
- The tail is has a gentler gradient, due to it being made up of less-resistant rock; moraines are often deposited here
Lateral moraine
- A ridge of moraine along the edge of the valley floor
- Exposed rock on the valley side is weathered and fragments fall down on the the edge of a glacier. This is then carried along the valley and deposited when the ice melts
- Parallel to ice flow
Medial moraine
- A ridge of moraine down the middle of the valley floor
- When two valley glaciers converge, two lateral moraines combine to form a medial moraine. Material is carried and deposited when melting occurs
- Parallel to ice flow
Terminal moraine
- A ridge of moraine extending across the valley at the furthest point the glacier has reached
- Advancing ice carries moraine forward and deposits it at the point of the maximum advance when it retreats. The up-valley (ice contact) side is generally steeper than the other side as the advancing ice rose over the debris
- Transverse to ice flow
Recessional moraine
- A series of ridges running across the valley behind the terminal moraine
- Each recessional moraine represents a still-stand during ice retreat. They are good indicators of the cycle of advance and retreat that many glaciers experience
- Transverse to ice flow
Drumlins
- Egg-shaped hills of deposited material that occur in swarms (‘basket of eggs’ topography)
- The material is deposited by the glacier, and then moulded into a stream-lined shape when the glacier advances, allowing us to see glacier movement direction
- e.g. Ribble Valley in Lancashire
Till plains
An extensive flat plain of glacial till that forms when a sheet of ice becomes detached from the main body of a glacier and melts in place, depositing the sediments it carried
Lodgement till
Material that has been eroded from the underlying rock by the ice, and is moved by the ice (stuck under the ice)
Ablation till
This was carried on or near the surface of the glacier and was deposited as the glacier melted
Englacial
Situated, occurring, or formed inside a glacier
Subglacial
Situated, or occurring, underneath a glacier or ice sheet
Supraglacial
Situated, or occurring, on top of a glacier
Which landforms can be used to reconstruct former ice extent, movement and provenance?
- Erratics
- Moraines
- Crag and tail
- Drumlin orientation
Environmental value of glacial environments
- The need to maintain a genepool of wild organisms to ensure the maintenance of genetic variety (global seed bank in Svalbard)
- The need to retain wilderness so that animal communities can remain in their natural environment, for example providing sanctuary for the migratory bird and animal communities of the Alaskan North Slope
- To use wholly natural communities that still exist as control systems for comparison with exploited mismanaged systems elsewhere
What % of the world’s people live in polar and mountainous and upland regions?
8%
Economic value of glaciated environments - farming - country examples
- Nepal
- Bolivia (Altiplano)
- Ethiopia (Bale Mountains)
What % of Bolivia’s population lives in the High Andes?
70%
What activities do communities in Bolivia partake in?
- Growing crops: potatoes, quinoa, beans
- Rearing llamas and alpacas
What % of the country’s GDP do communities living in the High Andes in Bolivia earn?
30%
What % of Bolivia’s population are living below the poverty line? How many of these are indigenous Indians living in the Altiplano?
60%, almost all of the %
How has the development of technology helped indigenous communities in the High Andes?
It has provided many opportunities for cottage industries, such as weaving and knitting co-operatives, and ecotourism
What year was the Antarctic Treaty created?
1959
In the International Polar Year of 2007-09, the UN’s Environmental Programme reported that how many countries and how many researchers took part in scientific research in Antarctica?
60 countries, 10,000 people
In the International Polar Year of 2007-09, the UN’s Environmental Programme reported that scientific research cost hoe much in Antarctica?
$1.5 billion
Research projects in Antarctica
- Understanding global change (past, present, future) by looking at ice cores
- Researching ‘life on the edge’ to explore how ecosystems cope with intensely harsh conditions
- Investigating subglacial Lake Vostock and other lakes beneath the ice sheet
- Developing sustainable food webs in the Southern Ocean ecosystem
- Studying the Earth’s upper atmosphere and its links to the lower atmosphere and the Earth’s climate
- Understanding how the Antarctic ice is melting, in terms of scale and pace, using satellites and field data
Farming in alpine areas in developed countries (economic)
- Primarily pastoral because of the above-average precipitation, rugged terrain with steep slopes and stony, shallow soils, which together make cultivation difficult
- In truly Alpine areas, animals are grazed in the summer because meadows are snow free and grass is high quality, and the grass in the valley bottoms can be made into animal feed for the winter
Silviculture
- The planting of trees for commercial forestry
- Carried out by the Forestry Commission and private investors in the UK, with the main type of tree being Sitka spruce (softwood timber, wood pulp, paper)
- Occurs in the uplands due to the struggle of hill farming
