Glaciation Case studies Flashcards
Human Impacts on Periglacial areas
Prudhoe Bay, North Slope Alaska
When were oil deposits found
1968
Size of Prudhoe Bay reserve
3000,million barrels
US oil consumption
6.95 billion barrels annually, 40% imports
Effect of Gravel Pads
Removes load from the river effecting erosion and deposition
Oil extraction Effect on hydrological processes
Glacial Outwash aquifer near palmer, water levels fell by 1m in a radius of 2km from the extraction site
Oil extraction Energy Flows impact
Urban heat island, barrow, 2.2 degrees warmer, maximum difference of 6 degrees leads tpo fewer freeze thaw days (9% reduction) as well as melting of permafrost
Effects on the Landscape Oil extraction
thawing of permafrost, especially from underneath homes, leading to solifluction (downslope movement of the active layer)
Formation of Thermocasts, 5m deep and 1-2km wide
alsases and alsas valleys, gradual depressions 10’s of kilometres in length
Human influence on Glaciated environments
Grande Dixence Dam
Cost of dam construction
1600 million francs
Dam Catchment area
350kmsq including the outlets of 25 glaciers
Pumping to the dam
4 pumping stations and 100km of tunnels
Impact on River channels
Reduced flow of some rivers, the Borgne River has higher concentrations of pollutants at Les Haudere from agricultural and domestic sources du to the reduced flow rate.
Sediment is also trapped behind the dam, meaning that very clear water is returned to the channels, giving the water excess energy and increasing channel erosion.
Lack of discharge in below dam rivers has meant some virtually dry up in the summer, there has been a contraction in the sizes of river channels, the scale of this contraction has increased downstream, the amount of sediment flowing into Lake Geneva has halved.
Val d’Herens, risk of sudden and unexpected flooding when stored water is released.
Rate of deposition in the dam
20-40 cm per year, concentrations of only 20-50 mg per litre behind the dam
Ice Sheet Case study
Minnestota and the Laurentide ice sheet
Most recent advance of the Laurentide ice sheet
100,000 years ago in the Widsconsin glaciation
Lithology of Minesota
Predominantly granite and gneiss, however there is an area of sedimentary rck (shales) that was less resistant to erosio, they formed the ellipsoidal basin that is Lake Vermillion today
Erosional impact of the Laurentide Ice sheet
Wore down many mountains, the highest peak now is eagle mountain at 701m
Depositional impact of the Laurentide Ice sheet
Wadena lobe deposited iron rich sediments and the Wadena drumlin field
Rainy and Superior Lobes left behind a coarse mixture of gabbro and granite
Des Moines Lobe 160 m deep clay rich deposits and end moraine at the Praire Coteau
Pro Glacial Lakes
Water trapped by a Morranic dam and the ice sheet itself, largest was Aggassiz (440,000kmsq and 400m deep.
Glacial river Warren
Drained by Glacial river warren out of traverse gap, forming a wide valley within which the Minnesota river now flows. The original river was 300 ft deep and several miles wide
Changes over time to the landscape
Drumlins and terminal morraines eroded over time, lakes may grow or shrink depending on quantities of precipitationand sedimentation
Snowdonia Location
North Wesr of wales 10km from Bangor, most southerly example of glaciation in the UK, able to sustain glaciers due to altitude and maritime climate (North West)
Last Glacial period in Snowdonia
Devensian period, ended 10,000 years ago, maximum 18,000 years ago, 2000 kmsq of North wales was an accumulation zone
Morraines
Cwm Idwal, Lateral (300 metres long), Terminal and hummocky morraines
Corrie
Cwm Idwal, lithology-tuff and basalt, low altitude (375 m)
Glacial Trough
Nant Francon, step with a drop at Rhaedr Oqwen, truncated spurs such as Clogwyn Y gribin
Roche Moutonne
Nant Francon, just above Rhaedr Ogwen
Ribon Lake
Lyn Ogwen, lies within a glacial hollow, overdeepening caused by the weakness of the lithology, thickness of ice and gradient of the valley
Pyramidal Peak
Snowdon Yr Wyddfa, 10 cirques, two largest face North West (Clogwyn and D’ur Addu)
Arete
Crib Goch, formed due to perpendicular flow of the cirque glaciers in Cwm Glas and Cwm Uchaff to Cwm Gaslyn, made of tuff
Location as an influence to glaciation
Snowdon-Wide base 80km2 not overrun by ice sheet and formed by alpine glaciation
Cwm Idwal located at lowest point of the Glyderau range so ice spilled over from the Lanberis pass, additionally deepened by the rotaitional flow of the Cneiford Ice fall
Aspect as an influence to glaciation
Corries surrounding Snowdon, deapest face North West (Clotacular and pronounced back wallsgwyn and Du’addu) leading to more spec
Lithology
Snowdon-Tuff, hard rock to support dramatic features
Lithology of ogwen valley as well as tributary glaciers and compressional flow lead to over deepening
Lithology at Rhaedr Ogwen, more resistant
Cwm Idwal lies on a line of geological weakness (syncline)
Effect of weathering over time in snowdonia
Steepening of back walls -Devils Kitchen and Idwal slabs
Aretes becoming narrower (scree slopeson the side of crib goch
Sides of Nant Francon Valley also steepened
Sedimentation
Nant Francon valley used to hold a ribbon lake, however it was infilled by sedimentation from neighbouring corries such as cwm idwal
Filling of Lakes
Lyn Ogwen-Post glacial feature, filled by melt water and rainfall. Llyn Idwal also filled
