Key Idea 2: Quaternary Deposits/Landforms in Britian

• • ice age when th is permanent snow over the poles (currently in Pleistocene/Holocene ice age; started 2.5Ma at start of Quaternary) + 5th known ice age in history
  • earth transitioned in Holocene 11,000 years ago during 'Flandrian Transgression'; currently within Flandrian Interglacial (significant retreat of ice sheets rapidly occured leading to mass extinctions)
• Pleistocene Glaciers:

  • currently 10% (14.9million km$^2$) covered by glaciers; during Quaternary, glaciers covered up to 30% of earth's surface - sea leevel rose 120m in 18,000 years of glacial retreat
• Glacier - a tongue of ice that moves slowly downhill along a valley (and replenished at its source).

  • Alpine Glacier - melt/retreat in summer + melting ice helps glacier move and erode/transport/deposit material + soruces of many great rivers.
  • Polar Glacier - located in regions where temperatures don't rise above freezing, so little melting/glacier movement much slower.
• Ice Sheet - a very large body of ice that can survive long periods of warming; unaffected in interglacials and expand towards equator in glacials.

  • nunataks; high peaks of mountains sticking out through ice sheets + ice sheets not constrained by underlying topography (can flow over mountains, but slowly)
• Glacial Budget/System:

  • Inputs - snow, weathered material (rock/boulders) + avalanches.
  • Outputs - meltwater, moraines (weathered, worked material) + icebergs + some snow from evaporation.

  
• Basal Slippage (glacier movement):

  • if glacier moves, this raises temperature of base ice through pressure/friction; the basal ice then melts (pressure melting point is -2$^oC$) allowing ice to slip more easily over its base
  • potential to move 2-3m/day and pick up material which could erode its bed + related to regelation (melting under pressure and freezing again when pressure is reduced)
• Erosional Processes:

  • Plucking - where moving ice freezes to the broken-up rock surface and plucks up loose material (becomes part of glacier contributing to abrasion).
  • Abrasion - steady supply of abrasive material by downward transport of rock debris to basal layer of glacier; rocks grind away/erode surface (glacier ice must be thick to be heavy enough to erode surface).
• • Supraglacial debris - carried on glacier surface as lateral/medial moraines + material that has fallen onto glaciers from surrounding valley sides; in summer, small load carried by meltwater streams falls down crevasses.
  • Englacial debris - material carried within the glacier; may have been on surface but buried by snow/fallen down crevasses.
  • Subglacial debris - moved along floor of valley by ice or meltwater streams formed by pressure melting.
• Frost-shattering

  • produces loose material that may fall from valley side onto glacier edges to form lateral moraines, be covered by snowfall, or fall down crevasses/transported by englacial debris
  • some material may be added to rock loosened by frost action to form basal debris as climate deteriorated
• Abrasion - sandpappering effect of angular material embedded in the glacier as it rubs against the valley sides and floor; produces smooth, gently sloping landforms.
• Plucking - glacier freezes onto rock outcrops then ice movement pulls away masses of loosened material, creating jagged featured landscape - material loosened by:

  • pressure melting point produces sufficient meltwater for frost shattering to break up the ice-contact rock
  • water flowing down bergschrund (large crevasse found near glacier head)/crevasses will freeze onto rock surface
  • removal of bedrock layers by glacier causes release in pressure/enlarging of joints in underlying rocks (pressure release)
• • compressing flow; reduction in gradient of valley floor, ice deccelerates and becomes thicker (associated with abrasion)
  • extending flow; valley gradient steepens, ice accelerates and becomes thinner (associated with plucking)

  
• Glacier Movement:

  • Creep - pressure increase if obstacle in path of glacier; as stress builds up, ice behaves plastic and flows around/over the obstacle + lower the temperature, the greater pressure needed for this process to occur (less likely in cold glaciers).
  • Surges - results of excessive build up of subglacial meltwater reservoirs/occur when rock avalanches fall onto glacier surface (or by earthquake); glacier moves forward (up to 300m/day) + sudden release of meltwater causes severve flooding.
• Glacier Cross Section:

  A) meltwater

  B) outputs

  C) inputs

  D) equilibrium

  E) ablation