glaciation

• Glacier

  A large system of ice and snow
• Conditions needed for glaciers to form

  • High latitude altitudes
  • Lots of snowfall and cool summers
• Glaciers are found close to the poles and high on mountains
• Glaciers across the world are shrinking
• Glacier mass balance


  The difference between inputs (accumulation) and outputs (ablation)
• Glaciers are a moving block of ice
• Importance of glaciers


  • Provide drinking water, tourism, hydroelectric power, and influence agriculture and crops
• Glacier movement


  Due to the weight of gravity, moving 25cm a day
• Glacier mass balance


  1. Positive balance: inputs > outputs, glacier grows

  2. Negative balance: inputs < outputs, glacier retreats
• Glacier mass balance zones

  1. Zone of accumulation: higher altitude, more inputs

  2. Zone of ablation: lower altitude, more outputs

  3. Zone of equilibrium: inputs = outputs
• Inputs to a glacier


  • Precipitation
  • Deposition
  • Avalanche debris
  • Wind-blown snow
  • Rock debris
• Outputs from a glacier


  • Sublimation
  • Meltwater
  • Calving
  • Solar energy
  • Rock debris
  • Wind-blown snow
• Firn snow


  Compact snow that has been through one winter's freezing and melting
• Glacier ice


  Composed of ice crystals compressed by air pockets
• After many years, the air is compressed out and glacier ice forms
• Increase in global temperatures

  Hotter summers and milder winters, preventing ice buildup
• Glaciers have a high albedo


  Less high albedo areas and more low albedo ocean, leading to more absorption of UV radiation
• Milankovitch cycles


  Variations in the Earth's orbit, tilt, and wobble that cause changes in insolation
• Milankovitch cycle components

  • Eccentricity of orbit (100,000 years)
  • Axis tilt (41,000 years)
  • Precession (23,000 years)
• Cooling leads to further cooling


  Increased snow and ice cover raises albedo, reflecting more solar radiation
• Warming leads to further warming

  Decreased sea ice and snow cover lowers albedo, absorbing more solar radiation
• Causes of short-term climate change

  • Solar forcing
  • Volcanic eruptions
  • Anthropogenic factors
• Present-day glacier distribution covers just over 10% of the Earth's land surface
• During the Devensian glacial, glaciers covered around 40% of the Earth's land surface
• Where glaciers are found

  • High latitude
  • High altitude
• Cryosphere


  Parts of the Earth's surface and atmosphere that are below 0°C for part or all of the year, including sea ice, permafrost, and snow cover
• Factors affecting glacier morphology

  • Climate
  • Topography
• Types of ice masses

  • Ice sheets
  • Ice caps
  • Ice fields
  • Valley glaciers
  • Cirque glaciers
  • Ice shelves
• Pressure melting


  Ice will melt at temperatures below 0°C due to the pressure from the weight of the overlying ice
• Deformation of ice


  Ice moves in response to stress, causing fracturing and crevasses
• Slope gradient


  Increased slope angle leads to faster ice movement, decreased slope leads to compression
• Velocity of ice movement

  Ranges from 3-500m per year, with warm-based glaciers moving faster than cold-based glaciers
• Glacial deposits are formed by the action of ice, water or wind.
• Surge conditions


  • Water build up under the glaciers during a phase of rapid glacier flow
  • Increase and unclening of ice in the accumulation zone
• Subglacial meltwater channels


  1. Closed during summer when the weight of ice accumulation is so great

  2. Open during winter when deglacial meltwater is present
• Subglacial water pressure


  Supports the overlying ice, lubricating it and causing the glacier to flow more readily
• Abundant subglacial water


  Increases the pore water pressure, contributing to the rapid surge
• The surge cycle can occur as frequently as every 10-20 years
• Weathering


  The breakdown of rock where it is located, e.g. through freeze-thaw and carbonation
• Erosion


  The removal of rock by ice, water, wind or gravity