Glaciers

• What are glaciers?


  masses of ice (and debris) compressed over many years which are continually changing
• What percentage of the worlds land areas do glaciers occupy?

  10%
• Accumulation zone of a glacier


  where inputs exceed outputs
• Why is there an accumulation zone

  o More precipitation at higher altitudes (the orographic effect), mainly snow

  o New snow is highly reflective, so it absorbs less heat and melts more slowly

  o Strong winds at higher altitudes blow snow into hollows and basins where it can accumulate

  o Temperatures are low, so sublimation (solid to vapour) is low and meltwater is likely to refreeze
• Accumulation


  The net gain in an ice mass
• Firn


  A dense, icy pack of old snow

  
• Sublimation


  solid to gas
• Where is the Ablation Zone?

  o Lower altitudes

  o Towards the snout of a glacier
• ablation zone


  Outputs exceed inputs

  
• why is there an ablation zone?

  o Less snowfall

  o Temperatures are higher
• Ablation


  the process of wastage of snow or ice, especially by melting

  
• Equilibrium (firn) line


  The dividing line between the two zones

  
• Glacial Budget/net balance


  The NET balance of accumulation and ablation. It compares the the amount of snow accumulation on the ice sheet and the amount of meltwater leaving the ice sheet. it is measured on a monthly basis.
• Steady State


  When amounts of accumulation and ablation are equal over the course of a year

  As a result, the snout of the glacier will remain stationary, but the mass of ice will still be passing through
• Glacial surge/advance


  Glaciers may take many years to react to changes in accumulation or ablation but where snowfall is exceptionally heavy the glacier may react quickly and surge forward
• Glacier Speed


  o Extremely variable

  o Fastest up to 50m and 400m per year

  o Flow rates of 1000m a year or more in large ice streams in Antarctica and outlet glaciers in Greenland
• How does climate affect a glaciated landscape?

  -Wind - aerolean processes =erosion, transportation and deposition

  -Precipitation - provides inputs

  - Temp. - Above 0C, ice starts to melt and adds to outputs.
• How does geology affect a glaciated landscape?

  lithology and structure
• Lithology


  physical and chemical characteristics of rock
• weak lithology means?


  little resistance to erosion as bonds between particles are weak
• strong lithology means?


  highly resistant due to dense interlocking crystals
• structure of rocks?


  jointing / cracks = increased permeability
• How does latitude affect a glaciated landscape?

  Locations at high latitudes tend to have cold, dry climates with little seasonal variation in precipitation

  At lower latitudes, places with high altitudes are characterised by dynamic valley glaciers
• How does altitude affect a glaciated landscape?

  Lower latitudes and higher altitudes create dynamic valley glaciers

  Temperature decreases with altitude at a rate of approximately 0.6C/100m
• How does relief affect a glaciated landscape?

  The steeper the landscape, the greater the resultant force of gravity and the more energy a glacier will have to move downslope
• How does aspect affect a glaciated landscape?

  If a slope faces away from the sun, temperatures remain below zero for longer so less solar energy is received and more melting occurs
• Diagenesis


  Each new fall of snow compresses and compacts the layer beneath, causing air to be expelled and converting low density snow into higher density ice
• diagenesis process


  1. Fresh snow falls

  2. Snow that survives one summer is called firn

  3. With further compaction by subsequent years of snow fall, it becomes glacier ice
• valley glacier


  A long, narrow glacier that forms when snow and ice build up in a mountain valley

  
• ice sheet


  a very large, thick mass of glacial ice flowing outward in all directions from one or more accumulation center(s). over 50000km2

  
• Ice Cap


  a covering of ice over a large area, especially on the polar region of a planet. under 50000km2
• Ice Shelf


  a massive extension of glacial ice over the sea, often protruding hundreds of miles

  
• Piedmont Glacier


  glacier that reaches a valley floor and spreads out in a bowl shape

  
• Corrie/ Cirque/ Cwms Glacier


  Named after the bowl-like hollows they occupy

  Found on high mountain sides and tend to be wide rather than long

  
• Niche Glacier


  very small glacier that occupies gullies and hollows on north-facing slopes (northern hemisphere); may develop into cirque glacier if conditions are favorable.
• WB glacier - surface melting


  In summer, rises above 0C allowing some surface melting
• CB glacier - surface melting

  Limited summer melting
• WB glacier - basal temp

  Basal temperatures at or above pressure melting point
• CB glacier - basal temp

  Basal temperatures below pressure melting point so movement is limited
• WB glacier - erosion


  Landforms of erosion

  Greater erosive power