L2 Glacial Budget


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L2 Glacial Budget

  1. 1. Glacial Budgets Key idea: the amount of ice depends on the glacial budget. This has seen a loss since 1850 and there are seasonal changes due to temperature fluctuations
  2. 2. Objectives: <ul><li>To describe and explain the glacial budget </li></ul><ul><li>To know the terms accumulation and ablation, advance and retreat in a glaciation context </li></ul><ul><li>To give details of a case study of a glacier – recent retreat since nineteenth century: causes and evidence </li></ul><ul><li>To understand the seasonal shifts in temperature and glaciers </li></ul>
  3. 3. The glacier system <ul><li>A glacier behaves as a system. It has inputs, stores, flows and outputs </li></ul>
  4. 4. <ul><li>INPUT </li></ul><ul><li>Precipitation – falling snow in the zone of accumulation , from avalanches or directly onto the glacier </li></ul><ul><li>During fresh snow falls air is trapped between the flakes. </li></ul><ul><li>Under pressure individual particles of ice melt around their edges allowing air to escape. One by one the particles slip forward on the thin film of water and immediately refreeze. In this way the ice of a glacier moves slowly forward in plastic flow at a speed of about 300m per year </li></ul>
  5. 5. <ul><li>Stores – the glacier is a store of water </li></ul><ul><li>Transfers - As more snow falls the underlying layers are compressed into ice. One by one the particles slip forward on the thin film of water and immediately refreeze. In this way the ice of a glacier moves slowly forward under the force of gravity. </li></ul><ul><li>Outputs – outputs from the system. Ablation is the melting of a glacier which produces meltwater </li></ul><ul><li>Evaporation – water liquid -> water vapour </li></ul><ul><li>Slublimation – water solid -> water vapour </li></ul><ul><li>Calving - chunks of ice break away at the snout </li></ul>
  6. 7. The Glacial budget <ul><li>= The balance between the inputs and the outputs </li></ul><ul><li>Accumulation – fresh snowfall, snow from avalanches </li></ul><ul><li>When a glacier melts it is called ablation . </li></ul><ul><li>Accumulation is greater than ablation near the head of a glacier in winter. </li></ul><ul><li>Ablation will exceed accumulation in summer when the temperatures are warmer. </li></ul><ul><li>If ablation exceeds accumulation then the glacier will melt </li></ul><ul><li>If accumulation exceeds ablation then the glacier will extend . </li></ul>
  7. 9. <ul><li>The glacier budget varies between the seasons </li></ul><ul><li>In winter there will be a lot of accumulation with little ablation </li></ul><ul><li>In the summer there is more ablation than accumulation </li></ul>
  8. 10. Tasks <ul><li>Copy the diagram of the glacier system </li></ul><ul><li>Write a sentence to explain why the glacier is described as a system – what are the inputs, stores, transfers, outputs. </li></ul><ul><li>What is meant by ablation and accumulation </li></ul><ul><li>When and where is accumulation highest? </li></ul><ul><li>When and where is ablation highest? </li></ul>
  9. 11. South Cascade Glacier USA NT page 127 Describe the changes that has taken place in the South Cascade Glacier Why has the lower part of the glacier melted more over recent years Do the photos support the concept of global warming? Explain your answer. Source
  10. 13. Homework <ul><li>*****Table pg 127 </li></ul><ul><li>Copy and complete the table by calculating the figures for the net glacier budget column </li></ul><ul><li>Present the data from the table in the form of a line graph </li></ul><ul><li>Describe the trends shown by the graph </li></ul><ul><li>To what extent does the graph support the evidence of glacial retreat indicated by the photos on slide 10 </li></ul>
  11. 14. <ul><li>http://news.bbc.co.uk/player/nol/newsid_4630000/newsid_4635400/4635465.stm?bw=bb&mp=wm&news=1&bbcws=1 </li></ul>