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Glacier Basics

Glacier Basics. An introduction to where, how, and why glaciers form. What is a glacier?. Large mass of moving ice that originated on land from accumulation, compaction, and recrystallization of snow When snow is added to a glacier faster than ice and snow melt, the glacier gets larger

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Glacier Basics

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  1. Glacier Basics An introduction to where, how, and why glaciers form

  2. What is a glacier? • Large mass of moving ice that originated on land from accumulation, compaction, and recrystallization of snow • When snow is added to a glacier faster than ice and snow melt, the glacier gets larger • Largest fresh-water reservoir on Earth (75% of world’s fresh water) • Two main types • Continental glaciers /ice sheets • Alpine/valley glaciers

  3. Continental Glaciers • Massive sheets of ice that may cover millions of square kilometers, that may be thousands of meters thick, and that are not confined by surrounding topography • Are also called ice sheets

  4. Alpine Glacier • Narrow, wedge-shaped mass of ice that forms in a mountainous region that that is confined to a small area by surrounding topography

  5. Where are glaciers found? • Glaciers are found on every continent except Australia • Found in polar regions and mountain ranges (and other planets) • Usually glaciers start at higher elevations and flow downward and outward Hugo Ahlenius, UNEP/GRID-Arendal, overview of world glaciers and ice caps, UNEP/GRID-Arendal Maps and Graphics Library, (Accessed 22 June 2009)

  6. Glaciers form wherever more snow accumulates in the winter than melts in the summer. • Glaciers form above the snowline or lower limit of perennial snow in the zone of accumulation. • Glaciers move downhill in response to gravity • Glaciers melt or sublimate in the zone of wastage/ablation • Crevasses are large cracks which reach the glacier surface and form by a number of ways Glacier formation

  7. Glacial Movement • Glaciers move in 2 ways: • Basal Slip: simple response due to gravity whereby the ice moves downhill over bedrock and slipping over a thin layer of water. • Internal Plastic Flow: If you stack a LOT of ice, the pressure increases and the ice behaves plastically, meaning that the lower layers will start to deform. Flow in a glacier is smooth at depth, but in the top ~50 m ice is brittle and cracks

  8. Glacial erosion • Rate of glacial erosion depends on • Rate of glacial movement • Ice thickness • Underlying rock characteristics

  9. Glacial erosion • Plucking • Deep depression in rock when moving glacier loosens and dislodges rock from bedrock at base or side of glacier • Sediment carried and deposited by glaciers is called glacial drift • Abrasion • Caused by glacial flow • Striations form

  10. How do glaciers change a landscape? Lateralmoraines Cirque Horn Arête Grosser Aletschgletscher (Bernese Alps), Dirk Beyer Mainglacier Medialmoraines

  11. How do glaciers change a landscape?Erosional Features Horns Arête Cirque Tarnlake Hangingvalley Truncated spur Paternoster lakes U-shaped valley Erosional features of a glaciated valley, DK www.wiredantarctica.com

  12. Glacier anatomy: Alpine Glaciers Hanging Valley: Form where a higher elevation glacier flows into a larger glacier that has a deeper canyon Hangingvalley U-shaped valley Yosemite Valley www.wiredantarctica.com

  13. Crevasses • Form by: • Two glaciers colliding • Accelerations in glacier speed • Changes in underlying topography

  14. Glacial Erosion - Landforms • Cirque- Moving glacier pulls blocks of rock from the floor of the valley and create a bowl shaped depression

  15. Glacial Erosion - Landforms • Arête- Sharp, jagged ridge forms between cirques

  16. Glacial Erosion - Landforms • Horn- When several arêtes join, they form a sharp, pyramid-like peak

  17. Glacial Erosion - Landforms • Fjord- forms where a glacier has eroded a valley into the sea. When glacier retreats, the sea fills in.

  18. Glacial Deposition - Landforms • Erratic- Large boulders carried a long distance from their original location

  19. Glacial Deposition - Landforms • Moraines- The debris that glacier grind up, carry, and push out in front of it

  20. Glacial Deposition - Landforms • Drumlins- long, tear shaped mound

  21. Glacial Deposition - Landforms • Braided Streams- multiple small, shallow channels

  22. Glacial Deposition - Landforms • Kettles- occurring as the result of blocks of ice caving in

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