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Glaciers

Glaciers. Quiz. Percentage of Earth’s surface covered by glaciers today. 10%. But, much more extensive in the geologic past. Why are glaciers important. Spectacular landforms preserve information about the atmosphere in bubbles Record evidence of climate change. What is a glacier???.

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Glaciers

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  1. Glaciers

  2. Quiz Percentage of Earth’s surface covered by glaciers today 10% But, much more extensive in the geologic past

  3. Why are glaciers important • Spectacular landforms • preserve information about the atmosphere • in bubbles • Record evidence of climate change

  4. What is a glacier??? • Thick mass of ice and snow • shows evidence of movement • originates on land from • compaction and recrystallization of snow • forms where snow accumulation in winter exceeds summer melt • long lasting

  5. Long lasting? Ok, how long??? Remember the hydrologic cycle Constant motion of water Ocean continent atmosphere if High elevation High latitude Can be thousands of years

  6. Examples of old ice • Greenland Ice Sheet • greater than 25,000 years olf • Antarctic • greater than 100,000 years old • show overhead

  7. Types of glaciers • Two types • Alpine glaciers • Continental glaciers

  8. Alpine Glaciers • Mountain glaciers • Generally confined to mountain valleys • Examples • Alps • Rockies • Iceland • Kimlamanjaro

  9. Continental Glaciers • Ice sheets • massive, thick plates of glacial ice covering an extensive area • examples • Greenland • Antarctica

  10. Speaking of global warming • How much do you think sea level would rise if the Greenland and the Antarctic ice sheets were to melt? 50 - 60 meters

  11. How do glaciers move • Under construction • show the overhead

  12. How does snow turn into glacier ice? • Burial and compaction drives off the air • snow = 90% air • with compaction some of the air is driven off forming • Firn (0.4 gm/cc) • with further burial firm is transformed into • Glacier ice (0.8 gm/cc)

  13. Glacier advance and retreat • Glaciers are always moving downslope • However, sometimes they appear to be • advancing • stationary, or • retreating • How does this work……………………….

  14. To understand glacier advance and retreat we need to understand Mass Balance

  15. Mass Balance • Zone of accumulation • where glacier gains mass • ice • snow • Zone of accumulation • where mass is lost by • evaporation • melting • calving

  16. Show the overhead

  17. Work of glaciers • Erode • transport • deposit

  18. Glacier Erosion • As transporters of sediment, glaciers have no equal • once the debris is eroded it does not settle out • capable of transporting large blocks of material

  19. Glaciers erode in 2 ways • Plucking and quarrying • glacier loosens and lifts rock and incorporates it into the ice • mechanism = ice wedging • abrasion • sediment laden ice acts like a rasp, grinding the rock below • glacier flour = pulverized “powder-like” rock • glacier striations = linear gouges

  20. Erosional features • Continental glaciers - subdued terrain • alpine glaciers - sharp, angular, rugged topography. Glaciers accentuate pre-existing irregularities in the topography

  21. Erosional features to be familiar with • Glacial trough - U-shaped valley • hanging valley • cirque • tarn • fiord • arete • horn • roch mountonee

  22. Show overhead • show slides

  23. Glacial deposits • Drift - general term for all rock and sediment transported and deposited by a glacier Two Categories Till Stratified Drift Deposited directly by glacier ice First carried by a glacier, then transported and deposited by a stream

  24. Landforms composed of till • Eratics - large boulders • Moraines - mount or ridge of till deposited by a glacier • lateral, medial, end, ground • Drumlins - asymmetrical hills of till Direction of ice movement

  25. Show slides • show overhead

  26. Landforms composed of Stratified Drift • Outwash plains - plain of glacial meltwater sediment, usually with braided streams • kettle lake - where block of ice is stranded and buried in till or stratified drift. • Ice contact features • kames - mounts of stratified drift deposited above or marginally to a glacier • eskers - sinuous ridges deposited by streams flowing beneath, in, or on glaciers

  27. Show the overhead

  28. Ice Ages • Ice Age = time of extensive glaciation • Pleistocene Epoch or Pleistocene Ice Age • 2.5 million years ago to 10,000 years ago

  29. The Pleistocene • Not a time of continuous glaciation, but • glacial advances = glacial period • glacial retreat = interglacial • show the overhead • during the last glacial maximum (18,000 yrs ago) • glaciers covered 30% of Earth’s land area • 95% of Canada • Alpine glaciers, • Laurentide Ice Sheet

  30. Other times of extensive glaciation • 250 million years ago • 500 million years ago • 600 million years ago • 2.3 billion years ago

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