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Glaciers

Glaciers. Glaciers. Slightly more than 2 percent of the world’s water is tied up in glaciers. Antarctic ice sheet Eighty percent of the world’s ice Nearly two-thirds of Earth’s fresh water Covers almost one and one-half times the area of the United States

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Glaciers

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  1. Glaciers

  2. Glaciers Slightly more than 2 percent of the world’s water is tied up in glaciers • Antarctic ice sheet • Eighty percent of the world’s ice • Nearly two-thirds of Earth’s fresh water • Covers almost one and one-half times the area of the United States • If melted, sea level would rise 60 to 70 meters

  3. Glaciers Glacier – a thick mass of ice that originates on land from the accumulation, compaction, and recrystallization of snow Two types of Glaciers: • Valley (alpine) glaciers • Ice sheets

  4. Valley Glaciers • Exist in mountainous areas • Flows down a valley from an accumulation center at its head

  5. Valley Glaciers

  6. Ice Sheets • Exist on a larger scale than valley glaciers • Two major ice sheets on Earth are over Greenland and Antarctica

  7. Ice Sheets • Often called continental ice sheets • Ice flows out in all directions from one or more snow accumulation centers

  8. Continental Glacier

  9. Formation of a Glacier In order for a Glacier to form there needs to be an imbalance in the rate of precipitation and the rate of melting Balance, or lack of balance, between accumulation at the upper end of the glacier, and loss at the lower end is referred to as the glacial budget

  10. Glacial Budget • If accumulation exceeds loss (called ablation), the glacial front advances • If ablation and/or accumulation decreases, the ice front will retreat

  11. Formation of a Glacier Two important zones: Zone of accumulation – the area where a glacier forms Zone of wastage – the area where there is a net loss to the glacier due to

  12. Zone of Wastage Two Processes take place: • Melting • Calving – the breaking off of large pieces of ice (icebergs where the glacier has reached the sea)

  13. Valley Glaciers

  14. Formation of Glacial Ice • Air infiltrates snow • Snowflakes become smaller, thicker, and more spherical • Air is forced out

  15. Formation of Glacial Ice • Snow is recrystallized into a much denser mass of small grains called firn • Once the thickness of the ice and snow exceeds 50 meters, firn fuses into a solid mass of interlocking ice crystals – glacial ice

  16. Formation of Glacial Ice

  17. Movement of Glaciers Two Types of movement: • Plastic Flow • Basal Slip

  18. Plastic Flow • Occurs within the ice • Under pressure, ice behaves as a plastic material - below 50ft

  19. Basal Slip • Entire ice mass slipping along the ground • Most glaciers are thought to move this way by this process

  20. Movement of Glaciers What happens between the surface and a depth of 50 ft? Less Pressure Ice does not behave plastically (does not flow) At shallow depths ice is brittle. Tension from the movement of the more plastic ice below cause cracks to form in the surface. These cracks are called Crevasses

  21. Movement of Glaciers

  22. Rate of movement Average velocities vary considerably from one glacier to another Rates of up to several meters per day Some glaciers exhibit extremely rapid movements called surges

  23. Glaciers

  24. Glacial Erosion Glaciers erode the land in two ways: • Plucking • Abrasion

  25. Glacial Erosion • Abrasion produces: • Rock Flour (Pulverized rock) • Glacial Striations (Grooves or scratches in bedrock)

  26. Glacial Erosion • Erosional features of glaciated valleys • Glacial trough • Truncated spurs • Hanging valleys

  27. Hanging Valley

  28. Glacial Erosion Landforms created by Glacial Erosion • Cirques • Aretes • Horns • Pater noster lakes

  29. Glacial Deposits Drift - sediment deposited by glaciers Types of Glacial Drift: Till - material deposited directly by the ice Stratified Drift - sediments deposited by melt water

  30. Landforms made of Till Moraines - Layers or ridges of till Lateral Moraine Medial Moraine Terminal Moraine (End Moraine)

  31. Landform made of till

  32. Glacial Deposits

  33. Landforms made of Till Drumlins • Smooth, elongated, parallel hills • Steep side faces the direction from which the ice advanced • Occur in clusters called drumlin fields • Formation not fully understood

  34. Drumlin

  35. Stratified Drift Landforms made of stratified drift Outwash plains (with ice sheets) and valley trains (when in a valley) • Broad ramp-like surface composed of stratified drift deposited by meltwater leaving a glacier • Located adjacent to the downstream edge of most end moraines • Often pockmarked with depressions called kettles

  36. Stratified Drift • Ice-contact deposits: • Deposited by meltwater flowing over, within, and at the base of motionless ice • Features include • Kames • Eskers

  37. LI Glacial History

  38. Evidence of LI Glacial Hist. • Terminal Moraines/ Recessional Moraine • Harbor Hills Moraine • Ronkonkoma Moaraine • Kettle Lakes & Kettle holes • Lake Ronkonkoma • Kettle Hole Park • Kames • Bald Hill • Outwash Plains • LI South shore

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