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GLACIOLOGY

GLACIOLOGY. Outlet Glacier Hanging Glacier Alaska Alberta [G415-1] [G415-3]. Definition of a Glacier. A body of firn and ice consisting of recrystallized snow and refrozen meltwater lying wholly or partly on land and showing evidence of present or former flow.

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GLACIOLOGY

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  1. GLACIOLOGY • Outlet Glacier Hanging Glacier Alaska Alberta [G415-1] [G415-3]

  2. Definition of a Glacier A body of firn and ice consisting of recrystallized snow and refrozen meltwater lying wholly or partly on land and showing evidence of present or former flow.

  3. Nature of Glacial IceSources • Precipitation • Avalanches • Rime ice (water vapor frozen on contact) • Superimposed ice : water frozen to Glacier

  4. Nature of Glacial Ice (cont.)Transition of Snow to Glacial Ice - 1 • Process analogous to diagenesis of sediments and metamorphism of sedimentary rock, • Overall conditions for formation: • Sufficient precipitation (need not be large) • Low temperatures (especially in summer)

  5. Nature of Glacial Ice (cont.)Transition of Snow to Glacial Ice - 2

  6. Nature of Glacial Ice (cont.)Transition of Snow to Glacial Ice - 3 Fresh Snow Crystals Firn [NAGT-9] [NAGT-4]

  7. Nature of Glacial Ice (cont.)Transition of Snow to Glacial Ice - 4 [G110-G1]

  8. Nature of Glacial Ice (cont.)Transition of Snow to Glacial Ice - 5 Footnotes:A = in form of hexagonal crystalsB = air expelled as density increasesC1 = melting and refreezing due to pressure-temperature relationshipC2 = melting point varies inversely with pressure.D = ice crystals get larger with time.

  9. Nature of Glacial Ice (cont.)Transition of Snow to Glacial Ice - 6 Other comments:1. With ice near melting point, small increase in pressure causes melting.2. Meltwater flows to area of lower pressure, refreezes.3. This process is called regelation.4. Density of glacial ice < density of ice formed by simple freezing due to trapped air.

  10. Nature of Glacial Ice (cont.)Transition of Snow to Glacial Ice - 7 Snowline Temple Glacier Crevasse[G415-6] [G415-17

  11. Nature of Glacial Ice (cont.)Transition of Snow to Glacial Ice - 7Time and Thickness for Conversions

  12. Nature of Glacial Ice (cont.)Transition of Snow to Glacial Ice - 8

  13. Nature of Glacial Ice (cont.)Properties of Glacial IceNature and Orientation of Ice Crystals Ice Surface Hexagonal crystals • Note glide planes (along which crystals deform) c - axis

  14. Nature of Glacier Ice (cont.) Accumulation Zone

  15. Nature of Glacial Ice (cont.) [G415-G18] [333]

  16. Nature ofGlacial Ice (cont.)Properties of Glacial Ice-2Hardness

  17. Nature of Glacial Ice (cont.)Properties of Glacial Ice (cont.)Crushing Strength

  18. Radiation Reflection Meltwater Firn (6) Conduction (5) Latent Heat (3) Frictional Heat (2) GLACIER GROUND Geothermal Gradient (1) Thermal RelationsHeat Flow Across Glacier’s Boundaries Radiation (4)

  19. Thermal Relations (cont.)Heat Flow Across Glacier’s Boundaries Footnotes for Diagram (1) varies considerably, depending upon geologic conditions (2) depends upon rate of flow (3) very important if surface is often above melting temp. (4) mostly reflected (5) from atmos., firn, snow (Note: could be loss to atmos.) (6) incorporated in glacier (Note: could be warmer or colder)

  20. ICE Coldice: below its pressure-controlled melting point Warmice: above its pressure-controlled melting point (above 0oC ??) GLACIERS Polar: cold ice Temperate: warm ice (except near-surface ice in winter) However, both types can occur in the same glacier. Thermal Relations (cont.)Thermal Classification

  21. Thermal Relations (cont.)Temperature Gradient: Taku Glacier -17°C -10°C 0°C Feb 8 Feb 28 June 4 July 15 65°C 0°C

  22. Thermal Relations (cont.)Temperature Grad.: NW Greenland -50°C -25°C -5°C Winter Mid-Aug. -25°C

  23. Thermal Relations (cont.)Temperature Gradient: Antarctica

  24. Compressive Stress Tensile Stress Glacial MovementStress and Strain External force acting on unconfined soilid sets up 3 types of internal stresses: compressive, tensile, and shearing. Because of stress, changes occur in shape, volume, or both. Shearing Stress

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