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Surging Glaciers

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  1. Surging Glaciers Heike Bischof 6/8/2003 Trapridge Glacier, Yukon

  2. Seminar Outline • Definition and Characteristics • The Surge Cycle • Example: Variegated Glacier • Drainage Systems and Glacier Flow • Two mechanisms based on two case studies

  3. What are surging glaciers? • Surge behaviour: • “multi-year oscillation between extended periods of normal motion and brief periods of comparatively fast motion.” (C.F.Raymond, 1987)

  4. Characteristics • Globally small percentage (5%) • Represtentation in varying climates • Various types of glaciers can surge • Surging glaciers surge in periodic cycles • Clustered in some regions, mainly Alaska, Yukon, British Columbia, Iceland, Svalbard (Arctic), Pamir • also: Antarctica, Spitsbergen, California, Andes • Artic: Ellesmere and Axel Heiberg Island, • Asia: Karakoram Mountains, Caucasus, Tien Shan

  5. The Surge Cycle (Quiescent Phase) • Quiescent phase longer than active phase (up to 500y) • Filling and thickening of reservoir area • Increase in creeping in reservoir area • Stagnation and thinning in receiving area • Steepening front at Dynamic Balance Line (DBL) (Raymond 1987) Trapridge Glacier, Yukon

  6. The Surge Cycle(Active Phase) • Ice velocity increase of one magnitude • Ice displacement 1/10 of glacier length • Ice propagates in kinematic waves from upper to lower glacier resulting in • large elevation drops and rises • (100-200m) • Surge usually coincides with • advance of the glacier terminus • (steep, bulging front) Hubbard Glacier

  7. 1982/3 Surges of Variegated Glacier…continued (Benn and Evans, p.173)

  8. 1982/3 Surges of Variegated Glacier (Kamb et a., 1985) • The surge took place in different phases over 2y • Outburst floods coincide with slowdowns in surge activity • At km 7: Ice thinning of 50m • At km 16: Ice thickening of 100m

  9. Variegated Glacier Presurge (July ‘82) During Surge (July ’83)

  10. How do glaciers move? • - creeping(no water) -internal deformation of the ice( “ ) - bed deformation(subglacial water) • basal sliding(subglacial water) high speeds are achieved through slidingon a water lubricated base • Boreholes measurements: high water pressure coincides with an increase, floods with slowdowns in flow velocity during the active surge phase

  11. Subglacial Drainage Systems • Depends on water discharge, temperature distrubution , ice-bed interface, permeability, topography, rigidity of bed • Discrete • water transported in a few channels • organised drainage system, large volume of water necessary • Distributed systems • water transported over large proprotion of the bed • unorganised drainage system, little meltwater

  12. Linked Cavity System(Variegated Glacier) • Summer meltwater is stored in cavities during winter • Spring ablation adds extra water establishing channels between cavities • Water drainage is slowed down as water is stored in cavities • Injection of tracer dye during surge • average flow speed 0.02m/sec requires the tunnel to be 1mm in diametre • Measured discharge required for diametre of 4.5m

  13. Sliding on ‘hard beds’ (Kamb et al.,1985) • Water pressure in cavities rises • When the water pressure comes close to, or exceeds the overburden pressure, the glacier floats on a layer of water • Sliding occurs • When the water pressure falls in cavities, the glacier contacts the bed • Sliding stops

  14. Sliding on ‘soft beds’(Clarke et al., 1984) • Traprigde Glacier is generally frozen to its bed, but at pressure melting point in upglacier-area • A drainage system is established in a permeable bed during the quiescent phase • During a surge, the drainage system might be destroyed temporarily, allowing pore pressure to build up and inducing shear failure of the substrate => Sliding/ Subsole deformation

  15. Discussion ? How does inconsistency of flow velocity evolve? • ? Why do only certain glaciers surge? • Relationship to bedrock, topography • ? Why are surging glaciers clustered in some areas? • ? Only few studies have been undertaken on subpolar and cold based glaciers

  16. References • Benn, D.I. and D.J.A. Evans (1998) Glaciers and Glaciation, Oxford Universtiy Press, Oxford. • Bennet, M.R. and N.F. Glasser (1997) Glacial Geology – Ice Sheets and Landfroms, John Wiley and Sons, Chichester. • Clarke, G.K.C. et al. (1984) “Flow, thermal structure, and subglacial conditions of a surge-type glacier” in Can.J.Earth.Sc.21 pp.232-240. • Fatland, D.R. and C.S. Lingle (2002) “In SAT abservations of the 1993-1995 Bering Galcier(Alaska U.S.A.) surge and a surge hypothesis” in J.Glaciol.48 pp.439-451. • Kamb, B. (1985) “Glacier Surge Mechanism: 1982-1983 Surge of Variegated Glacier, Alaska” in Sc.227 pp.469-479. • Kamb, B. (1987) “Glacier Surge Mechanism Based on Linked Cavity Configuration of the Basal Water Conduit System” in J.Geophysical Research 92 pp.9083-9100. • Meier, M.F. and A. Post (1969) “What are glacier surges?” in Can.J.Earth Sc. 6 pp.807-17. • Raymond, C.F. (1987) “How do glaciers surge? A Review?” in J. Geophysical Research 92 pp.9121-9134.