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

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

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)

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

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

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 ( m)  Surge usually coincides with advance of the glacier terminus (steep, bulging front) Hubbard Glacier

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

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

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

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 sliding on a water lubricated base  Boreholes measurements: high water pressure coincides with an increase, floods with slowdowns in flow velocity during the active surge phase

Subglacial Drainage Systems 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

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

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

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

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

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 Fatland, D.R. and C.S. Lingle (2002) “In SAT abservations of the Bering Galcier(Alaska U.S.A.) surge and a surge hypothesis” in J.Glaciol.48 pp Kamb, B. (1985) “Glacier Surge Mechanism: Surge of Variegated Glacier, Alaska” in Sc.227 pp Kamb, B. (1987) “Glacier Surge Mechanism Based on Linked Cavity Configuration of the Basal Water Conduit System” in J.Geophysical Research 92 pp Meier, M.F. and A. Post (1969) “What are glacier surges?” in Can.J.Earth Sc. 6 pp Raymond, C.F. (1987) “How do glaciers surge? A Review?” in J. Geophysical Research 92 pp