HR: 0830h
AN: C31B-0398    [PDF]
TI: Post-surge distribution of warm-ice at Bakaninbreen, Svalbard from ground-penetrating radar
AU: * Murray, T
EM: t.murray@geog.leeds.ac.uk
AF: Faculty of Earth and Environment, University of Leeds, Leeds, LS2 9JT United Kingdom
AU: Woodward, J
AF: Division of Geography and Environmental Management, University of Northumbria, Newcastle upon Tyne, NE1 8ST United Kingdom
AU: Barrett, B
AF: Faculty of Earth and Environment, University of Leeds, Leeds, LS2 9JT United Kingdom
AU: Stuart, G
AF: Faculty of Earth and Environment, University of Leeds, Leeds, LS2 9JT United Kingdom
AB: Bakaninbreen, a 17-km long glacier in southern Svalbard, underwent a prolonged surge during 1985--95. The surge front, $\sim$50 m high, propagated progressively downstream, and by 1995 had halted $\sim$1.7 km from the glacier margin. Ground-penetrating radar (GPR) surveys located just downstream of the front suggested that ice and bed were at temperatures below the pressure melting point; surveys located just upstream of the surge front showed warm ice at the bed (at the pressure melting point), and zones of scattering at the sides of the glacier interpreted as warm ice in shear zones. These results have been used to suggest that the surge involved a thermally regulated soft bed mechanism, with the rate of propagation of the front controlled by friction at the margins and the rate of warming of the bed. However, the interpretation at Bakaninbreen was based on GPR and seismic surveys located within 1 km of the surge front. GPR surveys further upstream were conducted to identify spatial variation in the structure and thickness of the scattering zones; to image any marginal shear zones; to attempt to differentiate between water and sediment inclusions as causes for the scattering; and to assess the water content of any warm ice. Twenty-seven 100 MHz crossglacier common offset (CO) radar lines were collected, typically 1 km in length, as well as shorter multi-frequency and multi-polarisation CO and common midpoint (CMP) surveys. The distribution of scattering does not simply reflect shear margins at the sides of the glacier, nor is it confined to the areas of thickest ice. Two unexpected attributes of the regions are: (i) their distribution changes markedly over relatively short distances up and downstream ($\sim$200 m); (ii) some are isolated both from the glacier bed and the surface. The CMP surveys show the water content of the ice would be $\sim$3-4% dependent on the inclusion model used. Warm ice could result from (1) strain heating during fast flow; (2) water ``injection'' from basal or surface crevasses; or (3) changes in the melting point with depth. Sediment can be added to the ice from the glacier bed or from surface sources. We assess which of these best explains the distribution of scattering within the glacier.
DE: 1827 Glaciology (1863)
DE: 1863 Snow and ice (1827)
SC: Cryosphere [C]
MN: 2003 Fall Meeting