IngentaConnect Localized basal motion of a polythermal Arctic glacier: McCall Gl...

Authors: Pattyn, Frank; Nolan, Matt; Rabus, Bernhard; Takahashi, Shuhei

Source: Annals of Glaciology, Volume 40, Number 1, January 2005 , pp. 47-51(5)

Publisher: International Glaciological Society

Abstract:

We analyzed the ice flow of McCall Glacier, Alaska, USA, by numerical glacier modeling and radio-echo sounding (RES). Model experiments were carried out with a higher-order numerical ice-flow model, and results were validated with measurements of annual ice velocities and compared with previous estimates of ice-flow dynamics. During the 2003 summer campaign, detailed RES measurements were carried out along the central flowline of the ablation area with a 5 MHz (central frequency) ice-penetrating radar, where 10 m ice temperatures are approximately −7.5°C. The bed reflection power (BRP) beneath this central flowline abruptly increases at one location area, followed by a slow decrease down-glacier. The model experiments show that basal sliding (<50%) is necessary to match the observed annual mean surface velocities in the area that is characterized by high BRP values. However, when thermomechanical effects are taken into account, a temperate basal ice layer is apparent in the ablation area, which locally softens the ice and can explain to a certain extent the anomalous flow field. The model results confirm that the present temperature field is a remnant of a larger glacier geometry that was near steady state before the onset of enhanced surface thinning in the 1970s.

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Localized basal motion of a polythermal Arctic glacier: McCall Glacier, Alaska, USA