In situ measurements of till deformation and water pressure
Authors: Truffer, Martin; Harrison, William D.
Source: Journal of Glaciology, Volume 52, Number 177, March 2006 , pp. 175-182(8)
Publisher: International Glaciological Society
Abstract:A newly developed hammer was used to insert two autonomous probes 0.8 m and 2.1 m into clast-rich subglacial till under Black Rapids Glacier, Alaska, USA. Both probes were instrumented with a dual-axis tilt sensor and a pore-water pressure transducer. The data are compared to a 75 day record of surface velocities. Till deformation at depth was found to be highly seasonal: it is significant during an early-season speed-up event, but during long periods thereafter measured till deformation rates are negligible. Both tilt records show rotation around the probe axis, which indicates a change in tilt direction of about 30°. The tilt records are very similar, suggesting spatial homogeneity on the scale of the probe separation (4 m horizontal and 3.3 m vertical). There is evidence that during much of the year sliding of ice over till or deformation of a thin till layer (<20 cm) accounts for at least two-thirds of total basal motion. Basal motion accounts for 50-70% of the total surface motion. The inferred amount of ice-till sliding is larger than that found at the same location in a previous study, when surface velocities were about 10% lower. We suggest that variations in ice-till coupling account for the observed variations in mean annual speed.
Document Type: Research article
Publication date: 2006-03-01
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