Basal conditions and glacier motion during the winter/spring transition, Worthington Glacier, Alaska, U.S.A.

Abstract

ABSTRACT. Observations of the motion and basal conditions of Worthington Glacier, Alaska, U.S.A., during late-winter and spring melt seasons revealed no evidence of a relationship between water pressure and sliding velocity. Measurements included borehole water levels (used as a proxy for basal water pressure), surface velocity, englacial deformation, sliding velocity, and time-lapse videography of subglacial water flow and bed characteristics. The boreholes were spaced 10^15 m apart; six were instrumented in 1997, and five in 1998. In late winter, the water-pressure field showed spatially synchronous fluctuations with a diurnal cycle. The glacier's motion was relatively slow and non-cyclic. In spring, the motion was characterized by rapid, diurnally varying sliding. The basal water pressure displayed no diurnal signal, but showed high-magnitude fluctuations and often strong gradients between holes. This transition in character of the basal water-pressure field may represent a seasonal evolution of the drainage system from linked cavities to a network of isolated patches and conduits. These changes occurred as the glacier was undergoing a seasonal-velocity peak. The apparent lack of correlation between sliding velocity and water pressure suggests that local-scale water pressure does not directly control sliding during late winter or early in the melt season.

Channelized, distributed, and disconnected: subglacial drainage under a valley glacier in the Yukon

“…During this stage, the mean water pressure in the system drops, and the magnitude of diurnal pressure variations increases (see Fig. 12, also Harper et al, 2002). Different parts of bed still exhibit diurnal oscillations but cease to be mutually well-connected, as also observed by Fudge et al (2008).…”

“…Had we sampled the glacier bed differently, we could have had no boreholes showing diurnal oscillations during this period. This widespread drainage shutdown around highly focused drainage subsystems would explain why the end of diurnal oscillations in most boreholes precedes the decline in inferred meltwater supply and proglacial river runoff as observed by Harper et al (2002) and Fudge et al (2005).…”

Subglacial drainage characterization from eight years of continuous borehole data on a small glacier in the Yukon Territory, Canada

“…During this stage, the mean 15 water pressure in the system drops, and the magnitude of diurnal pressure variations increases (see Fig. 11, also Harper et al (2002)). Different parts of bed still exhibit diurnal oscillations but cease to be mutually well-connected, as also observed by Fudge et al (2008).…”

A revised Canadian perspective: progress in glacier hydrology

“…Evolution in drainage morphology is associated with glacier motion (Harper et al, 2002). In fact, Kavanaugh and Clarke (2001) find three periods of strong basal motion at the Trapridge Glacier, following establishment of a well-connected subglacial drainage system.…”