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Tschetter, T.J., 2008

Seasonal evolution of a glacial hydrologic system: Observations of borehole water levels from the Bench Glacier, Alaska

Bibliographic Reference

Tschetter, T.J., 2008, Seasonal evolution of a glacial hydrologic system: Observations of borehole water levels from the Bench Glacier, Alaska: University of Wyoming, Laramie, M.S. thesis, iii, 85 p., (some color) illust., map.

Abstract

Observations of borehole water-level fluctuations were recorded on the Bench Glacier, Alaska, for a period of more than 3 years. These observations indicate that large diurnal water level fluctuations are common during the first summer following borehole installation, but not in later summer melt seasons. Four observations common to many of the boreholes are identified: (1) large diurnal fluctuations in borehole water level are in phase with and have similar shape to the diurnal fluctuations in outlet stream discharge; (2) large diurnal water-level fluctuations are terminated by water-level rises to an elevated and slightly or non-varying water level; (3) the small fluctuations that occur at the elevated water level are generally out of phase with other large fluctuations and the outlet stream discharge; and (4) diurnal fluctuations recorded during the second and subsequent years are smaller and show a greater distribution of peak times relative to the peak time of the outlet stream discharge. The large diurnal fluctuations are interpreted to result from discharge forcing in subglacial drainage conduits. Termination of large diurnal fluctuation results from local disconnection of a borehole from the subglacial drainage network. Small diurnal fluctuations that are out of phase with the outlet stream discharge result from pressure fluctuations in the unconnected system; two potential forcing mechanisms for these small fluctuations are presented. Boreholes do not preferentially reconnect to the conduit drainage system in years following the year of installation.

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