Document Type

Article

Publication Title

Journal of Geophysical Research

Publisher

American Geophysical Union

Publication Date

5-10-2001

Volume

106

Issue

B5

Disciplines

Earth Sciences | Geophysics and Seismology

Abstract

Measurements of the deformation of a dense array of boreholes in Worthington Glacier, Alaska, show that the glacier moves with generally bed-parallel motion. Strain in the 200 m deep valley glacier is constant near the surface but follows a nonlinear vertical profile below a depth of about 120 m. By a depth of 180 m, the octahedral strain rate reaches 0.35 yr-1. The three-dimensional velocity field shows spatial complexity with significant deviations from plane strain, despite relatively simple valley geometry in the vicinity of the 6 x 106 m3 study volume. No evidence was found for time-varying deformation or movement along localized shear planes. Observations were made by repeatedly measuring the long-axis geometry of 31 closely spaced boreholes over a 70 day period, and three additional holes after 1 full year of deformation. The holes were spaced 15 to 30 m apart. Installation and measurement of such a large number of boreholes required the development of a semi-automated hot water drilling system that creates straight and vertical boreholes with uniform walls. The equipment and procedures enables borehole profiles to be measured without the use of hole casing. Inclinometry measurements collected in the holes were processed, analyzed for error, and visualized as a fully three-dimensional data set. the new methods offer unique insight into small-scale spatial and temporal variations in the pattern of flow in a valley glacier.

DOI

10.1029/2000JB900440

Comments

An edited version of this paper was published by AGU. Copyright (2001) American Geophysical Union.

Rights

© 2001 by the Amiercan Geophysical Union

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