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Articles 121 - 125 of 125
Full-Text Articles in Physical Sciences and Mathematics
Spatial Variability In The Flow Of A Valley Glacier: Deformation Of A Large Array Of Boreholes, Joel T. Harper, Neil Humphrey, W. Tad Pfeffer, Snehalata V. Huzurbazar, David B. Bahr, Brian C. Welch
Spatial Variability In The Flow Of A Valley Glacier: Deformation Of A Large Array Of Boreholes, Joel T. Harper, Neil Humphrey, W. Tad Pfeffer, Snehalata V. Huzurbazar, David B. Bahr, Brian C. Welch
Geosciences Faculty Publications
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 …
In Situ Stress Tensor Measured In An Alaskan Glacier, W. Tad Pfeffer, Neil Humphrey, B. Amadei, Joel T. Harper, J. Wegmann
In Situ Stress Tensor Measured In An Alaskan Glacier, W. Tad Pfeffer, Neil Humphrey, B. Amadei, Joel T. Harper, J. Wegmann
Geosciences Faculty Publications
An experimental program at Worthington Glacier, Alaska, U.S.A., has yielded the first in situ measurements of the full stress tensor in glacier ice. Measurements were made with an array of stiff (low-compliance) normal-force sensors frozen into a borehole at 120 m depth. Freezing in temperate ice was accomplished by a down-hole heat exchanger which extracted heat at the rate of 15 W. Under slowly varying stress conditions, relaxation of stress anomalies by viscous creep following drilling of the hole and installation of the sensors allows for equilibration of measured stresses with far-field stresses. Equilibration of local and far-field stresses was …
Crevasse Patterns And The Strain-Rate Tensor: A High-Resolution Comparison, Joel T. Harper, Neil Humphrey, W. Tad Pfeffer
Crevasse Patterns And The Strain-Rate Tensor: A High-Resolution Comparison, Joel T. Harper, Neil Humphrey, W. Tad Pfeffer
Geosciences Faculty Publications
Values of the strain-rate tensor represented at a 20 m length scale are found to explain the pattern and orientation of crevasses in a 0.13 km2 reach of Worthington Glacier, Alaska, U.S.A. The flow field of the reach is constructed from surveyed displacements of 110 markers spaced 20-30 m apart. A velocity gradient method is then used to calculate values of the principal strain-rate axes at the nodes of a 20 m x 20 m orthogonal grid. Crevasses in the study reach are of two types, splaying and transverse, and are everywhere normal to the trajectories of greatest (most …
Mapping Subglacial Surfaces Of Temperate Valley Glaciers By Two-Pass Migration Of A Radio-Echo Sounding Survey, Brian C. Welch, W. Tad Pfeffer, Joel T. Harper, Neil F. Humphrey
Mapping Subglacial Surfaces Of Temperate Valley Glaciers By Two-Pass Migration Of A Radio-Echo Sounding Survey, Brian C. Welch, W. Tad Pfeffer, Joel T. Harper, Neil F. Humphrey
Geosciences Faculty Publications
High-resolution maps of the glacier bed are developed through a pseudo-three-dimensional migration of a dense array of radio-echo sounding profiles. Resolution of three-dimensional maps of sub-glacial surfaces is determined by the radio-echo sounding wavelength, data spacing in the field, and migration. Based on synthetic radio-echo sounding profile experiments, the maximum resolution of the final map cannot exceed one half-wavelength. A methodology of field and processing techniques is outlined to develop a maximum-resolution map of the glacier bed. The field and processing techniques valley glacier in south-central Alaska. The field techniques and the processing steps used on the glacier result in …
The Neocene Lake Beds Of Western Montana And Descriptions Of Some New Vertebrates From The Loup Fork, Earl Douglass
The Neocene Lake Beds Of Western Montana And Descriptions Of Some New Vertebrates From The Loup Fork, Earl Douglass
Graduate Student Theses, Dissertations, & Professional Papers
Since coming to Montana in the spring of 1894 I have spent rnuoh of ay time in studying the lake bed deposits in the western part of the state, and in collecting and studying the vertebrate fossils found in them. These deposits occur in nearly every large valley in the westem part of the state. I have myself observed them in the valleys of the upper Missouri (above the re-rrion of Helena), Gallatin, Madison, Jefferson, Beaverhead, Ruby, Big Hole, Hell Gate, and Bitter Boot rivers, and their tributaries.