Glacial Geophysics
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| Multi-channel Multi-offset GPR on Bench Glacier |
Bench Glacier, Alaska (2003, 2005, 2006)
Pika Glacier, Denali Park, Alaska (2001)
Galena Creek Rock Glacier, Wyoming (2000)
Bench Glacier
Project Summary
As the present climate warms, meltwarer hydrology and water's influence on glacier motion will be an increasingly important aspect of thermal and dynamical processes of Greenland and other large ice masses. With influence on sea level, ocean circulation, and the general climate system, the sliiding stability of Greenland and other ice sheets has strong bearing on globally important processes and this warrants full understanding. Unfortunately, in situ investigations of the mechanical linkages between water input and enhanced motion are difficult, if not impossible, on the vast and thick ice sheets. This problem motivates interest in the hydrology and dynamics of smaller mountain glaciers, where the manageable scale can be utilized to investigate key glaciological processes with the goal of up-scaling.
We cannot expect to ever fully understand basal motion without advancing our knowledge of the hydrological processes in operation within and beneath glaciers. Understanding of these processes will greatly aid our abilitiy to interpret time/space variability in glaicer motion, and ultimately, our ability to predict future changes to glaciers or reconstruct climate history under given glacial scenarios. With these goals in mind, this project focuses on advancing our knowledge of a critical link between hydrological processes and basal sliding: mechanisms of englacial water storage and routing of surface water to the bed.
Location of Bench Glacier
Topographic map of Bench Glacier
Satellite image of Bench Glacier area
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| Multi-channel Multi-offset GPR on Bench Glacier |
2006 Summer Field Season
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| Trace positions for 5m offset 3D grid survey |
- 3D GPR survey of 100 m square grid
- 200 m grid time lapse GPR survey
- 2D Axial profile along center of glacier
- 2D cross sections along length of profile Borehole VPR in 100 m grid
- Snow tomography
Results
Pika Glacier
Project Summary
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Instrumentation and
methods for measuring snow properties
are compared in an investigation of meter-scale variability of snow
characteristics at Pika Glacier, Alaska Range, central Alaska. Field
measurements were
conducted within a
20x20x2 meter plot in an area with no slope or topography along the
glacier
centerline. Snow
within the plot was
characterized by 600+ measurements of snow density, 400+ measurements
of snow
temperature, stratigraphic mapping in 19 snow-pits, and with a pulse
radar
system along 20 profiles. Density
was
measured manually by weighing methods, and was calculated from electric
permittivity measured using both a hand permittivity probe and radar
velocity
analysis.
Manual measurements of density and stratigraphic mapping in
snow-pits suggest a relatively homogeneous snowpack, yet image analysis
of a
back lighted snow column reveals extremely complex stratigraphy. Both
the permittivity
probe measurements and
the radar profiles are effective at revealing the stratigraphy at an
intermediate
scale. Additionally,
independent density
calculations from the two methods are in good agreement with each other
and
with the manual measurements.
The
reach shows
strong spatial correlation of density and
temperature at meter scale. Contrasting
high and low density layers extend across the entire study area, and
the
temperature profile is similar at all locations.
Conclusions
Both the permittivity probe measurements and the radar profiles are effective at revealing the stratigraphy at the scale of cm. Independent density calculations from the permittivity probe and inversion of radar data are in good agreement with each other and with the manual measurements. The stratigraphy showed complex fine scale variations; identifiable layers extended mm in the vertical and 1-10 cm in the horizontal directions. Large contrasts in the density and temperature profiles were laterally continuous over 10s of m. The level of complexity identified within the stratigraphy is dependent upon the measurement tool used. Visual mapping of a snow pit wall identifies a very low level of the actual stratigraphy present.
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Figure A |
Figure B |
Figure C |
Galena Creek Rock Glacier
Project Summary
A 2D GPR survey was performed on the Galena Creek rock glacier in order to verify that modern high frequency radar can image the ice thickness of ice in a high altitude rock glacier environment. Previous attempts to image rock glaciers with radar have proved unsuccesssful. In these test the data collected resolved the glacier bed as well as an interglacial layer (see figure below).
Results
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| Axial profile along the rock glacier using a 50 MHz ground penetrating radar antenna. |
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| Multi-channel Multi-offset GPR on Bench Glacier |
Check out the University of Wyoming webpage for more results on the Galena Creek work.