HR: 0800h
AN: C31A-1106    [Abstracts]
TI: Delineating Discontinuous Permafrost on the Seward Peninsula, Alaska, With Two-Dimensional Resistivity and Electromagnetic Techniques
AU: * Astley, B N
EM: Beth.N.Astley@usace.army.mil
AF: Cold Regions Research and Engineering Laboratory, Bldg 724, Fort Richardson, AK 99505 United States
AU: Delaney, A J
EM: Allan.J.Delaney@usace.army.mil
AF: Cold Regions Research and Engineering Laboratory, Bldg 4070, Fort Wainwright, AK 99703 United States
AU: Douglas, T A
EM: Thomas.A.Douglas@usace.army.mil
AF: Cold Regions Research and Engineering Laboratory, Bldg 4070, Fort Wainwright, AK 99703 United States
AU: Engel, C
EM: Chandler.Engel@uvm.edu
AF: University of Vermont, College of Engineering and Mathematics 213 Votey Bldg, Burlington, VT 05405 United States
AB: Soils at the Stewart River Training Area near Nome, Alaska were investigated in July 2005 to determine suitability for trail relocation. The area contains classic cryogenic features including thermokarst ponds, ice wedge polygons, sorted circles, cobble pavement, and solifluction lobes. The soils range from silty gravel to clayey silt, typical of a glacial depositional environment. Discontinuous permafrost is present in the region. We collected 2D resistivity and EM31 on a study grid 525 m long by 300 m wide that was bisected north to south by a stream valley. We used Wenner, Schlumberger, and Dipole-Dipole arrays with a 5-m electrode spacing and array length of 275 m. Soil pits were excavated to determine the depth to the top of permafrost, to measure soil horizon thicknesses and to collect soil samples for water content measurements. Frost probes were also used to determine permafrost depth. Soil moisture content ranged from 47% by weight in frozen silt to 11% in thawed poorly-sorted silty gravel. The depth to permafrost ranged from 15 to120 cm below the surface. Soil type appeared to be the dominant control on the presence of permafrost in the study area with all permafrost found in silt and no permafrost found in gravels. The presence of willow thickets corresponded with thawed areas. Willows were absent in areas containing massive permafrost, but were present in low numbers where permafrost was degrading. High resistivity anomalies correlated with frozen soil on the east side of the stream. On the west side of the stream, high resistivity associated with a cobble pavement and large gravel clasts had similar resistivity values as permafrost. The EM31 data correlated well with permafrost, and determined the location of a highly conductive area in the schistose bedrock. Our results suggest that a combination of geophysical tools and shallow ground truth explorations using probes and shovels can provide an accurate delineation of horizontal and vertical permafrost extent.
DE: 0702 Permafrost (0475)
DE: 0772 Distribution
DE: 1621 Cryospheric change (0776)
DE: 1894 Instruments and techniques: modeling
DE: 5194 Instruments and techniques
SC: Cryosphere [C]
MN: Fall Meeting 2005