Delineating Discontinuous Permafrost on the Seward Peninsula, Alaska, With Two-Dimensional Resistivity and Electromagnetic Techniques
Abstract
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.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2005
- Bibcode:
- 2005AGUFM.C31A1106A
- Keywords:
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- 0702 Permafrost (0475);
- 0772 Distribution;
- 1621 Cryospheric change (0776);
- 1894 Instruments and techniques: modeling;
- 5194 Instruments and techniques