Goldstream Valley Permafrost Map
Abstract
Airborne Electromagnetic (EM) resistivity was used together with thermal modeling to define regions of frozen and unfrozen sediments in Goldstream Valley near Fairbanks, Alaska. This study was conducted in an area of partial development with modifications to the landscape due to road construction, houses, gravel pits and drainage. Gold exploration a century ago has caused disturbance to the valley, but also contributed to subsurface data that was used by Péwé who published a permafrost map for a large portion of the Goldstream Valley in 1957. Despite the development and proximity to Fairbanks very little is known about the surficial geology and especially the thickness of sediment over bedrock. We assembled borehole data and systematically extrapolated these data over the valley to recreate the layered structure of silt, gravel and bedrock that can be expected in this valley, which was never glaciated. The layered surficial geology was then used with the resistivity calculated from the airborne EM survey to find likely boundaries between frozen and unfrozen sediment. The valley was first mapped based on resistivity values, which was verified using borehole data and LiDAR elevation data for areas of ice wedge degradation. It was found that thawing permafrost has a resistivity very close to unfrozen sediments and determining the exact boundary is difficult. One of the problems is that fine grained sediments, at below freezing temperature have liquid water that can support electric currents and small scale variability of temperature and ice content cause those currents to flow around resistive bodies such as massive ice. Combining our map with thermal modeling provided further insights into the structure of permafrost distribution. However the complexity of ground ice distribution, fire extent and severity, beaver activity and human construction are all temporal changes in the surface conditions that is hard to simulate. Further analysis with higher resolution remote sensing devices may provide further insights into the presence of ground ice and the potential future collapse of the surface with infrastructure and houses that are built on permafrost in Goldstream Valley.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.C13E1392D
- Keywords:
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- 0702 Permafrost;
- CRYOSPHERE;
- 0708 Thermokarst;
- CRYOSPHERE;
- 0768 Thermal regime;
- CRYOSPHERE;
- 0774 Dynamics;
- CRYOSPHERE