C012-0011
Patterns and rates of soil movement and shallow failures across several small watersheds on the Seward Peninsula, Alaska.

Tuesday, 8 December 2020
Poster
Joel C Rowland, Los Alamos National Laboratory, Earth and Environmental Sciences, Los Alamos, NM, United States, Joanmarie Del Vecchio, Los Alamos National Laboratory, Los Alamos, NM, United States, Rachel Glade, University of Pennsylvania, Philadelphia, PA, United States, Michael Fratkin, Los Alamos National Laboratory, Earth & Environmental Sciences, Los Alamos, United States, Emma Lathrop, Los Alamos National Laboratory, Earth and Environmental Science Division, Los Alamos, NM, United States and Simon Zwieback, University of Guelph, Guelph, ON, Canada
Abstract:
Across a shrubby, tussock tundra, permafrost-dominated landscape we have documented a broad range of soil movement processes ranging from solifluction and steady creep to rapid shallow landslides and gully development of hollows. Using differential GPS (DGPS) surveys, UAS acquired imagery and elevation data, soil sampling, radio carbon dating of soils, and satellite based Interferometric Synthetic Aperture Radar (InSAR) analysis we have quantified rates and patterns of soil movement. Repeat survey of fixed ground targets with DGPS show rates of soil movement of a few to 10 centimeters per year. Highest rates of soil movement generally lie upslope of broad rumbled arcuate fronts of apparent earth flows 5 to 10 meters in width. Also associated with these regions of high displacement rates are extensive regions of shallow failures marked by bare soil exposures due to tears in the thick tundra vegetation mat. While prevalent across the watershed prior to 2019, a number of new failures appeared to have been associated with heavy rainfall and saturated soil conditions in August of 2019. Using UAS acquired imagery, we have mapped the occurrence of these failures in images from both 2018 and 2019 and we are exploring potential associations with hillslope position, aspect, slope, and contributing drainage area. The single largest displacement of soils in 2019 occurred along the axis of valley hollow experiencing active gullying. An InSAR analysis of this region of the Seward Peninsula shows ground surface displacement consistent with our field-based measurements. The InSAR results suggest that our study site is one of the more active areas of soil displacement in the southwestern region of the Seward Peninsula but it is not unique. Our observations suggest that background rates of soil movement on these permafrost hillslopes is relatively rapid and that episodic events, such as landslides, can dramatically disrupt vegetation cover and promote rapid erosion of the underlying soils. Additionally, though apparently common, rapid soil movements and landslides are not readily detectable without on the ground surveys or very high-resolution (< 0.25 m) imagery, making wide spread documentation and attribution of these failures extremely challenging.
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