[A-CG46] Science in the Arctic Region

[ACG46-13] Spatial heterogeneous permafrost thaw subsidence around Beaver Creek, Yukon, Canada, detected by ALOS-2 InSAR and onsite observation

*Kazuki Yanagiya¹, Masato Furuya², Go Iwahana³, Antoine Séjourné⁴ (1.Japan Aerospace Exploration Agency, 2.Department of Earth and Planetary Sciences Hokkaido University, 3.International Arctic Research Center, University of Alaska Fairbanks, 4.Geosciences Paris-Saclay, University of Paris-Saclay)

Keywords:Permafrost, Wildfire, Thermokarst, SAR, InSAR, ALOS-2

Permafrost thawing will accelerate the decomposition of soil organic carbon, and it is concerned as positive feedback to global warming. The international research project "Permafrost degradation impacts on soils, human societies, water resources and carbon cycle (PRISMARCTYC)" conducted the first field observation around Beaver Creek (BC), Yukon, Canada, in August 2022 to investigate the relationship between active/receding thermokarst lake, wildfires, and permafrost degradation. The boundary of McConnell glacier in the Late Pleistocene is located south of BC. Previous studies reported that the yedoma layer has developed in the sedimentary layers, which had formed in depressions between the moraine deposit around BC.

In addition, we detected the fire signals in 2019 and 2022 near BC by Sentinel-2 and NASA FIRMS optical images. The 2019 fire scar is located 15 km southeast of BC, inside the extent of past McConnell Glacier. The fire burned 26 km² on 6-11th July 2019 and 2.5 km² on 8-13th September 2019. In general, the loss of the surficial vegetation layer as a heat insulator at the fire scar causes deep and rapid permafrost thawing for several years to a decade after the fire.

Here, we present Interferometric Synthetic Aperture Radar (InSAR) and onsite thaw depth observations near BC. We analyzed JAXA's ALOS-2 L-band SAR satellite data to detect annual and interannual ground subsidence due to permafrost thawing, especially inside the fire scars. The thaw depth data was manually measured with a metal probe with an accuracy of cm in August 2022.

InSAR image from July 2019 to July 2020 showed a loss of coherence due to vegetation loss by fire. Coherence loss and unwrapping errors are also dominant in the annual InSAR image from July 2020. The one-year interferogram from July 2021 was coherent and detected spatially heterogeneous subsidence signals inside the 2019 fire scar. The InSAR image showed a subsidence signal at most 10 cm in the Line of sight (LOS) direction in the southern part of the 2019 scar. The thaw depth of the most subsided areas is 20-30 cm deeper than the unburned control site. Also, we made a transect on the slope in the northern part of the 2019 scar to validate the subsidence amount with thaw depth data. About 7 cm subsidence signals in the LOS direction were detected from 2021 to 2022 in the middle of the slope. The subsidence signal was not detected in the gravel-rich areas in the upper and lower part of the slope. The Spatial heterogeneity of the subsidence signal can correspond to the distribution of moraine deposits around BC. We will conduct a second onsite observation in 2023 and further collaborate with other researchers on the GNSS, thermokarst lake, and permafrost core surveys.