Seasonal Solifluction Processes in Warm Permafrost Arctic Landscape Across Adjacent Hillslopes

The Science

Understanding controls on soil movements along hillslopes is crucial to improving the assessment and prediction of carbon fluxes and infrastructure hazards in the warming Arctic. A team of researchers established a novel sensor network to monitor soil temperature and deformation at 48 locations spanning adjacent hillslopes in a warm permafrost environment. Data reveals that during the thawing season, movements predominantly occur near the thawing front, commencing as thawing reaches depths ranging from 0.4 to 0.75 meters. Key parameters governing shallow soil movement processes include slope angle and soil thermal state.

The Impact

This study underlines the importance of accurately estimating subsurface thermal state for assessing and predicting slope instabilities. Furthermore, this study contributes to a deeper understanding of the intricate mechanisms impacting soil carbon fluxes as the Arctic permafrost thaws and the seasonal thawing dynamic changes.

Summary

Solifluction processes in the Arctic are highly complex, introducing uncertainties in estimating current and future soil carbon storage and fluxes and assessing hillslope and infrastructure stability. This study aims to enhance understanding of triggers and drivers of soil movement along permafrost-affected hillslopes in the Arctic. To achieve this, researchers established an extensive soil deformation and temperature sensor network, covering 48 locations across multiple hillslopes within a 1 km² watershed on the Alaskan Seward Peninsula.

Depth-resolved measurements down to 1.8 m depth have been reported for May to September 2022, a period conducive to soil movement due to deepening thaw layers and frequent rain events. Over this period, researchers showed that movements occur close to the thawing front and are initiated as thawing reaches depths of 0.4 to 0.75 m. The largest movements were observed at the top of the southeast-facing slope, where soil temperatures are cold and slopes are steep.

Three primary factors influenced movements: slope angle, soil thermal conditions, and thaw depth. These factors affect soil properties, which are crucial determinants of slope stability. This underscores the significance of a precise understanding of subsurface thermal conditions, including spatial and temporal variability in soil temperature and thaw depth, when assessing susceptibility of slope instabilities. This study offers novel insights into patterns and triggers of Arctic hillslope movements and provides a venue to evaluate their impact on soil redistribution.

Principal Investigator

Sylvain Fiolleau
Lawrence Berkeley National Laboratory
[email protected]

Co-Principal Investigator

Baptiste Dafflon
Lawrence Berkeley National Laboratory
[email protected]

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
[email protected]

Funding

This research was supported by the Biological and Environmental Research program within the U.S. Department of Energy’s Office of Science as part of the Next-Generation Ecosystem Experiments Arctic (NGEE Arctic) project.

References