Monitoring surficial change and forecasting subsurface thermal properties of frozen debris lobes

Abstract

Frozen debris lobes (FDLs) warrant a multi-faceted research approach due to their complexity as large scale, slow-moving, soil-based landslides located on paraglacial permafrost slopes. Since 2008, University of Alaska Fairbanks-based (UAF) researchers have been monitoring these features due to their increasing rates of downslope movement and proximity to linear infrastructure. The majority of FDLs within Alaska have been observed and/or monitored south of the Continental Divide in the south-central Brooks Range; FDL-A has been studied most extensively because of its proximity to the Dalton Highway and Trans Alaska Pipeline System (TAPS). This thesis synthesizes two research approaches: first, quantification of the detected mass movement of nine FDLs from 2011 to 2023 between discrete digital terrain model (DTM) time steps; and second, thermal modeling of FDL-A with four surface vegetation scenarios from 1970 through 2070. Change detection indicated a net volume loss of FDLs through time, while also highlighting that some FDLs advanced up to 4.1×105 m3 of material near their toes. Sediment disturbance from FDL surface runoff and accumulation also was observed from FDLs -D, -C, -A, and -7. Refined thermal modeling of FDL-A demonstrated that vegetation cover significantly drives permafrost temperature, influencing subsurface stability both now and during a warmer future. Projections indicate that if the surface cover declines, FDL-A could develop taliks and warm above -0.2 °C by 2070. The workflows presented herein provide snapshots of current FDL conditions across their surfaces (via change detection) and at depth (via thermal modeling), serving as useful tools for understanding FDL permafrost dynamics and informing mitigation strategies as FDLs continue to advance downslope.