Quantifying Volumetric Change Detection of Nine Frozen Debris Lobes in the South-Central Brooks Range, Alaska

ABSTRACT Frozen debris lobes (FDLs) are slow-moving landslides in permafrost located throughout the Brooks Range, Alaska. Here, we present the first regional-scale, multi-FDL change detection analysis using light detection and ranging (LiDAR) datasets collected along the Dalton Highway and Trans Alaska Pipeline System corridor. We used digital terrain models of difference across four time intervals (2011, 2015, 2020, and 2023) to quantify surface deformation and volumetric change for nine FDLs. Our workflow included field-based verification of results (necessary given the slow-moving nature and indistinct boundaries of FDLs). We developed a minimum level of detection for mass movement, mapped statistically significant change, and quantified this change over a decadal timescale. Results indicate that FDLs exhibit a net volume loss over time; however, individual FDLs mobilized up to 4.7 × 104 m3/yr, averaged over a 5-year period. In addition to dynamic mass movement, FDLs pose other hazards, including increasing encroachment on valley floors and disruptive sediment transport. Quantifying FDL volume change provides constraints on sediment flux and deformation rates, which aids in designing and evaluating engineering alternatives to mitigate impacts to linear infrastructure. At present, FDLs have affected downslope infrastructure, requiring the 2018 reroute of the Dalton Highway and blocking culverts with sediment. We recommend annual monitoring to track distinct changes in FDL geometry and deposition zones, quantify volume transport, and characterize the stability of FDLs as they advance downslope.