Internal Structure, Kinematics, and Prehistory of Frozen Debris Lobe‐A (FDL‐A), Brooks Range, Alaska

Frozen Debris Lobe‐A (FDL‐A)—one of hundreds of FDLs in the Brooks Range of northern Alaska—is a slow‐moving landslide in permafrost that has been the subject of research since 2008 due to its close proximity to the Dalton Highway. Here, we synthesize more than a decade's worth of climate and surface measurements of monitored FDLs, and the results of subsurface exploration of FDL‐A (including electrical resistivity tomography surveys and subsurface measurements of temperature, groundwater pressure, and horizontal displacement), to describe FDL‐A's internal characteristics and kinematics as it travels downslope and entrains organic material. Long‐term measurements indicate an increased rate of movement in the monitored FDLs, which correlates to both years of late snowfall and years of greater‐than‐average snow depth. FDL‐A maintains a “baseline” shear rate throughout the year (currently ~2 cm day −1 ), as well as an annual movement cycle with a spring rate increase associated with snow melt and a maximum movement rate when the active layer is the deepest in October/November. The active layer serves as a “conveyor belt,” transporting the near‐surface soils and vegetation to the toe, where FDL‐A's basal shearing overrides them; we hypothesize that the incorporated organic content facilitates movement in the shear zone by increasing the soil's unfrozen water content. Using a collection of radiocarbon ages sampled from throughout FDL‐A, we present a possible history of its downslope journey, connecting pulses of movement to periods of increased air temperature during the Holocene. This interpretation of FDL‐A's kinematics will aid in developing geomechanical models to predict FDL‐A's downslope trajectory, with the ultimate goal of informing mitigation solutions for the adjacent infrastructure.