Characterizing a Frozen Debris Lobe, Dalton Highway, Alaska

Frozen debris lobes (FDLs) are slow-moving landslides along permafrost-affected slopes. Within the Dalton Highway corridor in the southern Brooks Range, Alaska, we have identified 43 FDLs, with 23 occurring less than one mile uphill of the Dalton Highway. FDL-A, which is the largest and closest FDL to the Dalton Highway, was just over 42 m away from the highway embankment when measured in August 2014. Since the completion of a preliminary subsurface investigation in 2012, we continue to collect subsurface temperature and inclinometer data, to measure surface movement rates, and to make field observations, which reveal the dynamic nature of FDLs. Significant rainfall during the summer of 2014 caused a deepening of the active layer on FDL-A and exposed massive “infiltration” ice in the head scarps of two retrogressive thaw slumps on its surface. The infiltration ice occurs in bands associated with transverse and longitudinal cracks, and the 2014 observations indicate that FDL-A may contain more massive ice than previously indicated. FDL-A moves mostly through basal shearing and through slow to moderate flow, which is highly dependent on temperature. The average rate of movement of FDL-A from 2013 to 2014 was 1.3 cm day⁻¹. Comparing this value to the trend of historic rates indicates that the overall rate of movement of FDL-A continues to increase.