A Dendro-Geomorphological Analysis of the Slate Creek Landslide, Alaska

Mass movements are some of the main ways that hillslopes re-equilibrate to a new climatic regime. The impacts of climate change on mass movements are predicted to be especially pronounced at high latitudes where temperatures are warming most rapidly, and precipitation is increasing at higher rates than at lower latitudes. Because of its instability once thawing occurs, the presence of perennially frozen ground (permafrost) further increases the probability that mass movements will increase significantly in high latitude landscapes over the next few decades. With these predictions in mind, it is likely that critical infrastructure in Interior Alaska will be increasingly threatened by mass movements over the next few decades. We sought to understand the dynamics of the Slate Creek Landslide that is currently encroaching on the Parks Highway at Mile 258 along the northern front of the Alaska Range. To accomplish this, we use the dendrochronology of leaning and split trees growing on the landslide surface, time series of landslide movement based on repeat aerial photography and LIDAR imagery, and differential GPS measurements of landslide movement at monthly to biennial time scales. Results show that different parts of this landslide have moved at and continue to move at rates ranging from 0.2cm up to 7m/year. Repeat LiDAR imagery also suggests that the head-scarp of the landslide has retreated 50 m since 2011. Based on these data and the number of tree samples (n=122), the mid-1970s to early 1980s was a period of enhanced landslide movement. We tentatively correlate the increased movement of the Slate Creek Landslide with the increase in precipitation and abrupt shift to warmer air temperatures that accompanied the regime shift in the Pacific Decadal Oscillation in the mid-1970s.