The Impacts of Rapid Climate Change on Mass Movements in Denali National Park, Alaska

The eastern portion of Denali National Park and Preserve (DENA) is a high-altitude (800 m - 1400 m asl) alpine (63°N) environment that is experiencing a new wave of geomorphological destabilization as a result of a warming climate. Hillslopes are becoming unstable as permafrost (perennially frozen ground) thaws, which can then trigger various types of mass movements. Mass movements have the potential to affect the structural integrity of the Denali Park Road, alter the flow of groundwater or river systems, uproot vegetation, and negatively impact the safety of the half a million visitors that the park receives every year. The purpose of this study to understand how mass movements in DENA are affected by different aspects of climate change, such as increased rainfall and rising air and ground temperatures, to determine when and why DENA's landscape experienced periods of instability in the past, and to better understand the potential trajectory of current landscape changes. To establish a timeline of mass movement activity since the early Holocene, we performed lichenometry on relict rockfalls and rock glaciers to determine when the paleo-landscape began to stabilize. Many of the ongoing mass movements in DENA are reactivations of older landslides or rock glaciers that were active in the early Holocene, such as the Mile 35 Slide. The Mile 35 Slide is a polygenetic mass movement that initiated along the Park Road during the summer of 2016. We used a combination of remote sensing, field surveys, and local weather records to establish a four-year timeline of this landslide's movement and how it responded to rapid changes in climate. Observations of the Mile 35 Slide illustrate the important role played by freeze/thaw processes and extreme rainfall events in DENA mass movement initiation and progression. Our lichenometric analysis of rockfalls in DENA reveal earlier episodes of widespread mass movement, the oldest dating to ca. 11,000 yr. BP. This indicates that DENA has experienced several previous episodes of landscape instability in the past, and that cycles of stability/instability are characteristic of this environment. We conclude that ongoing mass movements are occurring on hillslopes that were unstable in the past and that rapid changes in climate are important triggers of mass movements in this alpine environment.