NSF-SNSF: HOOLGOYH: Deciphering long-term effects of thawing on permafrost instability in the Brooks Range, Alaska

University Of Alaska Fairbanks Campus, Fairbanks AK

Investigators

Abstract

Amplified warming in the Arctic may be triggering a surge of mass movements. In the Brooks Range of northern Alaska, slow-moving, frozen landslides (Frozen Debris Lobes; FDLs) are becoming noticeably more active, and they now threaten critical infrastructure like the Trans Alaska Pipeline and Dalton Highway. Unlike other sectors of the cryosphere (glaciers, sea ice), little is known about how responsive frozen mass movements have been to past episodes of climate warming and cooling. For instance, it is unknown when today’s period of enhanced mass movement began in the southern Brooks Range, what climatic conditions triggered it, and how unusual it is compared to the last several centuries. Moreover, a lack of knowledge about how topography and land cover influence the climate sensitivity of frozen mass movements has prevented researchers from predicting where and when new mass movements may emerge in our warmer future. The main aim of this project is to use geomorphic monitoring, remote sensing, and the growth records of trees growing atop FDLs to determine the seasonality and interannual variability of FDL instability over the last ~300 yrs. By comparing reconstructed FDL instability with remote sensing and climate records, researchers will use the past climate sensitivity of these natural hazards to assess the future risk they pose as Arctic warming accelerates. This project will focus on actively moving FDLs in the Central Brooks Range, some of which encroach upon the Dalton Highway and the Trans Alaska Pipeline System corridor. Preliminary tree-ring data indicate that episodes of ground instability associated with FDL movement are recorded in the annual records of the old-growth white spruce trees growing on the FDLs. For the long-term reconstruction of FDL dynamics, researchers will use dendrogeomorphic techniques on 15 FDLs to generate annually resolved records of multi-centennial FDL instability. To monitor sub-seasonal ground movement and tree-growth variability, dendrometers, tiltmeters, and on-site climate records will be used at one FDL location. Quantitative wood anatomy will also be used to detail the seasonality of past movement episodes. Remote sensing will be employed to assess interannual rates of movement in ~160 FDLs in the region since 1955. Daily historical and gridded monthly climate data as well as topo-geomorphic parameters will be fed into a Hierarchical Bayesian Modeling Framework to aggregate site reconstructions and to derive regional trends/drivers of FDL behavior. This project will test three hypotheses: (i) FDL instability is sensitive to changes in air temperature and precipitation, including snow accumulation and heavy summer rainstorms; (ii) the extent/rate of FDL instability was first enhanced during post-Little Ice Age warming; (iii) recent instability is unprecedented both in extent and rate over the past 300 yrs. As FDL activity is thought to be a harbinger of more widespread slope instability in the Arctic, these results will help answer the fundamental question of how Arctic landscapes respond to ongoing change. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.