Exploring Subsurface Temperature Dynamics of Frozen Debris Lobes through Thermal Modeling

Abstract

Within the Brooks Range of Alaska are slow-moving permafrost-landslide features known as frozen debris lobes (FDLs). These features were originally identified during the construction of the Trans Alaska Pipeline System and the Dalton Highway in the 1970s, at which time they were thought to be inactive. In 2008, members of our research team recognized that FDLs are indeed actively moving, spurring on a long-term monitoring and field investigation program. Over the last decade, we have increased our understanding of FDLs through drilling, sampling, analyzing ground temperatures and strain rates obtained via subsurface instrumentation, measuring surface movement, and analyzing long-term and seasonal movement rates using historic imagery, light detection and ranging (LiDAR), and interferometric synthetic aperture radar (InSAR) data. Our research indicates that FDL movement is sensitive to temperature and water pressure, which is expressed in seasonal fluctuations of movement rates. In an effort to learn more about FDL temperature dynamics, here we explore the interaction between subsurface temperature and FDL vegetation coverage using two-dimensional, finite element thermal modeling. Model results indicate that when a section of an FDL is simulated to have an exposed mineral surface, a through-talik forms within the permafrost after 50 years. As more of the FDL surface is disturbed by movement and transitions to a bare, mineral surface, the size of the talik increases. When the entire surface is bare mineral soil, permafrost conditions are no longer sustainable beneath the FDL. We present comparisons of model results to observed field conditions, and predict surface destabilization for FDL-A.