Time Series Analyses of Interior Alaska Thermokarst Using Airborne and Terrestrial Lidar

Permafrost in Interior Alaska, with a mean annual temperature of -1C, is ecosystem protected by thick organic mats, moss, and high moisture content vegetation and soils. Projections indicate increasingly warm high-latitude conditions with a greater fraction of liquid to solid precipitation. Recently, consecutive years of above-average summer precipitation has led to substantial changes in ice-rich Interior Alaska boreal permafrost landscapes. Both upland and lowland landscapes are exhibiting rapid changes in surface characteristics. Thermokarst pits, gullies, and collapse features have expanded, stream silt loads have increased, and undercut and tilted Picea mariana trees are common. A time series of aerial and terrestrial lidar measurements have been collected on interior upland and lowland Alaska research sites from 2014 to 2018. These years include the highest (2014) and third highest (2016) summer precipitation totals in Fairbanks' 91-year record. Our survey dataset, aggregated and corrected, allows us to identify and calculate changes in surface elevation and identify where and when landscape changes occurred. Coincidentally, a rich dataset of high-resolution optical imagery allows us to examine relationships among lidar-detected surface changes and imagery. In uplands, surface subsidence and increased inundation are apparent in localized areas such as streams and lakes. In some places, subsidence and elevation loss is on the order of meters over a few years. Other areas on the landscape show increased elevations from silt deposition and lingering aufeis. Lowland subsidence is primarily adjacent to stream and bog edges, but is most pronounced and expansive on lake margins. Our goal is to identify, and eventually predict, permafrost landscape changes due to projected increases in summer precipitation.