Ice-marginal Lake Evolution in Alaska (1970 to 2019) and Associated Glacial Lake Outburst Flood (GLOF) Hazard

Abstract:

Glacial lake outburst floods (GLOFs) occur when a lake dam (ice, landslide, bedrock, or moraine) suddenly fails or is breached, catastrophically releasing a large volume of water. GLOFs can have massive impacts on downstream river channel morphology, disrupt ecosystem equilibrium, and destroy infrastructure, whether that be from the flood itself, increased sediment fluxes, or a change in the glacial drainage system. Glacial lake inventories are a critical first step to assess GLOF potential, and inventory time series provide insight into the temporal evolution of lakes. Previous studies suggest that present-day global deglaciation will increase the number and extent of ice-marginal lakes, however, this hypothesis has not been tested in Alaska with a detailed spatiotemporal study. This study quantifies ice-marginal lake (>0.05 km²) occurrences, area, and location in four subregions of Alaska at 5-year intervals over the past 50 years using historical airborne imagery (1970) and Landsat imagery (1984-2019) compiled in Google Earth Engine. In all four subregions, the total area of ice-dammed lakes decreased over time, while the area of moraine-dammed lakes increased. The Eastern Alaska Range recorded an 164% increase in total lake area between the years 1984 (3.4 km², n=13) and 2019 (8.9 km², n=22), with an increasing trend in median lake area. The Western Alaska Range recorded an 104% increase in total lake area from 1984 (98.7 km², n=28) to 2019 (201.6 km², n=53), but with a decreasing trend in median lake area due to the formation of new, smaller lakes commonly on debris-covered glacier tongues. Trends in cumulative area and occurrence differ between ice-dammed and moraine-dammed lakes, highlighting the important role of dam type and location when considering lake evolution. This dataset reveals critical information about how and why glacial lakes in Alaska have changed historically and provides a baseline to predict future lake evolution and GLOF hazards in Alaska.