Observation of a rapid lake-drainage event in the Arctic: Set-up and trigger mechanisms, outburst flood behaviour, and broader fluvial impacts

Lakes set in arctic permafrost landscapes can be susceptible to rapid drainage and downstream flood generation. Of many thousands of lakes in northern Alaska, hundreds have been identified as having high drainage potential directly to river systems and 18 such drainage events have been documented since 1955. In 2018 we began monitoring a large lake with high drainage potential as part of a long-term hydrological observation network designed to evaluate impacts of land use and climate change. In early June 2022, surface water was observed flowing over a 30-m wide bluff, with active headward erosion of ice-rich permafrost soils apparent by late June. This overflow point breached rapidly in early July, draining almost the entire lake within 12 h and generating a 191 m(3)/s flood to a downstream creek. Water level and turbidity sensors and time-lapse cameras captured this rapid lake-drainage event at high resolution. A wind-driven surface seiche and warming waters following ice-out helped trigger the initial thermomechanical breach. We estimate at least 600 MT of lake sediment was eroded, mobilized, and transported downstream. A flood wave peaking at 42 m(3)/s arrived 14 h after the initial breach at a river gauge 9-km downstream. Comparing this event with three other quantified arctic lake-drainage floods suggests that lake surface area coupled with drainage gradient height can predict outburst flood magnitude. Using this relationship we estimated future flood hazards from the 146 lakes in the Arctic Coastal Plain of northern Alaska (ACP) with high drainage potential, of which 20% are expected to generate outburst floods exceeding 100 m(3)/s to downstream rivers. This fortunate and detailed drainage-event observation adds to a growing body of research on the impact of lakes on arctic hydrology, hazard forecasting in a region with an increasing human footprint, and broader processes of landscape evolution in arctic lowlands.