DRAINAGE EVENTS FROM A GLACIER DAMMED LAKE, BEAR GLACIER, ALASKA

Among the glacier dammed lakes (GDLs) mapped by Austin Post (with L.R. Mayo) in their 1971 USGS hydrologic atlas was a small GDL on a tributary arm of Bear Glacier in south central Alaska. We investigated glacial lake outburst floods (GLOFs) originating from this GDL, which we call Ice Lake. We combine field observations and remote sensing to develop insights into the frequency and timing of drainage of Ice Lake and propagation of its outburst floods 17.5 km downstream to Bear Glacier Lake, at Bear Glacier’s terminus. We found that in recent years, Ice Lake has drained every year or two, in late summer or fall (August – October), with outbursts generally following the damming of sufficient water to create a lake area of between 0.35 and 0.5 km². Further, Ice Lake has migrated down-valley to the south since the 1990s, likely as a result of thinning of the tributary arm of Bear Glacier that dams it. We recorded (with pressure transducers) an October 2010 GLOF in which Ice Lake drained over a period of days and manifested at Bear Glacier Lake as a gradual, multi-day increase and then decrease in water levels. Glacial outburst flooding from Ice Lake creates potential hazards for sea kayakers in Bear Glacier Lake and is relevant to efforts to understand the effects of climate change on Bear Glacier.