2014 MENDENHALL GLACIER JÖKULHLAUP: AN ANNUAL FLOODING EVENT FROM A JUNEAU ICEFIELD OUTLET GLACIER IN RECESSION

Suicide Basin cirque is a former ice tributary of Mendenhall Glacier. It is now an ice-covered, water-filled basin, fed by a waning icefall, glacier melt water, and waterfalls. From June 30-July 9, 2014 a transducer in the Suicide Basin Lake recorded a water level rise from 19.2-27m (63 to 88.67 feet) before dropping on July 9, 2014. This cirque basin, water level lowering, coincided with a down-glacier Mendenhall Lake level rise, as the water was discharged beneath the Mendenhall Glacier. This jökulhlaup is created when the Suicide Basin discharge water lifts the Mendenhall Glacier that has been functioning as an ice dam since the summer of 2011. An estimated 566 m³/sec (20,000 ft³/sec) was discharged from Suicide Basin yielding a total volume in the realm of 30 million m³ (11 billion gallons). Average discharge from Mendenhall Lake into the Mendenhall River in July is about 85 m³/sec (3000 ft³/sec) for the 49 years of USGS records.

A string of temperature sensors deployed from a floating buoy on Mendenhall Lake recorded temperatures every 15 minutes at depth intervals of 5 meters between the surface and -45 meters between June 7- July 18, 2014. The temperature gradient in the lake reflected the jökulhlaup release of cold water into the lake along the lake-front glacier terminus area beginning July 11, 2014 as well as a subsequent rainfall-driven flooding event from July 13-14, 2014. Data from previous summer jökulhlaups will be compared with this 2014 event.