Field Report: July 8, 2019

The lake started overtopping the dam on Sunday 7 July in the morning and reached its maximum level shortly thereafter. The water level in the basin has been slowly dropping since due to erosion of the overflowing water at the ice dam. Subglacial drainage has not begun as of Monday afternoon. In 2018, the lake started draining subglacially within ~24 hours of dam overtopping. The timeline will be different this season, however, accurate predictions are not possible. We suspect subglacial drainage will happen within the next few days.

The overflowing water runs along the glacier boundary down to the ice bench next to Temsco’s camp. Along the way, some or all of the water disappears in moulins/crevasses just to reappear further downglacier. Downglacier of Temsco’s camp, the water pools and disappears into the glacier for good.

We suspect the remaining water volume in the basin to be slightly lower than last year. Note that the peak flow at Mendenhall River will depend not only on the total water volume in Suicide Basin. It will also be controlled by the drainage characteristics (i.e., how fast and how complete) and by the Mendenhall River baseflow during the event.