Field Report: July 5, 2019

The water in Suicide Basin has gone up by 8.25 m over the last week. On Friday afternoon, the lake level was at 436 m, which is within 1.5 to 2.0 m of the lowest point of the dam.

Dam overtopping will likely start between Saturday 6 July and Sunday 7 July. The lake may start draining subglacially before or after overtopping. In 2018, the lake started draining subglacially within ~24 hours of dam overtopping, however, the timeline may be different this season.
We suspect the 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.

On Thursday 4 July, a large calving event occurred in Suicide Basin, during which the floating ice tongue in the basin detached from Mendenhall Glacier. Rising water levels exerted forces that were strong enough to break the connection between the floating ice and the main glacier (which is not floating). During the calving event, the floating ice moved up and into the basin by several tens of meters, causing the abrupt change visible in the time-lapse image sequence.