Field Report: July 12,2018

  • Water level at 5:50 pm: ~438.5 m
  • Water level increase 3:30 pm–5:50 pm: 9 cm (equivalent to 0.93 m/day)
  • Lowest point of dam: ~441.5 m

As of last night, there was a 3 m difference between the water level elevation and the elevation of the lowest point of the dam. At the current rate of water level increase, the lake would start spilling over between Sunday evening and Monday morning. While the water level increase slowed down last night (cold, no rain), warm temperatures today and rain on Saturday/Sunday may reverse this trend again.

If the lake spills over, the water starts flowing along the glacier boundary. The water may then start incising the ice, which in turn will increase the water flow and thus the rate of ice incision (positive feedback). It is unlikely that the water will be flowing along the glacier boundary over an extended distance. Instead, we would expect it to find its way into the glacier at one of the depressions visible in digital elevation models (depressions in elevation models are typically crevasses or moulin-type holes). Predicting the timeline of this process is challenging, especially because we have not observed it at Suicide Basin previously. However, we would suspect this process to unfold more slowly than a drainage event via subglacial conduit.

Note that although the lake is close to spilling over, draining via subglacial conduit may still occur instead (a combination of processes may occur as well). In some of our preliminary flood prediction runs covering this scenario, peak levels at Mendenhall Lake reach 12 feet, however, actual peak levels will depend heavily on the Mendenhall baseflow during the event and the rate at which Suicide Basin will be draining. The latter can vary from event to event and is thus difficult to predict. Better predictions will be possible once the event has begun.

Current volume estimates are very similar to the volumes of the 2016 event, i.e., around 0.035 km3. Note that such estimates come with an uncertainty of at least 10%.