Flood in Juneau Borough, Alaska

The two river gauges (Mendenhall Lake, Mendenhall River) on the system both reach the second highest stage in history and went above moderate flood stage. The Mendenhall Lake and River stages continue to rise for a few days when it was clear and dry. The look of the hydrograph indicated a glacier dam release but there no documented large dammed lake. After some investigating it was known that the source was from Suicide Basin 1 mile from the terminus. Near Mendenhall Lake and along the River some homes flooded, campgrounds evacuated, power cut in flooded subdivision with road cut off.

First glacier dam outburst flood on the Mendenhall Lake/River system that produced significant flood took place on July 21 2011. The source of the flood waters was from Suicide Basin and side basin on the Mendenhall Glacier, about a mile up from the glacier terminus. The Mendenhall Glacier was holding back water in Suicide Basin like a dam. The source of the flood waters was unknown for most of the event along with how much water was being impounded.