Forecasters expect the glacial lake responsible for producing Juneau’s annual glacial outburst flood to be full this week.
The National Weather Service predicts that Suicide Basin will fill to the top on Tuesday, Aug. 11 or Wednesday, Aug. 12. That’s a bit later than the initial estimate since cool, dry weather fills the basin more slowly than warm and rainy weather.
The flood typically begins within a week after the basin is full, but it can happen at any time.
The glacial outburst flood starts when the water pressure in Suicide Basin builds up so much that it bores through the ice and floats Mendenhall Glacier, releasing billions of gallons of water into the suburban valley below.
Last year, the Weather Service issued an alert that the basin was full and spilling over the glacier on Aug. 10. Then the record-breaking flood crested on Aug. 13.
When the flood begins, the Weather Service will forecast the size of the flood and when it will peak. After scientists have about a day’s worth of data showing how quickly the water is moving, they might adjust that forecast.
In past years, the flood crested roughly 48 hours after it began.
The City and Borough of Juneau encourages Mendenhall Valley residents in the flood zone to evacuate when Suicide Basin begins to release.
