Wednesday, December 15, 2021
A glacial lake outburst flood from Suicide Basin is pushing Juneau's Mendenhall River toward a forecast crest near 16.6 feet in major flood stage, forcing evacuations as Alaska declares a disaster.
A glacial lake outburst flood is pushing the Mendenhall River toward major flood stage in Juneau, Alaska. Water began draining from Suicide Basin, a side pocket of the Mendenhall Glacier, on August 11, and the river rose through minor flood stage overnight. The National Weather Service expects a crest between 16.1 and 16.6 feet on the morning of August 13, just under the 16.65 foot record set on this same date in 2025. Those numbers are a forecast, not a final reading, and the river is still rising.
What makes this hazard unusual is the way it starts. Meltwater and rain collect behind the glacier in Suicide Basin until the pressure lifts or breaches the ice, and the basin empties in a rush that has nothing to do with the weather that day. Juneau now sees a release almost every summer, and each one has run higher as the glacier thins. The City and Borough of Juneau advised residents in the marked evacuation zones to leave, named evacuation routes toward Auke Bay and Egan Drive, and opened a Red Cross shelter at the Floyd Dryden Gymnasium. The state issued a disaster declaration to speed assistance and mitigation work. The Weather Service, USGS, the Army Corps of Engineers, and the Tongass National Forest are tracking the basin and the river together.
Glacier country is not the only place this matters. Any household near a river learns what a flood teaches everywhere, which is that water rises faster than people expect and a foot of it can move a car. Knowing whether you sit on a floodplain and where your high ground lies is basic flood readiness, and homes on low ground can blunt the first surge with sandbags set before the crest rather than during it.
Once water is in the streets, the rules are simple and worth setting in advance. Do not drive or walk through moving water, move what you can to higher ground, and keep drinking water aside, because a boil water notice often follows once a system takes on floodwater. Where it stands now, the Mendenhall is climbing toward its crest and warnings run through Thursday. If you live below a glacier-fed river or on any floodplain, set your leave-early trigger before the water reaches it, and keep a way to receive warnings that does not depend on the power staying on.
