Evacuations are underway in parts of Alaska’s capital of Juneau after a glacial outburst sent water rushing down the Mendenhall River into areas in the region, which is expected to cause major flooding. The flooding is being caused by a “glacier-dammed lake outburst” (GLOF) which occurs when a lake dammed by ice or a glacial deposit gives way and releases heavy amounts of water into river systems further downstream.

The city and borough of Juneau announced that it “is aware of the presence of water in certain areas” and that anyone within the flood zone of the Mendenhall River should evacuate the area. A Facebook post read: “A glacial outburst has occurred at Suicide Basin. The basin is releasing and flooding is expected along the Mendenhall Lake and River.”

Officials have recommended that residents within the 17-foot lake level inundation zone evacuate the area until the water recedes and an “All Clear” message is sent via the wireless emergency alert system.  The Federal Aviation Administration (FAA) also issued a temporary flight restriction (TFR) around the area.

The National Weather Service (NWS) office in Juneau issued a Flood Warning for the Mendenhall River and said that as of early Wednesday morning, the river was over 15 feet and was continuing to rise: “Our forecast right now, we’re starting to think that we’re going to crest, we were messaging 8 a.m. though 12 p.m., we’re thinking our crest might be closer to 8 in the morning and might be closer to the higher end of the spectrum,” with forecasters estimating that the river was expected to crest between 16.25 feet and 16.75 feet.

Suicide Basin is a side basin of the Mendenhall Glacier above Juneau. Since 2011, the NWS said Suicide Basin has released glacial lake outburst floods that caused inundation along Mendenhall Lake and River annually with a record flooding event taking place on Aug. 6, 2024, that had caused the river to reach a then-record level of 15.99 feet. As of 10 a.m. EDT Wednesday, the river had already reached 16.17 feet and was still rising. The flood warning is scheduled to remain in effect until 12 p.m. EDT on Thursday.

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