Catastrophic Juneau Floods: Historic Glacier Outburst Sends Water Surging Through Alaska’s Capital

Juneau, Alaska—Residents along the Mendenhall River awoke Wednesday to sirens and cellphone alerts as a glacial-lake outburst from Suicide Basin pushed water levels to the highest mark ever recorded, overtopping protective berms and forcing rapid evacuations in Alaska’s capital. By 7:15 a.m. local time, the National Weather Service measured Mendenhall Lake at 16.65 feet—well above the previous 2016 record—and issued a rare “Extreme Flood Warning,” advising anyone in low-lying neighborhoods such as Riverside Drive, View Drive and Jordan Creek to seek higher ground immediately. Drone video showed chunks of ice, whole trees and propane tanks barreling downstream as the swollen Mendenhall River ripped away sections of riverbank and threatened the Brotherhood Bridge and adjacent power lines. City officials opened emergency shelters at Thunder Mountain High School and Tlingit & Haida Community Council Hall, while Alaska Electric Light & Power pre-emptively cut electricity to roughly 2,300 customers to prevent electrocution hazards. “This is an unprecedented hydrologic event for Juneau,” city manager Katie Koester said at an afternoon press briefing. “Infrastructure we built for a 100-year flood is being tested by a 500-year flood.” The trigger is Suicide Basin, a side pocket of the rapidly retreating Mendenhall Glacier that periodically fills with meltwater and then bursts through ice dams—a phenomenon scientists call a glacial-lake outburst flood (GLOF). Satellite analysis shows the basin held nearly 40% more water this summer than in any previous year on record, thanks to a hot, wet July and accelerated ice melt driven by above-average ocean temperatures in the Gulf of Alaska. Climate researchers warn that GLOFs are becoming more frequent worldwide as glaciers thin. “We’re seeing the climate signal loud and clear,” said University of Alaska Fairbanks glaciologist Dr. Eran Hood. “Each year Suicide Basin is bigger, and the resulting Juneau floods put more people and property in harm’s way.” Although no fatalities were reported as of Wednesday evening, at least 23 homes suffered major damage, including two riverfront houses that collapsed when the bank beneath them eroded. City engineers estimate preliminary losses at $12–15 million, a figure expected to rise once inspectors can safely access the flood zone. Governor Mike Dunleavy activated the Alaska National Guard for sandbagging and search-and-rescue. The Federal Emergency Management Agency pre-positioned supplies in Anchorage and said a disaster declaration request is “imminent.” Glacial silt has already clogged municipal water-intake screens, prompting a boil-water notice citywide. Residents who must travel are urged to avoid Mendenhall Loop Road, where shoulder washouts have narrowed traffic to one lane. Authorities advise keeping go-bags ready with three days of food, water and medications, in case renewed releases from Suicide Basin extend flooding through the weekend. Looking ahead, the U.S. Army Corps of Engineers is studying a permanent diversion tunnel that would gradually drain Suicide Basin before it ruptures, similar to projects in Iceland and Peru. Funding, however, remains uncertain amid federal budget negotiations. For now, Juneau’s focus is survival and cleanup. “Our community has weathered avalanches, earthquakes and pandemic,” Mayor Beth Weldon said. “We’ll get through these Juneau floods, too—but we can’t ignore the climate trends that keep raising the stakes.”