Record-Breaking Alaskan Glacier Outburst Flood Averted by City’s Flood Barriers and Army Corps of Engineers Efforts

In Alaska, the Mendenhall Glacier’s adjacent lake, Suicide Basin, experienced a third consecutive year of water outburst, posing a potential threat to Juneau, the state’s capital city. However, the city’s flood prevention measures effectively averted a catastrophe this week despite record-breaking water levels.

The glacial lake forms as the glacier melts and retreats, accumulating rain, snow, and ice over the summer. When it reaches capacity, the lake escapes its icy confines of the Mendenhall Glacier, releasing a torrent into Mendenhall Lake and subsequently surging down the Mendenhall River.

This year’s event commenced on Tuesday, with the river exceeding its previous record high level of 15.99 feet by Wednesday morning after a rapid rise of over 7 feet in less than 24 hours. The peak was recorded at an unprecedented 16.65 feet, according to weather service reports, well above the previous record set just last August. By mid-afternoon, the river had decreased to 10 feet, with minor flooding persisting into Wednesday evening before normal levels are expected to resume by Thursday.

Last year’s event resulted in catastrophic flooding that affected over a hundred homes in Juneau, which officials deemed “unprecedented.” This year, the river level surpassed that of 2023 by a full foot.

In response to past floods, authorities have installed a flood barrier in vulnerable areas where approximately 1,000 residents and businesses reside. Additional resources, including around 37,800 feet of HESCO barriers and over 100,000 sandbags, were employed this year to fortify these defenses.

HESCO, a company specializing in barrier systems, has been collaborating with the US Army Corps of Engineers to monitor these reinforcements. City Manager Katie Koester praised the HESCO barriers for successfully protecting the community, stating that without them, hundreds of homes would have been flooded. Despite some water seepage, the barriers have remained intact thus far.

Though no incidents or rescues related to the water have been reported as of Wednesday afternoon, residents are advised to avoid flooded areas until the situation can be assessed by emergency crews. Alaska Governor Mike Dunleavy issued a preemptive disaster declaration on Sunday to streamline emergency response efforts, aiming to minimize impacts and preserve community safety.

Juneau, with its population of approximately 33,000 according to the US Census Bureau, is surrounded by coastal waters to the west and south. The city has been experiencing annual glacial lake outbursts since 2011, with events worsening each year since 2023. These occurrences are a consequence of climate change, as rising temperatures cause glaciers to thin or melt entirely, with the Mendenhall Glacier and Suicide Basin seeing significant reduction in size.

Recent studies have revealed that between 10 and 15 million people globally are at risk from impacts of glacial lake outburst flooding like what’s currently unfolding in Juneau. The world’s warming has resulted in the rapid melting and expansion of glacial lakes worldwide, increasing the likelihood of future outburst flooding events.