In the early hours of August 6, a lake dammed by Juneau’s Mendenhall Glacier burst through the ice, flooding hundreds of homes and businesses in the Mendenhall Valley where many of the Alaskan capital’s residents live. This outburst led to the largest flow ever recorded in the Mendenhall Basin and surpassed last year’s historic flood levels, with an estimated 16 billion gallons of water—enough to fill more than 32,000 Olympic-sized swimming pools—draining into the river.
Flooding peaked early in the morning on August 6, reaching a whopping 15.99 feet—three times the river’s usual height. While city officials initially estimated that about 100 homes were affected, that number has jumped to over 300 as assessments continued. Some residents experienced only minor damage, while others had foundations damaged and severe water damage to their belongings, homes and cars. Alaska Governor Mike Dunleavy declared a state disaster emergency shortly after Juneau declared a local emergency on August 6. Two days later, Dunleavy visited Juneau along with Senator Lisa Murkowski to speak with affected residents and city officials.
Glacier lake outburst floods (GLOFs) can occur when rain and meltwater build up behind ice dams until the water pressure grows strong enough to burst through, causing the lake to drain rapidly; they can also happen as a result of large chunks of ice falling into lakes at the base of glaciers. These floods have become more common as a result of human-induced climate change causing rapid melting of glaciers around the world.
Two miles from the terminus of the Mendenhall Glacier, ice blocks Suicide Basin, a valley that the Suicide Glacier formerly filled, but which is now open space because the glacier has retreated significantly. The basin now fills with rain and meltwater every summer due to climate change and glacier recession. This water slowly erodes a tunnel in the ice dam each year before eventually breaking through and draining rapidly, as can be seen in this time-lapse video.
GLOFs originating from Suicide Basin have occurred annually since 2011, sometimes more than once in a single year, so residents knew another flood was likely on its way. However, flooding has worsened in recent years, with record flood levels being set both last year and this year. Monitoring has improved substantially on the basin, providing residents with early flood warnings, which is critical for communities like Juneau, according to Jeffrey Schlegelmilch, the director of the National Center for Disaster Preparedness at the Columbia Climate School. “Better understanding of the strength of the barriers containing the water and likelihood of rupture or other triggers of flooding will help with early warning to communities,” Schlegelmilch told GlacierHub. These early warnings are critical for residents to get somewhere safe, but property damage remains a problem.
Various solutions have been proposed to reduce flooding in the future, including bombing the ice dam and creating permanent tunnels, but issues with feasibility, cost and the low chance of success have stopped these conversations from developing into action.
For now, Juneau residents are cleaning up after this flood while trying to prepare for the next one. In the short term, many city and disaster assistance programs have been helping residents rebuild. City officials are working on improving hazard zone maps, and residents can apply for state assistance for house repairs and personal property damage, though last year’s flooding proved that these funds were often insufficient for the extent of repairs needed.
Flood insurance can help those who have it, but residents are not required to purchase policies. According to a state report published in 2023, only 745 households in the entire state of Alaska had flood insurance. And even those with flood insurance or homeowners insurance can sometimes find themselves paying out-of-pocket for damages. This divide between individuals who can afford to prepare and recover from these hazards is key for predicting inequalities in preparations and disaster planning, according to Schlegelmilch.
“Unless there is a conscious effort made to address equity in resilience, [floods] and other disasters will widen inequalities in the communities impacted,” Schlegelmilch said.
While water levels have returned to normal, the lives of many Juneau residents have not and will not for some time, reflecting the struggles of millions around the world living in close proximity to glaciers that are rapidly shrinking due to climate change.
