Alaska’s Capital Flooded By Melting Glacier

This particular glacier has made outburst flooding a habit; the floods occur when a glacial lake, hemmed in by an ice dam, gets too high and suddenly drains. According to the US Geological Survey, the outbursts started in 2011, “occur annually, and reached record levels in 2023 and 2024.” Last year, around 300 homes were damaged by the flooding; though authorities have installed various flooding mitigation measures, it might be worse this year. Governor Mike Dunleavy has issued a State Disaster Declaration “in response to an imminent threat of catastrophic flooding.”

The Mendenhall glacier is part of the Juneau Icefield. A 2024 study found that ice loss across the field doubled after 2005 compared to the previous few decades. “Thinning has become pervasive across the icefield plateau since 2005, accompanied by glacier recession and fragmentation,” the authors wrote. Another study, from 2020, found that the ice dam holding the lake back thinned by twice its reference rate in 2018-2019 alone; things have gotten worse since then.

Glaciers everywhere are doing that sort of thing, of course. Juneau is facing it down today, but many millions of people are situated under potential glacial catastrophes in other parts of the world, in particular in northern India, Nepal, and Pakistan, as well as China and Peru. In 2023, 15 million cubic meters of “frozen lateral moraine,” essentially melting permafrost, fell into South Lhonak Lake in the Indian state of Sikkim; it generated a 65-foot-high wave that overtopped the lake’s boundaries, sending debris and water miles downhill. It destroyed a hydroelectric dam, damaged or washed away tens of thousands of buildings including more than 30 bridges, and killed dozens.

Monitoring like that going on in Alaska can obviously mitigate the danger, but not every part of the world enjoys similar resources. That’s how the slow-drip process of melting ice can manifest as an acute and terrifying catastrophe; slowly, then all at once.