What is a Glacier Outburst and is Alaska’s Juneau at risk? Read!

A rare and potentially dangerous geological event is unfolding in Alaska, as a glacier outburst flood is underway near the capital city of Juneau. This event, officially known as a glacial lake outburst flood (GLOF), involves a massive amount of meltwater suddenly being released from a basin dammed by a glacier. While such floods have been an annual occurrence in the region for over a decade, officials have warned that this year’s floodwaters could set new records, posing a significant risk to residents and infrastructure in the Mendenhall Valley. This article provides a factual look at the cause of this natural phenomenon, the specific risks to Juneau, and why these events are becoming more frequent.

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What is a glacier outburst and is Juneau at risk?

A glacier outburst is the rapid release of water from a glacial lake that is held back by a dam of ice or moraine. In the case of Juneau, the Mendenhall Glacier acts as an ice dam for a basin called Suicide Basin, which fills with rainwater and snowmelt each spring and summer. When the water pressure becomes too great, it forces its way under or around the ice dam, creating a flood.

Yes, Juneau is at risk. While temporary flood barriers have been installed, officials have urged residents in the Mendenhall River valley to evacuate as the river is expected to crest at record-high levels. This is the third consecutive year of record flooding, and the event has previously caused homes to be swept away and hundreds of residences to be swamped.

Why are these glacier floods becoming a recurring problem?

These annual glacier floods are a consequence of the region's changing climate. As the Mendenhall Glacier and its neighbors retreat and thin, they leave behind depressions in the land, such as Suicide Basin. These basins fill with water, but the Mendenhall Glacier still serves as an ice dam, creating a ticking time bomb. The increasing frequency and severity of these floods are directly linked to higher temperatures causing more rapid glacial melt. Researchers from the University of Alaska Southeast predict these outburst floods could continue for decades as the glacier continues to thin and retreat.

How can residents stay safe during a glacial outburst flood?

Residents in affected areas must follow all official guidance from the City and Borough of Juneau and the National Weather Service. The primary safety measure is to evacuate to higher ground when an official warning is issued. Staying away from the Mendenhall River and Mendenhall Lake is critical, as the floodwaters can be swift, turbulent, and carry dangerous debris. People should monitor local news and official sources for real-time updates on water levels and evacuation orders to ensure their safety and that of their families.

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Conclusion

The glacier outburst currently underway is a powerful and dangerous natural event with significant implications for Juneau, Alaska. This phenomenon, driven by the retreat of the Mendenhall Glacier, underscores the tangible effects of climate change. While the city has implemented some protective measures, the ongoing evacuation orders highlight the severe risk to the community. As these glacial lake outburst floods are predicted to continue for decades, they serve as a stark reminder of the need for both short-term preparedness and long-term solutions to adapt to a changing environment.