Juneau Dodges Major Flood as Emergency Barriers Hold Against ‘Glacial Outburst’

Record Flood Threat Contained

Juneau, Alaska, narrowly avoided major damage this week after a glacial outburst flood sent record volumes of water down the Mendenhall River. Emergency officials say newly installed HESCO barrier walls successfully contained most of the surge, with only scattered reports of seepage and minor water leaks.

The river peaked at 16.65 feet, topping last year’s record, but water levels began receding without catastrophic breaches.

What Caused the Flood?

The event was triggered by a sudden release of water from Suicide Basin, a side basin of the Mendenhall Glacier. Meltwater had been trapped behind ice and rock until pressure forced it to burst, a process known as a glacial lake outburst flood (GLOF).

These floods have become an annual hazard for Juneau since 2011, growing more severe as climate change accelerates glacier retreat.

Emergency Response and Success

• Early Warnings: Over 1,000 residents were urged to evacuate ahead of the crest.
• Protective Measures: About 10,000 interlocking sand-filled HESCO barriers formed a 2.5-mile levee system designed to handle an 18-foot crest.
• Outcome: No levee failures were reported, though pumps were used to manage minor leaks.

Local officials hailed the operation as a proof of concept for stronger permanent defenses.

Looking Ahead

Experts warn that these outburst floods are likely to continue for decades, as long as the ice dam at Suicide Basin remains intact. Permanent infrastructure—such as engineered levees or controlled drainage systems—is now under discussion.

FAQs

Q: What is a glacial outburst flood?
A sudden, often violent release of meltwater from a glacier-dammed lake, capable of sending billions of gallons of water downstream.

Q: How high did the river get?
It reached 16.65 feet, the highest on record for the Mendenhall River.

Q: Were there any major damages?
No major structural failures occurred thanks to the barriers, though some localized flooding and road closures were reported.

Q: Will this happen again?
Almost certainly—it’s been happening annually since 2011, and climate conditions make it more likely in the coming decades.

Q: What’s the long-term fix?
Authorities are considering permanent levees, flood channels, or managed releases from Suicide Basin.

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