Glacial Outburst Flood

Question

We will be arriving in Juneau (via plane, not cruise ship) on the 16th of this month. I have been reading about the potential for glacial outburst flooding in the Mendenhall Valley. I have checked with the owners of the houses we have rented and both assure me they are not located in the area at risk. What I can't seem to find is information on how it impacts visiting Mendenhall Glacier. I read once the flood is underway they close the access roads, but wondering if it is currently "open" to visitors? Do they close access when they think a breach is imminent or not until it actually happens? If it does flood, about how long before it subsides enough to reopen access to the Visitor Center/Glacier? We would have an opportunity to go to Mendenhall Glacier on either the 17th or the 22nd, so am hoping one of those days we can get to it. Also, what is the best website to find up-to-date notices on whether access to the glacier is allowed or not? Hoping if it does happen, there is minimal effect for the residents. It sure sounds like authorities are trying to be proactive. TIA

Answer

The Mendenhall Glacier area near Juneau is subject to periodic glacial outburst floods, also known as jökulhlaups. These events occur when meltwater trapped in a glacial lake is suddenly released, sometimes rapidly increasing the water flow in Mendenhall Lake and the surrounding river valleys. While the risk exists, the local authorities actively monitor conditions to protect residents and visitors.

Regarding visitor access:

Access roads to the Mendenhall Glacier Visitor Center and the Glacier itself may be temporarily closed if authorities anticipate a flood or once a flood begins. Closures are typically precautionary, based on monitoring of water levels and glacial activity, not just after a breach has occurred.
During an active outburst flood, closures can last several hours to a couple of days, depending on the severity of the flood and how quickly water levels recede. The Visitor Center and trails are usually reopened as soon as it is deemed safe.
Authorities aim to minimize disruptions for both visitors and local residents. Since you are staying outside the at-risk area, your accommodation should not be directly affected.

For planning your visit:

Check for updated notices on road and trail access before heading to the glacier. The official sources are the US Forest Service Tongass National Forest Mendenhall Glacier page and the City and Borough of Juneau alerts.
If you are flexible, consider visiting either the 17th or 22nd, monitoring conditions closer to your chosen day. Early morning visits are often less affected by sudden closures and tend to have lighter crowds.
Phone numbers or email alerts from the US Forest Service can also provide real-time updates if you need last-minute information on trail closures or safety advisories.

In summary, access may be restricted temporarily if a flood is imminent, but closures are proactive and safety-driven. Keeping an eye on official Forest Service updates will help ensure you can plan a safe visit to Mendenhall Glacier while minimizing the risk of encountering a closure.

Glacial Outburst Flood

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