For third time this year, Suicide Basin floods Mendenhall Lake

Jökulhlaup doesn’t raise alarm despite heavier rain in June

Water levels on Mendenhall Lake have risen this week due to a glacial phenomenon known as a jökulhlaup. (Courtesy the National Weather Service website).

The jökulhlaup has struck again.


Every summer since 2011, Suicide Basin, a glacial lake which feeds the larger Mendenhall Lake, swells with rain and melt water enough to lift the glacier, flooding the lake with water.

These sudden dumps are known by the Icelandic word jökulhlaup, which means “glacial run.” Built-up water floods out all at once or in stages. This year proved to be the latter case: at 11 a.m. Tuesday, Suicide Basin flooded Mendenhall Lake for the third time this year, causing a moderate increase in water levels.

Water levels crested Tuesday at about 6 feet over a U.S. Geological Survey baseline.

“This was a very small (jökulhlaup),” National Weather Service meteorologist Edward Leske said. “We’ve had one or two other years like this that we’ve had multiple releases instead of one big one.”

Rain levels have been higher than normal this June, topping 3.27 inches of precipitation over the average of 2.88 inches, Leske said. Historically, May and June are Juneau’s driest months. 1.4 degrees below normal for the month all due to cooler than normal daytime highs, relates to cloud cover.

The increase in water is nothing to worry about.

Minor flood stages don’t occur until flood levels reach 9 feet, Leske said. Then, waters from Mendenhall lake can flood a parking lot for Skater’s Cabin on the West side of the lake. Moderate flood stages occur at 10 feet, when the Mendenhall campground can flood with lake water.

Major flood stages, which NWS measures haven’t come within two feet of, occur when the lake gains 14 feet over the baseline. The highest measured water levels on Mendenhall Lake occured last year, when a jökulhlaup caused the lake to swell to 12 feet.

Jökulhlaup waters flow into Mendenhall River, increasing flow rates and serious erosion problems for a small group of riverside homeowners in the Mendenhall Valley. The City and Borough of Juneau is currently weighing its options on how best to help homeowners along Meander Way, where erosion is worst.

It’s hard to predict what’s normal for a Suicide Basin jökulhlaup, Leske said, as occurring since 2011, the sample size is small. Five of the 10 highest water levels measured on Mendenhall Lake have occured since 2011, when the Suicide Basic jökulhlaup started, according to the NWS website.

To monitor Suicide Basin levels in real time, visit the USGS Suicide Basin lake gauge and camera website, and to monitor the Mendenhall Lake gauge and forecast, visit the NWS website.

• Contact reporter Kevin Gullufsen at 523-2228 or


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