It is a phenomenon that has been common for years on the British Columbia side of the Taku River. But the jökulhlaup is set to become a Mendenhall Valley mainstay, if experts’ expectations hold true.

Suicide Basin has now filled and emptied for two years in a row, raising water levels on Mendenhall River and Mendenhall Lake. Though homes escaped unscathed last week as water crested well below the flood stage, last July saw minor to moderate flooding across parts of the Mendenhall Valley and forced the closure of the Mendenhall Lake Campground.

Eran Hood, associate professor of environmental science at the University of Alaska Southeast, said it is no fluke that this previously unusual event has now happened in two consecutive summers.

“There’s pretty good reason to believe that every single year, that basin’s going to fill up,” Hood said.

“Jökulhlaup” is the Icelandic term for the drainage event, also known as a “glacier dammed outburst flood.” It occurs when water fills up a glacial or subglacial lake basin to the point where the ice dam holding it back is forced aside.

National Weather Service hydrologist Aaron Jacobs said glacial retreat means Suicide Basin is no longer being filled with ice. When the basin fills, it now fills with liquid water, which eventually builds to the point where it can no longer be contained. In these drainage events, the water lifts up the Mendenhall Glacier in order to flow into the lake below.

The Suicide Basin jökulhlaup last week poured water into Mendenhall Lake from beneath the ice. Last July, it caused a dramatic gush of liquid water from the glacier’s flank into the lake.

“The movement of the glacier itself … changes its drainage path,” Jacobs explained.

In northwestern British Columbia, jökulhlaups from Tulsequah Lake and Lake No Lake have occurred for years. Those discharges often cause the Taku River, which flows into Stephens Passage on the Juneau side of the border, to swell and occasionally overspill its banks.

“Geographically, it’s almost the same kind of side basin off of the main (glacier),” said Jacobs, comparing Lake No Lake to Suicide Basin. “From looking at the correlation between the geography of where this is situated relative to the Mendenhall Glacier as pretty much identical to what Lake No Lake is in reference to Tulsequah Glacier, there’s a high probability that (the Suicide Basin jökulhlaup) will happen at least once a year.”

Now that the Suicide Basin jökulhlaup is an established phenomenon, Hood said university researchers are planning to install equipment to keep closer tabs on the basin — perhaps as early as this week.

“What we want to do is we want to put in a lake-level sensor (at Suicide Basin) as a pressure sensor, so that will show us the lake filling up, and also we’ll know exactly when the lake starts to drain,” Hood said. A fixed camera to take time-lapse photographs is also planned, he said. “That will be able to show us the thing bulging up and filling up,” he explained.

Jacobs said the equipment would help “better forecast the peaks,” as well as monitor when the basin fills up, when it begins to drain and how much water it is releasing into the lake.

“It’s going to be very important for us to have this,” Jacobs said.

Those monitors will not be able to determine how much ice is in the basin, Hood said, but another tool might work.

“In theory, we could take a radar up there and try to measure the ice thickness,” said Hood. “I’m not sure when or if we’re going to be able to pull off getting a radar up there, but it’s something at least that we’ve talked about.”

• Contact reporter Mark D. Miller at 523-2279 or at mark.d.miller@juneauempire.com.