It’s only a matter of time before the rising water in Suicide Basin can no longer hold and it forces its way underneath the Mendenhall Glacier, lifting up the ice so it can drain into the Mendenhall lake and river.
There’s no way to predict when the glacier lake drain — a relatively new phenomenon for Juneau known as a jökulhlaup — will take place, but officials hope it will be sooner rather than later given the potential flooding hazard.
“Basically the less water you have to worry about, the better it is,” City and Borough of Juneau Emergency Coordinator Tom Mattice said. “The less volume of water, the less we have to worry.”
The word jökulhlaup translates from Icelandic to “ice jumping up,” a reference to the rising water can float an ice dam — the Mendenhall Glacier in this case — so that the water can drain from below.
Suicide Basin, approximately 72,000 square meters large (the equivalent of 130 football fields), is located on the eastern side of Mendenhall Glacier roughly two miles up. It’s hidden from the view at the visitor center by Mount Bullard. It’s named after Suicide Glacier, which is located right above it in a valley between the mountain peaks. Some of the melt from Suicide Glacier contributes to the water in the basin.
Water levels in the basin have been rising steadily at about two feet per day since mid-June and surpassed 70 feet on Thursday, according to the National Weather Service which is monitoring the situation alongside officials from the city, the U.S. Forest Service, the U.S. Geological Survey and the University of Alaska Southeast.
That’s more than what the basin fill was in 2012 when the water levels topped out at about 52 feet before draining, but 70 feet is much less than 2011 basin fill levels. There wasn’t a sensor in the basin to gauge the water levels in 2011, the first year the jökulhlaup occurred, but officials were able to “do the math backwards,” as Mattice put it, and determined the basin fill was well above 100 feet when it broke based on the water flow of the swollen Mendenhall Lake and River.
“We’re above 2012 but we need double this amount of water to get to 2011,” Mattice said.
The unanticipated 2011 jökulhlaup caught Juneau residents off guard as the high river water flooded the streets, prompted an evacuation and caused some property damage. A sensor gauge, developed by a UAS graduate student, was placed in the basin after that. It transmits data to the NWS for monitoring purposes. The NWS puts the data online; it can be viewed at http://water.weather.gov/ahps2/hydrograph.php?wfo=pajk&gage=jsba2.
Brian Bezenek, the lead forecaster at the Juneau National Weather Service office, said once the water begins releasing this year, the NWS will issue a flood watch to alert the public. The NWS and other agencies will continue monitoring the situation and update their advisories should flooding be severe.
A NWS “watch” means there’s a potential hazard from a dangerous or life-threatening activity but nothing has happened yet, whereas an “advisory” and “warning” are more serious. An advisory means something has happened but there’s minimal risk to life and property, and a warning means there’s definitely a risk of damage to life and property.
It’s hard to tell whether this year’s jökulhlaup will be a glacier outburst — a dramatic gush of water bursting through the ice dam — or more of a glacier leak like last year’s, when water dribbled out over the course of the summer.
Either way, people will have plenty of time to prepare. It takes time for the lake and river to rise inches at a time, and it should take roughly 36 hours for the lake and river gauges start rising. The crest on the lake and river will likely be four days after the basin begins draining.
“We should have four days notice roughly before ... we get the peak on the river,” Bezenek said.
Residents in the river corridor who could be affected by flooding have been warned about impending deluge by the NWS and city officials. View Drive residents, considered the most vulnerable residential area since the Mendenhall River winds directly behind the properties, say they’ve taken steps to prepare for flooding, but they’re unworried since they’ve dealt with this three times in the past.
“Each of us has prepared in small ways but it’s not been a big deal,” View Drive resident Carol Habeger, 59, told the Empire earlier.
The U.S. Forest Service said they might close down the Mendenhall Campground, Nugget Falls Trail, Photo Point Trail and the road to Skaters Cabin if the water levels rise high enough. In the meantime, the Forest Service is asking people to be cautious in the park area. It advises kayakers and rafters to stay away from the face of the glacier, and hikers to watch for waves from calving and to “play it safe” at the terminus of Nugget Falls. The city advises anyone living along the river corridor to be prepared for flooding and to have a personal “go bag” of emergency supplies.
The jökulhlaup is expected to be an annual mainstay in Juneau because Suicide Basin is no longer being filled with ice. When the basin refills, it’s with liquid water.
Jökulhlaups are a relatively new phenomenon for Juneau, but it has been common for years on the British Columbia side of the Taku Glacier. Jökulhlaups from Tulsequah Lake and Lake No Lake in northwest British Columbia have occurred for years and 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.
• Contact reporter Emily Russo Miller at 523-2263 or firstname.lastname@example.org.