An unusual glacial lake drain left residents along the Mendenhall River a little nervous about just how high waters would rise.
Eran Hood, environmental science professor at University of Alaska Southeast, took a helicopter ride above the glacier to see where the outburst came from. What happened is called a Jökulhaup, where a body of water on top of or in a glacier has formed due to ice damming and it drains to its base. In this case, the base is the Mendenhall Lake.
“Basically that basin, by the time we got up there around 11:30 (a.m.) it had drained out pretty much completely,” he said.
They could see an outline of where water had been in the basin, but there was no water left. Hood said they determined water drained from Suicide Basin, which is on the eastern side of Mendenhall Glacier roughly two miles up.
“We just wanted to survey the size of the basin, to see if we could get an idea about the volume of water or determine if there was still water,” Hood said. “We won’t know exactly until the flood comes back down. The USGS website will have total flows. That will allow us to get a really nice calculation of how much water was stored in that basin.”
Hood said the basin is approximately 72,000 square meters large — the equivalent of 130 football fields. That doesn’t necessarily mean that much water was actually in the basin, given that there also is ice in it.
Aaron Jacobs, general forecaster and hydro focal points specialist with the National Weather Service Juneau office, also went on top of the Mendenhall Glacier Thursday. He said the department has been recording water levels at the river since 1995 and at the lake since 1984 and this is the second highest peak. Jacobs said there also wasn’t much of a difference.
“It’s going to recede very quickly. It should be below flood stage in the next three hours,” he said at 5 p.m. Thursday. “Everything is calming down as the lake has drained and the amount of water input is slowing. There is some (input), but its not as much.”
The most significant residential water flow occurred at View Drive, which had a “soft” closure late Thursday morning and reopened at 4 p.m. Waters rapidly rose early Thursday morning, cresting at just above 13 feet at 1:30 p.m., according to the National Weather Service. The river normally flows between four and five feet, according to U.S. Geological Survey data. The weather service also documented that Mendenhall Lake crested at just under 11 feet. According to a graph on the website, waters began rising late on Monday and saw the most significant growth Wednesday through the crest on Thursday. Water levels appear to be receding, but the flood warning remained in effect until 10 p.m. due to the uncertainty of the glacial release.
Tim Steffens, meteorologist with the Juneau Forecaster’s Office of the National Oceanic and Atmospheric Administration, said there was a remote chance ice could have plugged the glacial flow and more water could come down, but they largely expected waters to continue receding.
Ron Marvin, Mendenhall Glacier Visitor’s Center Director, said a lot of areas at the glacier park were flooded.
“We saw some fishes swimming among the trees,” he said. “We have been watching the water flow. The water was two inches from covering the bridge at Photo Point.”
That water activity flooded most of the Nugget Falls trail and submerged most of the vegetation throughout the area. The Moraine Ecology Trail also was closed.
Arctic Terns nest in that vegetation, but luck was apparently on their side.
“The birds’ timing was impeccable because they had flocked their chicks and had just taken off a few days ago,” Marvin said. “They all managed to get away in the nick of time.”
He said it would be interesting to see what affect the flooding has on wildlife once the waters recede.
Marvin said if they looked through their telescopes this morning they saw turbulent water by the face of the glacier and increased water flow from the waterfalls also on the face of the glacier.
Marvin said the National Oceanic and Atmospheric Administration told them that in 2007 a glacial lake drained, but it wasn’t nearly as big. Marvin believes it has only occurred twice now that NOAA is aware of with the Mendenhall Glacier.
Tom Mattice, city emergency coordinator, the Alaska State Troopers and U.S. Forest Service flew above the Mendenhall Glacier shortly after noon Thursday to see if they could locate the source of the water flow and how much was left to drain.
“It looked like the basin underneath Suicide Falls there has got a lot of ice in it,” Mattice said. “It appears it filled up with water and let loose. You can see how the snow and ice have settled back down in that region. You can see water line marks around the basin. You can tell that that basin was full of water. It was just like pulling the cork in a glass of ice cubes. We tried to gain an estimate of the size of the basin and the depth of the water. We’re going to be looking at some long-term monitoring programs so we can keep an eye on it and monitor it in the future. Obviously you don’t want to be surprised by this in the future. It would be nice to know when we are getting to critical stages.”
Mattice said this kind of glacial activity is common with the Taku Glacier.
City staff also worked closely with the rising waters near residences and trails throughout the day. The city closed several trails and strongly urged people to stay off them, since the river banks are unstable.
Residents of View Drive were also strongly encouraged to evacuate. City Manager Rod Swope said the reason was largely because residents would have been isolated because water had flowed over the road and power was shut off. Water had halfway submerged a piece of power equipment. By mid-afternoon only one of about a dozen residents on View Drive had elected to stay.
City departments had patrolled riverside neighborhoods to watch for additional floodwaters creeping up on homes, but the biggest concern was View Drive. The other area closed off was Mendenhall Campground, which saw floodwaters breach Skaters Cabin Road about 6:30 a.m. That remained closed on Thursday. Jacobs said the Forest Service will keep the campground closed until the weekend so it can assess damages.
The Public Works Department also sealed off a pump along view drive. Bill Cameron, a wastewater department operator, said if water were to go over it, that would fill the pump and end up backing wastewater and floodwater into homes.
Hazel Reynolds, supervisor for the valley street department, said the road has flooded before, but typically it’s in October with high tides and heavy rains and the road coverage usually only lasts a few hours.
The glacial-colored waters breached the road around 9 a.m.
“There’s been some significant icebergs floating down the river this morning,” she said. Reynolds had gone door-to-door encouraging people to leave and updating them on the issue.
Some View Drive owners were more concerned than others.
Susana Hurtte lives on View Drive with her family. She biked across the flooded road to retrieve items from her home. She said their trampoline, her sister’s playhouse and their electric greenhouse were completely submerged.
“From just this morning ‘til 12:30 (p.m.) it’s already (risen) a ton,” she said. “Keep everybody whose houses are along the river in your prayers.”
She said there’s about 6 feet until water could reach the entrance of their house, and if water kept rising at the rate it did Thursday morning they’d be in trouble, although that fear never came to pass.
One resident, who declined to be identified, said the last time water levels had been close to this height at View Drive was in 1996, although Thursday’s levels were about six inches lower. He said this is the first time the flood waters have been from a glacial burst. “To me this is more panic than reality,” he said.
Ernie Mueller, with the Juneau Red Cross, said he went down to View Drive twice Thursday afternoon and other than floodwaters breaching a garage there was no significant damage. He said people seemed to be doing OK and no one requested further Red Cross assistance.
Residents, city staff and Forest Service staff began noticing waters maintaining levels and even decreasing between noon and 1 p.m. Water levels began to drop more significantly throughout the afternoon and View Drive reopened about 4 p.m.
Mattice said some homeowners had called him back and said water levels were dropping rapidly, about a foot per two hours, though he could not confirm the water recession rate.
People should “continue to stay away from the banks of the river because they’re soft,” he said. “They’ve been undercut and flooded. The riverbanks themselves are going to be questionable for a while.”
• Contact reporter Sarah Day at 523-2279 or at firstname.lastname@example.org.