The fourth-largest outburst flood in Juneau’s history crested in August. Soon after, Eran Hood stood at the edge of an enormous empty basin in the mountains above the city.
Just a day or so before, the basin had been full of 16-billion gallons of water.
“This right here is the source of all the trouble in Juneau,” said Hood, an environmental scientist at the University of Alaska Southeast who has been coming to this spot for 15 years to study an annual flood triggered by rapid melting on the Mendenhall Glacier.
Glacial floods are increasingly dangerous around the world. Two weeks after Juneau’s flood subsided, a weakened ice sheet collapsed in the Himalaya and triggered catastrophic floods and landslides in Nepal.
Something similar is happening in Alaska.
Each summer, a natural reservoir that’s formed along the edge of the Mendenhall Glacier fills with water from melting ice. The glacial lake has an unfortunate name — Suicide Basin, likely a reference to the imposing terrain, Hood said.
Three of the basin’s sides are towering bedrock cliffs. The fourth side is formed by the glacier itself, which creates an ice dam that holds the water back most of the year. But as summer wears on, the pressure builds to a breaking point. The water eventually floats the glacier, and an icy torrent begins to slip beneath the ice.
“To me, it’s just stunning how different it is every time we come up here,” said Hood. After every flood, he races here with his drone to photograph the basin as soon as it empties. The camera captures images that form a 3D map to help predict how big the next flood will be.
Every so often during his drone survey, the sound of ice calving off the glacier echoes off the mountains. The area is still unsettled, Hood said, because 16 billion gallons of water just rushed toward Juneau from this spot. There wasn’t much damage this year, thanks in part to a new system of flood walls along the Mendenhall River. But in 2023, the outburst tore into the river banks and ripped homes into the raging water.
The next year, nearly 300 houses were swamped.
The scale of the problem becomes clear from this vantage point on the glacier, where streams of electric-blue meltwater carve deep moulins into the ice. The empty basin is a colossal chasm nearly a mile long and 500 feet deep.
“It’s something that most people in the world will never see or understand,” Hood said. “When I bring people here, they look out and say, ‘Oh my god, now I see what you’re talking about.’”
What was it like when the ice dam failed, and billions of gallons started slipping beneath the glacier toward Juneau?
“ It starts very slowly, the drainage, because when the water starts to force its way under the glacier, the channels that it’s moving through are very small, and as water moves through, the friction heats it up, and so it melts the channels larger.
“It starts as a trickle and ends as a torrent when that subglacial channel is probably the size of a subway tunnel, dumping water down to the toe of the glacier.”
How quickly is the glacier melting?
“ At the toe of the glacier, it’s retreating back 10 to 50 meters a year or more. But a lot of the volume that’s being lost from the glacier is because the whole lower part of the glacier is thinning. And so we see thinning rates around here of around four meters per year.
“If you walk to the edge of the glacier, go to the rock face, spray paint your name on there, you come back two years later, it’ll probably be 25 feet above your head. So right in this spot in the last decade, we’ve probably lost about 120 feet of ice.”
What role does climate change play here?
“ Alaska is actually, of anywhere on Earth, the mountain glaciers in this region are melting more rapidly than any other mountain glaciers. The reason for that is that we have a tremendous amount of ice at relatively low elevation where it’s pretty warm, and so we’re seeing thinning and retreat rates that are extraordinarily high, and there’s also a tremendous amount of ice.
“So, this is creating situations like the one we have here, but if we zoom out, we can also see that the glaciers in Alaska that are melting are contributing substantially to sea level rise.”
What is the solution?
“ There’s a lot of people who have ideas about the solution to this problem. One of the ideas that they’re pursuing is drilling a tunnel through the mountain so that during the summer, as water was flowing into the basin, it would flow down the tunnel and then discharge into Mendenhall Lake, and essentially bypassing the basin and not allowing it to fill.
“They would put a drain tunnel into the bottom of the basin. The logistics of that, as you can see from standing here, are extremely complex in terms of tunneling under, coming out in an environment where you’re coming out onto a rock face that’s covered with giant icebergs. You probably have to tunnel through a mile and a half of rock in the mountain to even get access to the basin.”
Why do you dedicate your life to this problem?
“ I live in Juneau, and I know people who live next to the river, and you see what an impact it is. I mean, before we had the flood walls, people were at the mercy of the floods, and people lost everything. They lost their cars. They lost their belongings.
“Being able to help protect people from that, help them to understand what’s at risk here and sort of the dynamics of this, is really important. We also hope that, because these lakes occur throughout Alaska, that we can take the program we’re developing here to other places that are going to be impacted by hazards like this in the future.”
When you’re standing at the base of this empty basin, how do you feel?
“ I’m still overwhelmed by it, because people come up with ideas all the time: ‘Hey, we could put a siphon. We can bomb the glacier and destroy the ice dam.’
“Then when you come up here and you see the scale and you understand it, you really understand what a complex engineering problem it will be to mitigate this natural hazard.”
This article was originally published on WBUR.org.
Copyright 2026 WBUR