Skip to main content
U.S. flag

An official website of the United States government

In 2011, Juneau residents were surprised by a historic flood on a clear sunny day – its first glacial outburst flood. As the community learns to live with the now-common phenomenon, a multi-agency group of researchers supported by the Alaska CASC works to understand how climate change contributed to the new hazard and how the community can anticipate and mitigate the effects moving forward.

Every summer in the four years leading up to her retirement, U.S. Forest Service park ranger Laurie Craig started and ended her day the same way: checking the Juneau National Weather Service website. Not to see the forecast or to look for rain, but to monitor the Suicide Basin water level. 

“The gauge would be the first thing I'd look at on my phone when I woke up and the last thing I'd check at night,” Craig says. “You’d see this line of the lake level creeping up, creeping up, creeping up, and then eventually it drops really fast.” 

“That's when you have to start worrying.” 


Hidden Water 

 A map showing the location of Suicide Basin in relationship to the Mendenhall Glacier and the city of Juneau. In the top right, a glacier sits high in the mountains above the curved Suicide Basin, which is blocked on its other side by the Mendenhall Glacier. The Mendenhall Glacier fills the valleys between the mountains and ends at the edge of the Mendenhall Lake. At the far side of the lake from the glacier, the Mendenhall River flows down the slope and along the left edge of the city of Juneau.
As the smaller Suicide Glacier in Juneau, Alaska rapidly receded away from the large Mendenhall Glacier, it left behind a barren, rock- and iceberg-filled basin. Rainwater, ice, and glacier meltwater accumulate in the basin, cupped between the Mendenhall Glacier and the bare mountain. When the water level reaches a certain threshold, it builds up enough pressure to force its way underneath the Mendenhall Glacier, draining into the Mendenhall Lake in a glacial outburst flood. As the lake overflows, the floodwaters inundate roads and homes, eventually making their way down the Mendenhall River and to the ocean.

As an icefield community, residents of Juneau, Alaska are used to living with glaciers. The Mendenhall Glacier is the backdrop of their lives – the site of wedding photos and team portraits, a popular hiking and skiing destination, a place of pride to take out-of-town visitors.  

But in 2011, when a historic 100-year flood appeared on a clear sunny day, the Juneau community saw a new side of its glaciers.  

“The river just went crazy,” says Eran Hood, Environmental Science professor at the University of Alaska Southeast. “It was going up and up and up and everyone was like, ‘Oh my God, what's happening? There's no rain, there's nothing!’ And if you went online and looked at the [National Weather Service flooding forecast], it was just flat.” 

“We weren't really sure where the water was coming from,” says Tom Mattice, Emergency Programs Manager for the City and Borough of Juneau. “Aaron Jacobs [from the National Weather Service], Eran Hood, and myself flew up to Suicide Basin, thinking that that's where the water had come from. And, sure enough, the basin had drained, it was just a big empty swimming pool full of ice cubes.” 

From their helicopter, the men learned the truth. The lake filling Suicide Basin had reached some unknown threshold and suddenly drained like a bathtub, flowing underneath the Mendenhall Glacier and flooding the Mendenhall River and a nearby neighborhood. Juneau’s first glacial outburst flood.  

Sixty years ago, the mountains behind Juneau were encased in ice. The massive Mendenhall Glacier filled the valleys, joined by an offshoot Suicide Glacier crystalized between two peaks. As temperatures warmed, the smaller Suicide Glacier retreated rapidly, leaving behind a baren basin sandwiched between the shrinking Mendenhall Glacier and the mountains. Here, rainwater, glacier meltwater, and ice collected over time until… 

“The main issue is that these smaller glaciers are responding more rapidly to a changing climate,” says University of Alaska Fairbanks research professor Gabriel Wolken. “These smaller glaciers are retreating up and, in their place, they leave a landscape that has been modified by [ice] over time.” 

Glacial outburst floods were a new phenomenon for Juneau but are here to stay. Since the first event in 2011, there have been glacial outburst floods in Juneau every year, with as many as ten smaller outbursts in a single year. The floods inundate campgrounds and homes and threaten infrastructure along the river. 

“The vast majority of the glacial outburst floods have been 100-year floods,” says Mattice, referring to severe floods that only have a 1% chance of happening at any time of the year. “In a period of ten years, to have ten 100-year floods, that's unusual.” 


Partnership-Based Research 

A path near the Mendenhall Glacier Visitor Center in Juneau, Alaska is completely submerged by floodwaters from a glacial lake outburst flood.

After the first flood, the Juneau emergency management community immediately recognized the need for science and tools to understand this new hazard. Their first priority: predicting the next flood. 

“The problem was, the hydrologic models [the National Weather Service] used to forecast floods were almost entirely based on rainfall and had no mechanism to say, ‘Oh, there's a glacial outburst flood happening,’” Hood explains. “That just didn’t compute in their model.” 

As a result, the community couldn’t anticipate the next glacial outburst flood or predict how severe it was going to be. This also created new worries of mega floods, where if the glacial dam broke during a heavy rainstorm, the two flood events could combine into one major disaster.  

“The National Weather Service monitors everything from the weather that would normally produce flooding, from heavy rain to high freezing levels with rapid snow melt,” says Aaron Jacobs, Senior Service Hydrologist for the National Weather Service in Juneau. “But there are a lot more unknowns with glacial outburst flood events.” 

“They're something the Weather Service didn’t have a lot of expertise in during those first few years.” 

Fortunately, Alaska is home to a tight-knit community of natural hazards professionals, including the University of Alaska system, the USGS, the National Weather Service, and the City and Bureau of Juneau. Many of the key players in the glacial outburst flood research, including Mattice, Hood, Wolken, Jacobs, and Jamie Pierce, a USGS Hydrologist, had already worked together for many years on avalanche work. 

“The Suicide Basin project is a perfect example of why partnerships are so important,” Mattice says. “We couldn't have done anything without the amazing group of people that's been working together on this since the beginning.” 

The major research element of this effort was funded by the Alaska Climate Adaptation Science Center (Alaska CASC), a USGS program that helps communities and resource managers in Alaska understand and adapt to climate change.  

“Alaska is seeing warming at a faster rate than other parts of the United States and experiencing the impacts of climate change in ways that are quite dramatic,” says Alaska CASC Director Stephen Gray.  

“The way these ecosystems look and function is very much controlled by the frozen component of the system. There's growing concern about what landscapes that have been dominated by glaciers are going to look like in the future and how these ecosystems are going to function when they are no longer covered by massive amounts of ice.” 

The center follows the broader CASC model of co-production, research that prioritizes partnership involvement at all stages to ensure the final products are useful and useable to on-the-ground conservation and management. When selecting the glacial outburst funding proposal, Gray was particularly excited about the research team’s existing cross-agency partnerships. 

 “This project offers us a way explore co-production approaches in a situation where multiple state, federal, and municipal interests are involved,” says Gray. 

The project supported by the Alaska CASC allowed the Juneau flood research team to expand and coordinate their efforts. 

“Once we got that funding from the Climate Adaptation Science Center, that's when everything came together,” says Hood. 

“We were able to get other input from many different agencies [using] funding that was dedicated to this project,” Wolken says. “And if you look at the list of different agencies, it's quite large - the universities of course, the U.S. Geological Survey, NOAA, the National Weather Service, the Municipality of Anchorage, the City and Borough of Juneau.”  

“So, I think it really is a really great example of co-production.” 


Unraveling the Unknowns 

Snow and ice are visible at the bottom of a barren basin surrounded by sheer rock walls and glaciers.
Ice, rainwater, and glacier meltwater fill Suicide Basin, the former location of the now-receded Suicide Glacier, over the course of the year. Once the water level reaches a certain threshold, the water drains from the basin in a glacial outburst flood. Viewed during a helicopter flyover.

With their CASC support, Hood and Wolken led efforts to monitor conditions within Suicide Basin and create new models to forecast glacial outburst floods. It wasn’t easy. Just getting to Suicide Basin requires a helicopter and the iceberg-filled lake is steep, rocky, and constantly changing.  

“It's a really challenging place to work,” Hood says. “It involves a fair amount of technical rope work, which most field sites don’t.”  

Jacobs agrees. “Even though it is close to Juneau, it's still difficult to get up there. And the weather doesn't always work out for us to be able to do what we need to do. Trying to get equipment to work, dealing with big rocks and moving ice -- it’s a challenge.” 

But through perseverance, some lost equipment, and the expert mountaineering skills of USGS scientist Jamie Pierce, the team installed a sophisticated set of monitoring equipment in the basin that provides real-time information about the water level. 

“We have this whole suite of tools,” Hood says. “We’ve installed water level sensors, which allow us to track the level of water in the basin as it builds up. We've installed time lapse cameras, which allow us to visualize the basin filling. We use drone images [to create] digital topographic maps.” 

With this new data stream, Hood, Wolken, and their then-postdoctoral researcher Christian Kienholz worked with Jason Amundson, a glaciologist at the University of Alaska Southeast, and researchers with the National Weather Service to develop models predicting when the lake would reach its “flood-stage” height. This too was unexpectedly complex. Because the lake always contains a layer of ice and icebergs, the researchers couldn’t measure how deep it actually was, or even see the bottom when it was “empty.” As a result, Keinholz had to develop a new method to use drone photographs to build three-dimensional models of the floating icebergs to subtract them from the total estimated water volume. 

The researchers summarized their flood forecasting models on the Juneau National Weather Service Suicide Basin flood forecasting webpage, which contains up-to-date photographs of the basin and real-time graphs comparing current lake levels to the predicted peak. They designed the website to be useful to both their partners and the public, a “one stop shop” where anyone in Juneau (or really, the world) can monitor upcoming Suicide Basin glacial outburst floods each summer. 

The National Weather Service uses the website to issue flood watches and warnings in the area, supplementing their existing rain-based flood forecasting systems. 

“Our forecasters use the website daily to monitor the situation up in Suicide Basin,” says Jacobs. “We have people here 24 hours a day [during the flooding season], so whenever we get new images, we are looking to see if there's anything that we should act on.” 


Push A Button, Good to Go 

A home nestled between tall pine trees is surrounded by grey floodwaters reaching several feet up the first story walls.
Suicide Basin glacial outburst floods sometimes inundate a nearby neighborhood in Juneau, Alaska, requiring evacuations and causing property damage to homes and vehicles.

The forecasting website has also been a game-changer for the Juneau emergency management community.  

“With the first event, it wasn’t until the middle of the flood that we knew what w

as happening,” says Mattice. “Now, we typically have 24 to 36 hours of advanced warning and pretty close [estimates for] how high the water is going to be. While the first three or four years were chaotic every time the river would flood, now it's just like, push a button, make seven phone calls, everybody goes to work, and we know what we're doing.” 

“Our flood modeling experts have done an amazing job of working together and rounding out those numbers and really understanding their models.” 

The monitoring system facilitates a highly coordinated flood response. Once it’s go-time, Juneau Emergency Management Program officers work with the U.S. Forest Service to close campgrounds and trails around the Mendenhall Glacier and relocate displaced campers. They notify homeowners in the potential flood zones, who in turn activate neighborhood sandbagging communities. They put up signs in businesses and roadways, directing people away from the river. 

For their part, Juneau residents and homeowners keep close tabs on the website, anticipating the next flood instead of waiting for sudden evacuation notices. 

“I went to a barbecue on the beach one year, the year we had the biggest flood ever, and there were probably eight people there on their phones watching [the Suicide Basin flood forecasting site], refreshing the page, talking about, ‘Did you see how much water's in Suicide Basin?’” Hood recalls. “When it gets close to the flood, it is one of the most viewed pages on the Juneau National Weather Service site.” 

“That's an amazingly cool thing.” 


An Icefield Community 

But the Juneau community doesn’t just view the floods as a natural disaster. They are also a spectacle, an event, one more thing that makes their community special. 

“In Juneau, people are just fascinated by seeing this happen at their glacier,” Hood says. “There'll be hundreds of people that will come out on the bridge and to the Mendenhall Glacier Visitor Center just to watch the flood. There can be more water flowing down the Mendenhall River than there is in the Colorado River through the Grand Canyon when the outburst flood is big. It's really impressive to watch.” 

“Everybody comes rushing out,” says Laurie Craig, recalling her time as Lead Naturalist at the Mendenhall Glacier Visitor Center. “It doesn't document well in photographs, it's something you have to experience.”  

The floods are a tangible connection to the ice that defines Alaska living. But they are also a reminder of what the community is losing as climate change causes the glaciers to shrink more and more every year. 

“We are diminished by losing the ice,” says Craig. “It's like measuring your life and seeing yourself get older, as the glacier gets smaller and is dying.” 

“There's a sense of grief, there's a sense of mourning.” 

Eventually, the Mendenhall Glacier will become too small to dam Suicide Basin and the community will no longer experience glacial outburst floods. Even today, the glacier has thinned enough that the floods are smaller than they were ten years ago. Climate change has already begun taking away the phenomenon it created in the first place.  

But until then, the research team is determined to learn as much as they can. 

“We happen to be in a time and place where we have this right now, but decades from now people might look back and say, ‘I don't even remember that, that doesn't happen anymore’” Hood says. “So, it's crucial to study it while we have the opportunity. Then we can take that to other places because this is happening all over Alaska. And it's likely to happen more and more as the climate warms.” 

“It's not just something that we're seeing in Alaska,” Gray agrees. “This has emerged on the international radar as something that we really need to be paying attention to, as a consequence of climate change.” 

This research was funded by the Alaska CASC project "Improving Forecasts of Glacier Outburst Flood Events". To learn more about the project, check out this interactive ArcGIS Storymap and this video created by the Alaska CASC showcasing the work. 

Get Our News

These items are in the RSS feed format (Really Simple Syndication) based on categories such as topics, locations, and more. You can install and RSS reader browser extension, software, or use a third-party service to receive immediate news updates depending on the feed that you have added. If you click the feed links below, they may look strange because they are simply XML code. An RSS reader can easily read this code and push out a notification to you when something new is posted to our site.