A team of researchers, including two professors at the University of Alaska Southeast, were recently awarded a nearly $1 million grant from the National Science Foundation for a project that will help to better map and predict the Suicide Basin glacial lake outburst flood that has devastated Juneau’s Mendenhall Valley over the past two years. Long term, the project opens up the door to identifying and predicting other outburst flood risk zones across Alaska.
The project is being led by Dr. Jason Amundson of UAS in partnership with researchers from University of Alaska Fairbanks and Carnegie Mellon University. At UAS, Dr. Amundson is joined by Dr. Eran Hood, the UAS Natural Sciences Department Chair and a professor of environmental science.
“We have 14 years of research on this flood, but obviously the last two years it was a lot larger and more impactful,” said Dr. Hood, who began his work with Suicide Basin in 2011 after the first associated outburst flood occurred.
The last two years have seen back-to-back, record-breaking events. Mendenhall River, usually about six feet deep, reached a crest of 14.97 feet in 2023 during an event that saw two homes entirely destroyed and many other properties damaged by severe erosion. The following year’s 15.99 foot crest rewrote that record during an event that flooded more than 100 homes throughout the Mendenhall Valley.
“We want to beef up our ability to monitor and predict this event on a yearly basis,” said Dr. Hood. “And then we also want to do some modeling work that will allow us to quantify how much it might change in the future, because that will be very useful information in terms of [informing] some of the mitigation strategies that are being proposed.”
Suicide Glacier, a tributary (or side) glacier that used to feed into the Mendenhall Glacier (Tlingit: Áakʼw Tʼáak Sít’), has retreated and left a deep basin in its place between itself and the Mendenhall Glacier. Mendenhall Glacier now acts as a de facto dam to this basin as water accumulates from rainfall, snowmelt and glacial melt. Eventually, since ice is bouyount, enough water fills the basin to float the glacier and escape beneath it. This marks the beginning of the glacial outburst flood.
“It essentially leaks out underneath the glacier, but as water moves it creates friction so once it starts going underneath the glacier, the friction of the moving water melts the drainage channel larger,” said Dr. Hood. “As it progresses, the drain channel gets larger and larger because of the friction, and then the water can start draining very rapidly.”
With a flow of over 33,000 cubic feet of water per second, enough water was flowing during the 2024 peak to fill up 13 Olympic-sized swimming pools per minute. According to estimates from the National Oceanic and Atmospheric Administration, the total volume released was equivalent to nearly 16 billion gallons of water — more than half of Anchorage’s annual water usage, or enough to fill a 10-foot-deep lake spanning nearly eight square miles — all pouring into Mendenhall Lake and River within just a few hours.
To better understand how the whole system is working and the geometry of the basin, the team relies on information collected through technology like drones, time lapse cameras, hydrographs, and stream gauges. Among other pertinent information, drone imagery can offer data about the amount of water being released during a flooding event, how the size of the basin is changing as Mendenhall Glacier thins, and the overall storage capacity of the basin as the volume of ice inside it melts. The researchers also rely on a variety of other tools (some run by the city and organizations like NOAA, the Weather Service, and the U.S. Geological Survey), like a laser rangefinder to measure water level and GPS units to measure ice velocity.
Dr. Amundson says that the first part of this project is to really understand the Mendenhall floods better, to understand how the basin is changing right now, and to gather data that can help them accurately forecast the flood peak. “That has obvious implications for any engineering solution,” he said. “We need to know how much water could come out of the basin and how big of a flood we could get.”
These larger outburst events seen in the past two years aren’t necessarily the new normal, and the researchers say that, in general, the size of any given outburst flood is random. Hood shared that large enough floods to threaten property happened in 2014 and 2016, while the years between saw smaller floods with no damage.
The scale of the flooding is driven by the ever changing shape of the basin. Over the past two years, shifts in the basin’s geometry allowed water to drain to a lower elevation than before — contributing to the unprecedented sizes of the last two floods. For now, it’s not clear whether these larger events represent the new normal or if we’ll see a jump back down to smaller floods.
“Right now … we’re also trying to do some imaging of the bed of the glacier all around that area, and actually of the whole glacier, using a helicopter borne radar. Maybe that will give us some insights into what’s going on,” said Dr. Hood.
The second part of the project is to use the newfound understanding of the mechanics behind Suicide Glacier to do a survey around Alaska and identify other places that could eventually host similar hazards.
“If people had been thinking about this 40 years ago, they might have done the same sort of study of Mendenhall and said, ‘Oh, actually, that looks like it could be a problem in the future,’” said Dr. Amundson. “That’s the sort of thing that we’re trying to do elsewhere.”
Glacial lake outburst flooding events are happening all the time around Alaska. Luckily, the majority occur in locales where no one is living downstream. The team has eyes on the Snow Glacier, which drains into the Snow River and then into the Kenai River, which might have the potential to threaten railroad infrastructure down the line.
The Suicide Basin glacial outburst flood cycle does have a limited lifespan: eventually, Mendenhall Glacier will retreat past the basin. Dr. Amundson hopes this study will offer information about and help create assessment strategies to learn more about other places further upstream and around Alaska that could potentially harbor similar events in the future.
“There’s a little basin on the west side of the [Mendenhall Glacier], a bit farther upstream that may or may not be able to hold water,” Dr. Amundson said. “Then even farther up the glacier, and I’m talking several decades from now, but if Mendenhall Glacier were to retreat really far up the valley, there’s another spot where you could potentially pool water.”
Through their work on this five-year project, Dr. Amundson and Dr. Hood aim to generate the data and mechanical insights needed to improve predictions of glacial lake outburst floods and to guide mitigation efforts and emergency response strategies worldwide.
“For me as a glaciologist, [it’s special] to work on something that has such an impact on my own community,” said Dr. Amundson. “To be here and to see that this thing is impacting people, it’s an interesting thing.”
Rachel Levy is a Juneau-based photojournalist whose work culminates at the intersections of environmental justice, arts and culture, and sustainable tourism. A 2022 graduate of Harvard University's Environmental Policy program, she is also the director of the award-winning documentary "Hidden in Plain Sight" that exposes the labor exploitation and colonial framework burdening Tanzania's safari industry.
