High Drama When the River Runs Again

by Beth Grassi

In late April 2014, I stood on a bridge in Fairbanks watching the Chena River waking up under my feet. Flat chunks of ice bumped and bobbed down the river, some a thin, translucent gray, others rafts of white several inches thick. Ice floes and slush hissed through the rush of river water. It felt like standing on the prow of a ship, pushing through to spring. “Spring breakup” may sound like a sitcom episode, but in Alaska it’s a landscape-size drama.

Most of Alaska’s rivers freeze over in winter, with ice up to several feet thick. When the rivers finally break free, usually in April and May (or even June in the Arctic), ice floats downstream. Sometimes ice jams—jumbles of ice floes—dam up a river. Large ice jams can cause dangerous flooding. 

Breakup plays out differently each year on each river, a complicated dialog between temperature, snowpack, wind, rain, river features, and river tributaries. Fall freeze-up conditions, midwinter thaws, and following refreezes also play a part. But not all parts play an equal role. “The weather in late March and April really determines the character of the ice melting out,” says Rick Thoman, a climate specialist at the University of Alaska Fairbanks. He served as a National Weather Service forecaster in Alaska for 25 years. “Snow runoff is a secondary factor to breakup.” 

The National Weather Service’s Alaska-Pacific River Forecast Center in Anchorage generates water forecasts. The center’s team explains there is a spectrum of how river ice departs, from thermal to mechanical breakups. 

In early May 2009, the Yukon River began to break apart near the Alaska-Canada border. While open water was seen near the small Alaskan community of Eagle, an ice dam formed a few miles downriver, causing a backup of massive ice chunks that were forced over a retaining wall and into town. Numerous buildings were destroyed. This photo shows two gas pumps (a third was missing) left standing in front of Eagle Trading after the event.

A thermal breakup, or “mush out,” is when the ice melts in place. When April and May are warm and sunny, the ice and snow melt gradually. Snowmelt doesn’t raise river levels quickly, so ice stays in place longer as it melts. The weak ice finally breaks into smaller, more fragile pieces, with less chance of hazardous ice jams.

 Mechanical, or dynamic, breakups occur when April and May are cold and overcast with a sudden switch to warm weather. River ice remains thick and strong. Water levels rise from quickly melting snow, breaking ice suddenly or lifting it free in large sheets. Massive ice blocks surge downstream, and if they catch on anything, such as a sandbar or sharp bend in the river, they pile up into an ice jam. Water backs up, flooding upstream areas until the water forces the ice loose again. The breakup front is the boundary between broken ice upstream and intact ice downstream. The breakup front may pile up and release multiple times as the ice heads downstream. 

This graph shows a trend toward earlier breakup at three locations: the town of Nenana on the Tanana River, Dawson City on the Yukon River, and Bethel on the Kuskokwim River.


Ice jam flooding can be extremely dangerous for nearby communities. “The water can rise feet in minutes, and when it releases, it can be just as fast,” says Thoman. Some communities have stretches of river prone to ice jams, such as Bishop Rock downstream from Galena on the Yukon River, which generated a major flood in 2013. “Some of these locations cause jams each year or even several times through breakup,” says the River Forecast Center. On the Tanana River, Manley Hot Springs experienced damaging flooding in 2022. On the Kuskokwim River, Napaimute faced major flooding in 2020.  

Ice Watchers

Monitoring ice on Alaska’s rivers requires combining everything from community observers to cameras on riverbanks to satellite imagery. 

“To us the ice is a living thing, like other parts of our environment,” says Mark Leary, Director of Operations for the Native Village of Napaimute. “We watch it being born, growing up and maturing all winter, then as it gets older, we watch it deteriorate and die in the spring. The ice is changing every day when we are out there on it.” On the Kuskokwim River, Leary and a team from Napaimute lead the establishment of the seasonal Kuskokwim ice road.

People travel by car and truck along the 200-mile road to buy supplies, attend medical appointments, and visit between communities. “We monitor continuously and eventually close the road and remove all the markers. With the strength of the sun in April it starts to melt. Anything dark—sand, sticks, etc.—melt faster into the ice. It gets bumpy, so people stop traveling long before it’s dangerous and they could fall through,” says Leary. Blending traditional knowledge with technology, such as ice radar, they are developing a mobile app to share ice depth and safety information.

Swift water tumbles over ice on Globe Creek along the Elliott Highway on April 19, 2020, flooding the surrounding forest.

The National Weather Service River Watch program partners with local people who live near, travel on, or fly over rivers to report ice conditions. The River Forecast Center and the State of Alaska Emergency Operations Center fly daily aerial surveys along the Kuskokwim and Yukon rivers for two to three weeks in late April. “VHF radio reports are given from the air to the villages as we fly over about ice and river conditions…Often we invite local community members to accompany us on these flights,” says the River Forecast Center. 

In 2019, a new UAF project called Fresh Eyes on Ice started, partnering with teachers and students in schools across Alaska to monitor ice. Students measure ice thickness and snow depth once a month (most work on lakes, some on rivers). Students in Eagle monitor the Yukon River, and students in Sleetmute monitor the Kuskokwim. In 2022, the project gave about half the involved schools small drones to take aerial photos. Students in Sleetmute and McGrath used their drones to document ice jam flooding in May 2022. Student data and photos go into the National Weather Service database.

Spring Breakup is a Guessing Game

Ice classic contests started as local entertainment. The game is simple. A community sets a large tripod out on the frozen river. When the ice begins to float away in the spring, it pulls a cord that stops a clock. Participants buy tickets to make guesses of the exact time and date the clock will stop. The closest guess to the official tripod time wins. In addition to the winner’s prize, money from these events goes to support nonprofits, charities, and scholarships. 

Three long-running ice classic contests still draw participants from around the world. The Nenana Ice Classic on the Tanana River began in 1917 when engineers surveying for the Alaska Railroad started a betting pool. The Kuskokwim River Ice Classic in Bethel started in its current form in the 1980s. The Yukon River Ice Pool in Dawson City, Canada, started in 1896. There was a Chena River contest that started in 1903 in Fairbanks, but a dike built in the 1940s and later a power plant built on Fort Wainwright that releases warm water into the Chena affected the breakup pattern enough that the contest faded out in the 1970s. 


Online breakups in the dating world are a no-no, but tracking Alaskan river breakups each spring online is a definite yes. Here are some resources to pen into your little black book—er, um, to bookmark.


All three contests have links to live webcams. 
Nenana Ice Classic: nenanaakiceclassic.com
Kuskokwim “Kusko” Ice Classic: iceclassic.org
Yukon River Ice Classic: dawsoncity.ca/yukon-river-ice-pool

AlaskaN River Breakup Resources

Alaska-Pacific River Forecast Center
Breakup Map: weather.gov/aprfc/breakupMap 
River Notes: weather.gov/aprfc/riverNotes 
River Watch: weather.gov/aprfc/riverWatchProgram 

UAF Fresh Eyes on Ice: fresheyesonice.org

Kuskokwim River Ice and Road Conditions Facebook group: facebook.com/groups/433512193777148

The timing of spring breakup on Alaska’s rivers is changing. Over the course of a century, spring breakup dates on the Tanana River at Nenana and the Yukon River at Dawson City have shifted about a week earlier. Surprisingly, the best long-term records in Alaska are ice classic contests. “Because money was riding on it, they were careful to always do it the same. They still do it the same way now,” Thoman says. It may not be scientific, but for long-term studies, “it’s the consistency that matters the most.” 

As the sunlight stretches longer this spring, whether it’s walking out your door to the river or joining in an ice classic contest from afar, take some time to marvel at the ice drama of spring breakup in Alaska.   

Beth Grassi is a freelance writer fascinated by Alaska’s natural history. She illustrated several children’s books and is an avid birder. She calls Fairbanks home.

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