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Study and report offer insights into ice conditions

As Alaska’s rivers begin serving as winter roads and trails, a new study from the ������Ƶ helps explain why certain stretches of water never seem to freeze.

Researchers from UAF’s Water and Environmental Research Center, part of the Institute of Northern Engineering, conducted hydraulic modeling and analyzed a decade of satellite data and field measurements. They uncovered how open-water zones — patches of flowing water that persist within otherwise frozen rivers — form and endure near Fairbanks on the Tanana River.

The findings, published in the journal , link the phenomenon to a combination of channel constriction, early-season ice jams and increasing discharge during freeze-up.

“We’ve always known that Alaskans depend on frozen rivers as travel corridors,” said lead author Matthew Scragg, a UAF graduate researcher. “But as freeze-up gets later and flows increase, the physics of where and how ice forms are changing in ways that can impact safety for people traveling over the ice.”

A changing freeze-up pattern

Using Sentinel and Landsat satellite imagery from 2014 to 2023, researchers found that in eight out of 10 years, an open-water zone appeared downstream of a narrow section of the Tanana River after an ice jam formed upstream. Only in years when the river froze downstream first did the open section never appear.

The team combined these observations with under-ice measurements and modeling to reveal that when an upstream ice jam forms, turbulent water beneath the jam prevents ice formation below it, keeping a section of the river open for weeks or even months.

Long-term records show that discharge during the Tanana’s freeze-up season has increased by about 7% per decade since the 1970s, likely due to warming temperatures, permafrost thaw and glacial melt. The study suggests that higher early-winter flows could make persistent open-water zones more common in the future, adding new challenges for travelers.

From research to community impact

The study offers a scientific explanation for the kind of information collected through the statewide Fresh Eyes on Ice network, which involves communities, students and local observers in monitoring river and lake ice conditions. Since 2019, citizen scientists and community monitoring teams have helped collect almost 6,000 photos of river and lake ice conditions to share real-time conditions and aid the Alaska Pacific River Forecast Center’s break-up flooding and hazard forecasting. K-12 students and teachers have recorded hundreds of ice thickness and snow depth measurements on rivers and lakes in their communities.

The project’s combination of satellite science and citizen observations is detailed in a new report, .” The report shares the wonders, hazards and recent changes seen in freshwater ice conditions across Alaska and parts of Canada, highlighting several findings and trends important to Alaskans who depend on frozen rivers for winter access and subsistence activities.

Scientists and educators at the ������Ƶ partner with NASA Global Learning and Observations to Benefit the Environment, the Alaska Pacific River Forecast Center at the National Weather Service, the U.S. Fish and Wildlife Service, Tanana Chiefs Conference and the Alaska Climate Adaptation Science Center to support a variety of ice monitoring methods.

“Open-water zones aren’t just a curiosity; they’re a hazard,” said study and report co-author Chris Arp, an INE hydrologist who leads the Fresh Eyes on Ice project. “By understanding the types of river reaches and freeze-up conditions, we can better predict where they’ll form and help communities avoid dangerous routes. Community photo observations are extremely helpful for informing travelers about these hazards now and in the future.”

To connect with the team or learn how to contribute observations, contact the and ask about .

CONTACT: Chris Arp, 907-474-2783, carp@alaska.edu
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