30 April 2025
Northern rivers traditionally freeze over with complete ice cover and thus serve as important travel and transportation corridors. Incomplete freeze‐up in the form of open leads or open‐water zones present hazards to winter travelers, yet knowing where, when, and why these hazards form is uncertain. Using a combination of field measurements and satellite observations, we studied hundreds of open-water zone locations on larger rivers and their tributaries in western Alaska over 6 years. Results show that locations where large persistent open‐water zones form regularly are associated with narrow valleys and sharp meanders. Deeper channels, higher under‐ice flow, and limited groundwater upwelling are also associated with open‐water zone locations. Observations during the early freeze‐up period suggest that upstream ice jams are the primary cause of open‐water zone formation downstream. These ice jams are also hypothesized to enhance turbulence and slow open‐water closure. Future research should focus on how freeze‐up progresses in warmer winters with higher river flows. These study was recently published in the journal Water Resources Research.
Based on early conversations with residents of Bethel, Noatak, and Shageluk about these winter ice hazards, we began investigating the cause of persistent open-water zones on the Kuskokwim and Yukon river and their tributaries based on fieldwork during a late winter snowmachine traverse between McGrath and Galena in 2023. Satellite remote sensing analysis and additional discussions with community members lead us to the finding that freeze-up ice jams set the conditions that allow open-leads to form and persist through the winter. Work is ongoing to study this and other processes in greater detail on the Tanana and Chena rivers near Fairbanks. Stay tuned for more results!