Thawing permafrost and rusting rivers update
The following article appeared in the IARC 2025 Annual Report (Year in Review) publication. This research also contributed to a recent (in press) article in the journal Communications Earth & Environment, an open-access journal from the Nature Portfolio.
Dial, R.J., Hanna, C.T., Sullivan, P.F. et al. Permafrost thaw controls iron flux from wetlands and sulfide-bearing rocks to Arctic rivers and streams. Commun Earth Environ (2026). https://doi.org/10.1038/s43247-026-03450-x
Thawing permafrost and rusting rivers: Understanding the changes in the Arctic
by Diego Noreña
Imagine a creek cutting through the Arctic tundra in Northwest Alaska. You’d probably picture water that is clear, icy, maybe even turquoise. The reality is that in many parts of the region streams are turning a “shocking vibrant orange or rust red.”
That’s how IARC researcher Go Iwahana describes the emerging “rusting river” phenomenon. Rusting rivers are one of the clearest visual signs of rapid permafrost change in Arctic Alaska. Since 2018, streams in the Ikalukrok Creek watershed near the Red Dog Mine have begun showing signs of discoloration and elevated amounts of total dissolved solids.
Understanding those mechanisms requires looking at the water, the material composition, ice content and history of the permafrost. Iwahana and colleagues set out to understand why rusting rivers were appearing so suddenly and in such remote areas. Climate data revealed that 2018 and 2019 brought exceptionally warm summers, triggering a rapid increase in permafrost temperatures. Those warm years led to the formation of taliks, unfrozen areas within permafrost, and the deepening of the active layer.
Masters student Caitlynn Hanna used the GIPL2 permafrost model to simulate how ground temperatures and active layer thickness have changed over time. Her work showed that increased snow accumulation in the region has further insulated the ground, reinforcing warming trends. As the active layer deepens, summer rainwater can penetrate deeper than in the past.
Crucially, Iwahana noted that “the increase in permafrost temperature happened before the peak of the stream chemistry change.” That timing helped demonstrate a tight connection between permafrost warming and shifts in stream chemistry. “If the thaw depths increase, the summer rainwater can infiltrate deeper down and reach acidic bedrocks,” Iwahana explained. Once that water interacts with mineral-rich or sulfur-bearing layers, the dissolved materials flow into downstream waters, creating the rusty
coloration and chemical peaks observed in monitoring data.
To complete this picture, the team combined remote sensing, modeling and fieldwork. High-resolution PlanetScope imagery mapped the expanding stretches of rust colored streams. InSAR analysis using images from satellites ALOS 2 and Sentinel-1 revealed up to 20 centimeters of ground subsidence in 2018-2019 in places, showing evidence of thawing ice-rich permafrost beneath the surface.
Permafrost cores added another layer of insight. Samples from the region contained yellow and orange-stained ground ice. “That ice was formed thousands of years ago,” Iwahana said. “And the color is exactly the same as what we see in the rusting river.” This suggests that similar chemical processes occurred naturally in the past, though today’s warming is accelerating them.
The project demonstrated that warming air temperatures, deeper seasonal thaw, talik formation, and mineral leaching are all interconnected. By tracing how these processes unfold, and in what order, the research provides a foundation for anticipating future events.
While permafrost thaw cannot be stopped, Iwahana emphasizes that knowledge can help communities prepare. “We cannot stop global warming or permafrost degradation,” he said. “But knowing what is included in permafrost and the timing of the temperature increases, we can be proactive and react appropriately.”
Permafrost thaw releases minerals, turning this creek orange.