New Theory Reveals Arctic Riverbeds Erode Faster During Thaw

Arctic erosion rates can spike up to 10 times faster during initial seasonal thaws than unfrozen ground, according to a new scientific theory developed by researchers at Simon Fraser University and the University of British Columbia. Earth scientists previously believed that ice in riverbeds acted as a sort of glue, holding the landscape together and slowing down erosion.

The findings challenge conventional understandings of how cold-region rivers behave. According to Jonas Eschenfelder, a PhD candidate in SFU’s School of Environmental Science, the research team originally expected opposite results when they set out to model river erosion in Canada’s High Arctic.

We literally expected to see the opposite of what we ended up seeing. We re-ran the experiments a whole bunch of times until my supervisor actually believed the results.

Jonas Eschenfelder, Simon Fraser University

Challenging Conventional Assumptions About Arctic Riverbeds

For years, researchers maintained that frozen ground in river systems acted as a cohesive binder, holding particulate matter together and resisting hydraulic forces. However, observations made by SFU assistant professor Shawn Chartrand during a 2019 visit to the Arctic prompted a reevaluation of those assumptions amid rapid climate warming.

Chartrand noted that initial experimental results ran counter to basic science. According to Chartrand, after observing the unexpected outcomes, he emailed colleagues who also doubted the findings before running a second experiment that yielded the exact same outcome.

We saw the results, we looked at ourselves, we said, ‘this can’t be correct.’ I emailed some colleagues. They didn’t believe me. We ran a second experiment. Same outcome.

Shawn Chartrand, Simon Fraser University

Simulating Arctic Thaws Using Laboratory Flume Experiments

To investigate the mechanics behind the phenomenon, Eschenfelder designed a laboratory simulation in an underground facility beneath the Earth Science building at the University of British Columbia during the summer of 2024. The setup utilized a physical flume channel filled with glass beads to represent riverbed sediment, alongside water flow to simulate river dynamics and thermal thawing.

By adjusting water temperatures across different test runs, the research team modeled both temperate and Arctic river conditions. Dislodged glass beads flowed out of the channel where they were counted to measure erosion rates. The experiments revealed that frozen riverbeds subject to initial thawing experienced erosion rates up to 10 times higher than unfrozen counterparts, while also forming distinct steps and depositional pools.

Mechanics of Rapid Thaw Erosion

Once initial skepticism faded, the research team identified the physical processes driving the rapid loss of material. In temperate, unfrozen riverbeds, spaces between small sand and gravel particles allow water to flow through, which limits erosion under normal flow conditions.

In contrast, a completely frozen riverbed blocks internal water infiltration because solid ice fills the subsurface pores. Consequently, all river water remains at the surface and flows faster. As seasonal warming thaws the top layer of ice, surface water injects downward until it strikes the underlying frozen barrier, redirecting the flow upward and loosening bed particles into the fast-moving current.