Simon Fraser University researchers modelling High Arctic river erosion got a result so counterintuitive they reran the experiment repeatedly before believing it: frozen ground, in the earliest stage of thaw, erodes faster than ground that was never frozen at all.
Conventional wisdom in geomorphology holds that seasonally frozen ground should erode more slowly than unfrozen ground, since ice adds cohesion to soil and sediment. A team at Simon Fraser University’s School of Environmental Science, led by PhD candidate Jonas Eschenfelder and assistant professor Shawn Chartrand, set out to model river erosion in Canada’s High Arctic and found the opposite: frozen riverbeds can erode up to ten times faster than unfrozen ground during the initial thaw period. “We literally expected to see the opposite of what we ended up seeing,” Eschenfelder said. “We reran the experiments a whole bunch of times until my supervisor actually believed the results.” Chartrand described his own reaction: “We saw the results, we looked at each other, we said, ‘This can’t be correct.’ I emailed some colleagues. They didn’t believe me. We ran a second experiment. Same outcome.”
Using flume experiments — a laboratory channel filled with glass beads standing in for riverbed sediment, with water flow simulating a river at different temperatures — combined with scaling theory and field data, the team found that early-thaw surface water carries heat and momentum into the bed, driving localised subsurface thawing that increases erosion unevenly, producing small stepped terraces and depositional pools rather than uniform erosion. Published in Communications Earth & Environment, the findings help explain a puzzle in Arctic field observations: previously frozen polar-desert landscapes, largely unchanged for over 10,000 years, have in some cases formed entirely new river systems within just decades — far faster than temperate-landscape erosion rates alone would predict.
– Raja Aditya
