Thawing Arctic Riverbeds Erode Up to 10 Times Faster Than Unfrozen Ground, Study Finds

Researchers at Simon Fraser University have found that thawing riverbeds in Canada's High Arctic can erode up to 10 times faster than unfrozen ground during the initial thaw, overturning the long-held assumption that ice in the ground acts like glue that slows erosion. The findings, based on laboratory experiments, come as Arctic landscapes warm about four times faster than the rest of the globe.

"We literally expected to see the opposite of what we ended up seeing," said Jonas Eschenfelder, a PhD candidate in SFU's School of Environmental Science, who built the experiment with his supervisor, assistant professor Shawn Chartrand. To test how frozen ground erodes compared with unfrozen ground, the team built a flume, a lab channel filled with glass beads representing a riverbed, and ran water over it at different temperatures, counting beads that were picked up and washed out to calculate erosion rates.

The team found that in early summer, when ice is still melting in the ground, surface water that seeps into a partly thawed riverbed hits a layer of remaining ice and gets redirected upward, loosening sediment from below and carrying it downstream. That process, absent in fully unfrozen or fully frozen ground, produced erosion rates up to 10 times higher than in unfrozen rivers, along with small steps and pools that formed unevenly along the riverbed.

"The Arctic is warming about four times faster than the rest of the globe. And with it, landscapes — polar deserts that have been largely unchanged for more than 10,000 years — are waking up and beginning to form new river systems," Eschenfelder said, adding that new rivers have formed within tens of years, faster than erosion typically proceeds even in temperate landscapes.