Down in the Slumps: Tracing Erosion Cycles in Arctic Permafrost

Source: Journal of Geophysical Research: Earth Surface

In the Arctic, landslide-like features known as mega retrogressive thaw slumps are threatening infrastructure, altering regional biogeochemistry, and emitting carbon.

Sometimes eroding more than 1 million cubic meters (about the volume of 400 Olympic-sized swimming pools) of sediment and ice during their lifetime, these slumps are erosional landforms that occur when permafrost thaws. They are common on hillsides and along shorelines.

The basic mechanisms of slumps are well described in the permafrost literature. But less well understood is what causes them to form, especially in the same locations where others occurred previously—a phenomenon known as polycyclicity.

Krautblatter et al. used electrical resistivity tomography (ERT) and ground-penetrating radar (GPR) to study how slumps form and then reactivate after going dormant. The research took place on Herschel Island in Yukon, Canada, a global hot spot for slumps. As many as 90% of active slumps in the Canadian Arctic are polycyclic. Though GPR and ERT are common geophysical reconnaissance tools, this study is one of the first times they were used to reveal the inner structure of polycyclic slumps.

The surveys uncovered several mechanisms driving slump evolution. The ERT survey showed that intruding seawater at the farthest-reaching edge of a slump floor (also known as the toe) can destabilize permafrost and initiate a new slump. As slumps retreat, the ground surface cover changes and the underlying permafrost warms. This warming then extends tens of meters into the ground, where it can persist for up to 300 years, priming the ground material to develop into yet another slump in the future.

In addition, once slumps are reactivated, mudslides develop and narrow ravines can form, removing organic layers and transporting large quantities of sediment and organic matter to the shoreline. This warms underlying permafrost and continues the cycle.

Using the survey data, the authors developed a classification scheme to characterize the stages of polycyclicity, charting the evolution from undisturbed tundra to slumps retreating beyond their historic limits. Not all slumps follow this precise progression, but the framework offers a common language for comparing those of similar size or behavior. The insights offer an improved understanding of temporal and spatial patterns of this unique Arctic form of erosion. (Journal of Geophysical Research: Earth Surface, https://doi.org/10.1029/2023JF007556, 2024)

—Aaron Sidder, Science Writer

Citation: Sidder, A. (2024), Down in the slumps: Tracing erosion cycles in Arctic permafrost, Eos, 105, https://doi.org/10.1029/2024EO240473. Published on 21 October 2024.

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