Published In

Journal of Geophysical Research: Earth Surface

Document Type

Article

Publication Date

1-2025

Subjects

Climatic changes, Permafrost, Geology -- Holocene

Abstract

Rapid, transient, landscape‐scale changes associated with deglaciation can condition slopes for failure and trigger bedrock landslides. However, the mechanisms leading to paleo rock slope failures following the last glacial period are challenging to infer because observations of how both landsliding and potential driving factors were distributed in space and time are limited. Here, we map and analyze the spatiotemporal pattern of 676 post‐glacial bedrock landslides around Eyjafjörður in north‐central Iceland using 2‐m resolution digital elevation data generated from optical stereo satellite imagery. Frequency‐ratio analysis demonstrates that after controlling for slope, landslides are most overrepresented within 2.6 km horizontal distances from surface projections of major Tertiary bedrock structures and at land surface elevations within 300 m of a modeled lower limit to permafrost. Surface roughness analysis of landslide deposits indicates that peak landslide frequency of at least 0.2 landslides yr􀀀 1 in the 5,579 km2 study area lagged deglaciation by several thousand years. This timing aligns well with that of rapid permafrost degradation from the Younger Dryas (12.9–11.7 cal ky BP) through the Holocene Thermal Maximum (∼10–7 cal ky BP). Landslide frequency has averaged about 0.014 landslides yr􀀀 1 since the Holocene Thermal Maximum when the climate has generally been cooler and permafrost has been more extensive. However, present day warming is likely to reduce permafrost extent and increase the potential for bedrock landslides in north‐central Iceland, as has already been observed for several recent shallower landslides in regolith.

Rights

© 2025. The Author(s). This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial‐NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made.

https://creativecommons.org/licenses/by-nc-nd/4.0/

Description

Plain Language Summary
As glaciers recede and expose mountain slopes that were previously covered by ice, dramatic changes in the forces acting on those slopes occur. Those changing forces can trigger large bedrock landslides, which are potentially hazardous to humans and also play a role in sculpting landscapes over longer geologic time scales. Although changing conditions and their connection to landslides can be monitored in real‐time at some locations, it is challenging to determine the mechanisms responsible for generating prehistoric landslides. In this study, we mapped and analyzed 676 landslides in north‐central Iceland that occurred after the Icelandic Ice Sheet retreated and exposed the underlying land surface beginning about 13,000 years ago. Landslides did not occur randomly across the landscape; they instead clustered near zones of weaker rocks and near the margins of high elevation permafrost zones. In addition, about 90% of the landslides likely occurred several thousand years after the ice sheet retreated, during a time in which permafrost was rapidly degrading under warmer temperatures. These results imply that thawing permafrost was an important trigger of large landslides in the past and may become an important trigger again as ongoing warming and permafrost degradation in Iceland continues.

DOI

10.1029/2024JF007933

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