Permafrost and Structural Controls on Holocene Bedrock Landslide Occurrence Around Eyjafjörður, North-Central Iceland

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.