Comparison of monitoring data with paleo-slip rates: Cosmogenic nuclide dating detects acceleration of a rockslide

摘要

Instrumental monitoring of displacement rates of slow-moving rockslides is limited to an insufficient length of the pre-catastrophic failure deformation time. Prehistorical slip rates need to be considered to provide context for monitoring data in relation to the length of the failure process. Cosmogenic Be-10 exposure ages (n = 10) on the backscarp of the Gamanjunni-3 rockslide (northern Norway) are between 5.3 +/- 0.5 ka and 1.2 +/- 0.1 ka. These ages were adjusted for prefailure nuclide production at depth based on the Be-10 concentration in quartz from a stable horizontal bedrock surface above the rockslide. Displacement initiated between 6.6 and 4.3 ka with a relatively fast or instantaneous displacement rate that decelerated a few hundred years after initiation. Slide initiation coincided with the end of the Holocene thermal optimum in northern Norway. The age-height relationship on the backscarp yields an average paleo-slip rate of 28 (-5/+7) mm/yr. This is significantly slower than present-day rates of 54 mm/yr. However, during slide initiation, slip rates were faster than present-day rates. Considering its location within the modern permafrost zone and the observations from instrumental and Holocene displacement rates, we suggest that future global climate changes will influence the Gamanjunni-3 block slip rate.