Seasonality of rockfall triggers and conditioning factors interpreted from a lidar-derived rockfall database

Abstract

Relationships between rockfall and environmental factors have been the focus of considerable research over the last several decades. Many prior studies have not quantified rockfall volume due to challenges in volume estimation without the use of modern remote sensing methods, and the role of longer-term conditioning factors on rockfall activity is often not considered. As part of a broader effort to evaluate rockfall hazard for slopes along the heavily trafficked Interstate-70 corridor in Colorado, this study takes advantage of a high temporal resolution lidar-derived rockfall database consisting of over five years' worth of rockfall data at a particular cut slope to evaluate the relationship between rockfall activity and environmental factors. The combination of monitoring duration and spatiotemporal monitoring resolution used allows for evaluation of both triggering and conditioning factors. Correlations are evaluated between rockfall metrics and weather metrics at a seasonal scale as well as the scale of individual monitoring intervals. Based on the results, it is interpreted that surficial rock material is weakened each Winter by freezing processes, large amounts of rockfall occur in the Spring as a result of the slope thawing out, elevated rockfall activity continues over the Summer as surficial rocks destabilized by freezing processes in the previous Winter are fully dislodged, and rockfall activity significantly reduces in the Fall due to the number of unstable blocks available to fall being significantly reduced. From comparison with the literature, we conclude this cycle is relatively consistent with rockfall trends observed in alpine environments, while more temperate regions exhibit notably different trends in rockfall seasonality.