Evaluating rockfall frequency from natural slopes (multiple methods)

Understanding of rockfall frequency-magnitude relationships is important for managing rockfall hazards, but characterizing these relationships is a challenging problem due to limited data, limited access, and the difficulty of accurately dating historic rockfalls. Developing frequency-magnitude relationships can be particularly difficult for natural rock slopes, which can still present significant hazards, but where data is often sparser due to greater distance from roads and buildings. This talk will provide an overview of the topic of rockfall frequency measurement by briefly discussing the relevant literature and presenting examples from the application of two different methods to the same study sites. The literature review will present a summary of methods previously applied to measuring rockfall frequency, including advantages and disadvantages of various approaches. The two case studies will come from original research in Glenwood Canyon, CO, an area where natural slopes present significant rockfall hazard to Interstate 70, but where previous knowledge of rockfall behavior consists mainly of the anecdotal insights gained by highway management personnel, without the benefit of systematic study. The first case study was conducted using lichenometry, and the second is based on an ongoing drone-based monitoring campaign. Comparisons between the results for the two methods will be made, and implications of these results for rockfall behavior in Glenwood Canyon will be discussed.

Graber A (2021). Evaluating rockfall frequency from natural slopes at multiple timescales using multiple methods; Examples from Glenwood Canyon, CO. USGS Landslide Hazards Program Seminar Series, 20 October 2021.