Chapter 15 - Rockfall hazard and risk

Abstract

Rockfall is one of the most frequent and damaging types of mass movement, and in this chapter, we consider aspects of rockfall hazard and vulnerability that lead to risk. We focus on the current ability to assess rockfall risk, drawing on recent research utilising extensive inventories and datasets on rockfall occurrence and impact. We begin by considering two aspects of rockfall hazard: forecasting rockfall hazard from historical observations and investigating the uncertainties associated with the temporal resolution of rockfall observations. We then consider the exposure and vulnerability of property and people to rockfall hazards, which are key determinants of rockfall risk and loss. To illustrate this, we draw upon two case studies where unique data on rockfall occurrence and impact have been collated, providing insight into the hazard and risk that rockfalls pose. Our first is from coastal rock cliffs in North Yorkshire, United Kingdom, and our second is from rock slopes that experienced shaking in the 2011 Christchurch earthquakes, New Zealand. Many research studies of rockfall arise from a need to manage rockfall risks, providing a wealth of information on assessing and mitigating rockfall hazard, which we signpost throughout to supplement these case studies. The case studies show that (i) the temporal resolution of rockfall surveys tend to dominate our interpretation of rockfall frequency–magnitude distributions and hence hazard, whereas these should be based on survey resolutions and durations of sufficient temporal resolution and duration to capture all plausible event magnitudes and (ii) in general, rockfall risk analyses commonly adopt overly simplistic exposure and vulnerability assumptions, rather than more nuanced event tree approaches that link hazard intensity to determinants of exposure such as time of day, setting and cognitive awareness.