ASSESSING RISK FROM ROCKFALL AND PLACING RISK IN SOCIETAL CONTEXT

It is National Park Service policy to devise effective strategies to identify geologic hazards and to strive to understand them and minimize risk, or the hazard’s potential impact on visitors, staff, and developed areas. Rockfall is a hazard that can potentially affect a large number of National Park Service managed units. Recent efforts to assess rockfall risk at Chaco Culture National Historical Park and Dinosaur National Monument have used a quantitative risk estimation equation to try to place risk to individuals and visitor populations in a societal context. The risk equation estimates risk in terms of the annual probability of loss of life has been used in risk management in Australia and for assessing life-safety risk from rockfall during the aftershock sequence of the 2010/11 Canterbury New Zealand earthquakes. The strength of using a quantitative estimate is that risk from an identified hazard can be placed in context with other societal risks such as driving a car or the risk of death in the broader population from an accidental fall. Potential drawbacks with using a risk equation are the number of factors that require an estimate, often without strong corroborating data, and uncertainty about what the highest tolerable imposed risk should be for any given hazard.