SOCIETAL GEOHAZARD RISK AS A CONVERGENCE OF GEOLOGIC AND ANTHROPOGENIC HISTORIES

Two common problems impede understanding of risk and thus limit risk reduction. First, nearly all views of risk focus on only some of its four composite factors: hazard, exposure, vulnerability and coping capacity. The focus of natural science is on hazard and exposure, whereas social science focuses on vulnerability and coping capacity. The strengths of both approaches are important in understanding and analyzing societal geohazard risk, but the two are rarely integrated or unified. Second, most analyses of risk consider only the most proximate causes, and therefore the four risk factors may be misidentified or oversimplified, while ultimate root causes go unrecognized. Limited understanding of risk due to these two factors has three repercussions: reduced understanding of risk causation; reduced recognition of the array of impacts through which risk is revealed; and reduced potential for risk reduction. One approach to increasing understanding of risk is to consider two parallel histories determining risk. The geologic history of a location, spanning up to billions of year, plays a major role in determining hazard and exposure. The anthropogenic history of a location, spanning up to thousands of year, plays a major role in determining vulnerability and coping capacity. Each history can influence all four risk factors. Consideration of geologic and anthropogenic histories as determinants of societal geohazard risk utilizes fields in both natural science, including Quaternary geology, engineering geology, geomorphology, tectonics and climatology, and social science, including human geography and historical analysis. Combined research in several of these fields serves as the basis for an innovative conceptual model of risk that considers ultimate causes in addition to proximate causes. This approach is explored through a consideration of societal landslide risk in the Bolivian Andes, with specific attention to two contrasting locations: the city of La Paz and the pueblo of Yocarhuaya. Interaction of a wide array of natural and social conditions rooted in the geologic and anthropogenic past determines the high diversity and low predictability of landslides and their impacts in the region.