VARIATIONS IN POPULATION EXPOSURE AND SENSITIVITY TO LAHAR HAZARDS FROM MOUNT RAINIER, WASHINGTON

Although much has been done to understand, quantify, and delineate volcanic hazards, there are fewer efforts to assess societal vulnerability to these hazards, particularly demographic differences in exposed populations or spatial variations in exposure to regional hazards. To better understand population diversity in volcanic hazard zones, we assess the number and types of people in a single type of hazard zone (lahars) for 27 communities downstream of Mount Rainier, Washington (USA). Population exposure to potential lahar inundation varies considerably – some communities have large numbers but low percentages of people in hazard zones whereas others have fewer people that comprise the majority of a community. We calculate composite indices that combine the number and percentage of people and assets in lahar-prone areas to help emergency managers understand spatial variations in community exposure. We find that communities vary in the primary category of individuals in lahar-prone areas – exposed populations are dominated by residents in some communities, employees in others, and tourists can outnumber both of these groups. Risk education and preparedness needs will vary based on who is threatened by future lahars, such as residents, employees, tourists at a public venue, or special-needs populations at a dependent-care facility. Emergency managers must first understand who they are trying to prepare before they can expect people to take protective measures after recognizing natural cues or receiving an official lahar warning.