NVEWS THREAT ASSESSMENT REVISITED: FINE-SCALE POPULATION, INFRASTRUCTURE, AND FACILITY METRICS NEAR ACTIVE VOLCANOES

The national volcanic threat assessment, developed in support of the USGS National Volcano Early Warning System (NVEWS) framework, provides a relative ranking of threats posed by all U.S. volcanoes. The threat assessment will help to prioritize monitoring strategies, mitigation plans, and hazards assessments throughout the U.S. The numerical threat rating assigned to each of the 169 U.S. volcanoes is based, in part, on population and facilities potentially exposed to hazards within a uniform distance of the volcanic center.

We present a revised exposure assessment of volcanoes in the conterminous U.S. based on analyses of fine-scale population, infrastructure, and facility datasets, in order to better quantify societal exposure to volcanic hazards. We calculated exposure metrics within a standard 30 km exposure radius at each volcano. The 30 km distance is based on historical evidence of hazardous pyroclastic-flow and tephra-fall zones. Where additional exposure zones (i.e., flowage hazards) are mapped, exposure counts within these zones were also quantified. We gathered information about population from census 2000 (block-level units) and LandScan databases and we gathered infrastructure and facility information from various Federal, state, county, and municipal sources. Exposure metrics can be useful aids in promoting knowledge, understanding, and preparedness within communities subject to volcanic hazards.

We also present preliminary dasymetric modeling results of high resolution (sub-census block; 10 m) population counts within 30 km radii of Cascade volcanoes. Dasymetric modeling refines estimates of population counts by using ancillary data as a statistical base that determines the geographic location of people within an areal unit (i.e., census blocks). Relevant ancillary datasets include classified land cover grids, slope gradients, and land use coverages. The end result is a high-resolution, residential-population distribution model that addresses the inherent heterogeneity of populations within arbitrary administrative census units. This result leads to an improved estimation of populations potentially exposed to volcanic hazards.