The USGS Volcano Hazards Program develops, updates, and disseminates short-and long-term volcano hazard assessments to inform decisions that can mitigate potential adverse consequences and save lives and property. Detailed knowledge of a volcano's past eruptions and a broad understanding of volcano activity at similar types of volcanoes provide the scientific rationale for assessing its likely long-term future activity. New volcanic unrest and significant changes to an ongoing eruption may warrant revised short-term hazard assessments, including analysis of several possible scenarios for a volcano's behavior.
Records of past eruptions and the distribution of volcanic deposits are obtained through detailed geologic field investigations, accurate dating of eruptive products, and physical and chemical analysis of the material. The geologic evidence provides the locations, magnitudes, styles, and frequencies of previous volcanic activity. These data are integrated with high-resolution topographic mapping of the landscape (digital elevation models) and analyzed using Geographic Information Systems (GIS). Numerical process models of realistic hazardous phenomena are combined with the GIS analysis to produce different types of hazard zonation maps, which may include probabilistic estimates of how often and at what magnitude events will recur. Regional and volcano-specific hazard assessments are updated as needed when new data are acquired or scientific understanding improves.
Assessments serve as critical inputs for public policy on land-use planning, emergency plans, and preparedness activities. Assessments also provide a starting point to develop coordinated interagency response plans, which provide a map for how multiple government agencies should interact during periods of volcanic unrest.