National Volcanic Threat Layer

There are 161 active volcanoes in the U.S. and its territories. These volcanoes pose differing degrees of risk to people and infrastructure because of differences in their eruptive styles and geographic locations. This layer shows the areas near volcanic vents that could be affected by proximal volcano hazards, including ballistics (airborne rocks from explosions), pyroclastic density currents, lava flows, debris avalanches, lahars (mudflows), and heavy ashfall, as well as areas downstream that could be affected by distal lahars (see the USGS Volcano Hazards Program Glossary for descriptions of these processes: https://www.usgs.gov/glossary/volcano-hazards-program-glossary). These areas are labelled with their corresponding volcano names and threat category as determined by the 2018 U.S. Geological Survey National Volcanic Threat Assessment (https://pubs.usgs.gov/publication/sir20185140, Ewert and others, 2018).

The threat assessment uses a 24-factor hazard and exposure matrix to create a threat ranking for each volcano and places volcanoes into five threat categories: very low, low, moderate, high, and very high. This layer is not a hazards map. It depicts areas that could be threatened directly by volcanic activity in a consistent national format. For local information on hazards for a specific volcano, visit the USGS Volcano Hazards Program website (https://www.usgs.gov/programs/VHP) and use the pulldown menu in the upper right. This layer does not show areas that could be affected by downwind ashfall beyond a maximum of 30 km (19 miles) from volcanic vents. Volcanic ash can impact communities and infrastructure hundreds of km or miles from volcanoes and can interfere with national and international aviation operations. Areas and airspace affected are highly dependent on the size and duration of an eruption, along with wind direction and wind speed. Volcanic threat scores in the 2018 threat assessment account for potential threats to aviation.

An ArcGIS Pro layer file has been included for symbolizing these data in the Esri environment.