Area of cooling lava flows and burned 'No Litter' sign.

Volcanic Activity

Volcanic Activity occurs via vents that act as a conduit between the Earth's surface and inner layers, and erupt gas, molten rock, and volcanic ash when gas pressure and buoyancy drive molten rock upward and through zones of weakness in the Earth's crust.

In the National Risk Index, a Volcanic Activity Risk Index score and rating represent a community's relative risk for Volcanic Activity when compared to the rest of the United States. A Volcanic Activity Expected Annual Loss score and rating represent a community's relative level of expected building and population loss each year due to Volcanic Activity when compared to the rest of the United States.

A map of the United States colored by Volcanic Activity Risk Index ratings. Volcanic Activity risk is prevalent in Hawaii, Washington, Oregon, California, and Alaska. For full results, see the National Risk Index Map webpage.

Volcanic Activity Exposure

A Volcanic Activity exposure value represents a community's building value (in dollars) and population (in both people and population equivalence) exposed to Volcanic Activity.

Volcanic Activity Annualized Frequency

A Volcanic Activity annualized frequency value represents the average number of recorded Volcanic Activity hazard occurrences (events) per year over the period of record (11,328 years).

Volcanic Activity Historic Loss Ratio

A Volcanic Activity historic loss ratio is the representative percentage of the exposed consequence type value (building or population) expected to be lost due to a Volcanic Activity hazard occurrence.

Volcanic Activity Processing Methodology

For comprehensive details about the Volcanic Activity processing methodology, see the National Risk Index Technical Documentation.