In addition to fires, floods, earthquakes, and tsunamis, Californians are also subject to volcanic threats from the 8 volcanic areas classified as moderate, high, and very high threat in the state. These threat level classifications are defined and assigned in the USGS National Volcanic Threat Assessment released in 2018.
Volcanic eruptions in the state are not currently imminent. Using the threat levels, these volcanic areas are monitored continuously by Cal OES, for emergency managment considerations and by the USGS California Volcano Observatory, for scientific observations of potential consequence. Almost all of the 8 significant volcanic areas are known for their local geothermal features, some of which produce energy for Californians.
The USGS has now released report 2018-5159 entitiled California's Exposure to Volcanic Hazards. Cal OES will use this important report along with the recently released National Volcanic Threat Assessment to initiate state level response planning.
Volcanic eruptions and earthquakes are a way for Earth to release pressure and heat, much like a safety valve. A volcano is basically a vent, or opening, in the earth’s crust from which hot molten rock, gases, and volcanic ash escape to the surface. They may erupt explosively like Krakatoa in 1883, or effusively seep out lava like the Kilauea volcano. Formed as a result of plate tectonics, volcanic eruptions can result in the formation of mountains, craters, crater lakes, plateaus, and islands. Volcanoes are classified as active, dormant or extinct. An active volcano is the one that erupts or causes seismic activity on a regular basis over hundreds or thousands of years. A dormant volcano is one that has not erupted for a very long time, but could erupt again in the future. And, a volcano that has been dormant for more than 10,000 years is considered an extinct volcano. See our “Tools and Resources” Section below for more information.
If you are near a volcano and watching for signs that it may erupt, here are some clues you might look for: 1. An increase in seismic (earthquake) activity occurs prior to an impending eruption as the magma and gasses move below the surface. The magnitude of the earthquakes may be small.2. If you are looking at the cracks of a volcano’s surface, you may see vents (called fumaroles) that release pressure from the gasses below. If you see an increase in gases escaping from these vents, or a change in the temperature of the gases, this can signify a potential eruption.3. Scientists can determine if the magma has thickened. If so, it may trap gases under it which can lead to an eruption4. A sudden rise in the elevation of the ground and the appearance of new cracks may be a sign of an upcoming eruption.5. Changes in the groundwater temperature may occur prior to eruption.
Scientists routinely monitor seismic activity near volcanoes which allows them to assess any unusual activity. They can also monitor gas, ground deformation and satellite imagery to determine if magma is rising toward the surface. This information can be assessed quickly and volcanic hazard information can be communicated as real-time warnings to prevent loss of life. To sign up for email notifications, go the Unites States Geological Survey, Volcano Notification Service website. It only takes a minute and there is no cost.
The U.S. Geological Survey (USGS) Volcano Hazards Program uses an alert-notification system to indicate the level of potential danger for volcanoes. Color-coded triangular signs are posted along with hazard details.
Normal/Green The normal/green icon is used when background activity is within the range of typical non-eruptive phenomena seen at the volcano. Advisory/Yellow The advisory/yellow icon is used when a volcano is exhibiting signs of elevated activity above normal ranges. Watch/Orange The watch/orange icon is used when heightened or escalating unrest is exhibited with an increase in potential for eruption. In this stage the timeframe is unclear or an eruption is occurring posing limited hazard with no or minor emissions of volcanic ash. Warning/Orange The warning/orange icon is used when a major eruption is suspected, underway, or imminent, but no or minor volcanic ash emissions to impact aviation (lava flows only). Watch/Red The watch/red icon is used when an eruption occurs with limit hazard to ground based committees (little to no lava flow), but significant impacts to aviation with substantial emissions of ash in the atmosphere. Warning/Red The warning/red icon is used when a major a major eruption is suspected, underway, or imminent, with significant hazards expected to both ground based communities, and aviation. Unassigned The unassigned icon is used when ground-based instruments are unable to determine that a volcano is within normal parameters.
List of Volcanoes in California (USGS California Volcano Observatory)
List of Volcanoes in the United States (USGS CalVO)
Volcanic Monitoring (USGS)
Volcano Eruption Fact Sheet (multiple languages and large font) (Washington State Dept. of Health)
Volcano Hazards Program Feeds (USGS)
Volcano Hazards Program Fact Sheets and Posters (USGS)
Volcano Frequently Asked Questions (USGS CalVO)
How Volcanoes Work (San Diego State University)
Learn about U.S. Volcanoes (USGS CalVO)
Planning and Preparedness for Governments and Tribal (CalOES)
Volcanic Ash Facts and Guidance (USGS)
Volcanoes: Earth's Fiery Power (National Geographic)
What Causes Volcanoes to Erupt? (Buzzle)
How Volcanoes Work (San Diego State University, et al.)
Kids Tour to Mars - Volcanoes (Kid's Cosmos)
School Planning and Preparedness (CalOES)
Virtual Volcano Field Trips (Oregon State University)
Volcano Games (Oregon State University)
Volcano Resources for Educators (USGS)
The Business and Industry Council for Emergency Planning and Preparedness (BICEPP)
Emergency Management Guide for Business and Industry (FEMA)
Emergency Preparedness Checklist for Small Businesses (FedEx)
Emergency Preparedness Resources for Business (FEMA)
Five Steps to Develop your Business Preparedness Program (CalOES)
Ready.gov for Business (FEMA)
U.S. Department of Homeland Security
U.S. Small Business Administration (SBA)
Volcano Safety Tips (ARC)
Key Facts about Preparing for a Volcano Eruption (CDC)
Key Facts about Protecting Yourself after a Volcanic Eruption (CDC)
Prepare for a Volcanic Eruption (US EPA)
Volcano Ready.gov (FEMA)
Recover After a Volcanic Eruption (US EPA)
American Red Cross (ARC)
California Volcano Observatory (CalVO)
NOAA Volcanic Ash Advisory Center
Seismic Safety Commission – Volcanoes
United State Environmental Protection Agency (US EPA)
United States Geological Survey: Volcano Notification Service