California’s Sleeping Giants: How Cal OES Monitors Local Volcanos


On May 18, 1980, Mount St. Helens erupted at 9:15 a.m., not only spewing clouds filled with ash, but also claiming the lives of dozens of people. More than 40 years later, this anniversary is a reminder of what the California Governor’s Office of Emergency Services (Cal OES) is doing to be prepared for the next one.

California is home to a variety of volcanoes, many of which most people are not aware. See a list of volcanoes in California.

Volcanos in California

Volcanic eruptions in the state are not currently imminent, but in addition to fires, floods, earthquakes, and tsunamis, Cal OES’ Seismic Hazards Branch monitors any possible volcanic threats from the eight volcanic areas classified as moderate, high, and very high threat in the state.

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.

Mount St. Helens – Two Months of Warnings

On March 16, 1980, Mount St. Helens awoke when a series of small earthquakes began. Hundreds more occurred over the next 11 days. On March 27, a steam explosion created a crater through the summit ice cap. A week later the crater had grown to 1,300 ft wide and two giant cracks crossed the entire summit of the mountain. By May 17, two months after the volcano first awoke, over 10,000 earthquakes had shaken the mountain, due to magma rising high into the volcano.

On May 18, a magnitude 5.1 earthquake occurred, and the volcano’s summit slid away in a huge landslide—the largest on Earth in recorded history. The blast reached 17 miles north, and the debris from the landslide slid 14 miles west down the North Fork of the Toutle River.

Geologists are credited with saving many lives by evacuating the area around the volcano before the large landslide eruption occurred. These scientists convinced local authorities to limit access to the area around the volcano and to keep it closed. There were two months between the time the volcano awoke with earthquakes until the time it finally blew.

Prepare your Home and Family

Preparing your family for a possible volcanic eruption will not only help protect your health and property, but also may be the difference between life and death. Below are steps you can take to minimize impacts to your family and home in the event of volcanic eruption:

  1. Know where the active volcanoes are in your area and how close you are to them.
  2. Take into account anyone with functional and/or access needs, children, pets, and livestock.
  3. Create an emergency evacuation plan with your family. Review it often so that each person knows what to do, how to find each another if you’re apart, and how to contact neighbors and/or emergency services if you cannot get away from the property using your own transportation.
  4. Create an emergency kit for your car including maps, tools, a first aid kit, a fire extinguisher, flares, additional non-perishable food, booster cables, sleeping bags and/or emergency blankets, and a flashlight.
  5. If there are disaster warning sirens in your area be aware of what they sound like. When a volcanic eruption occurs, you’ll want and need to listen for them.
  6. Know how to turn off all utilities.
  7. Obtain proper respiratory protection such as an air purifying respirator, also referred to as an N-95 disposable respirator.
  8. Review your homeowner’s insurance policy, and if necessary, increase your level of coverage to ensure you are covered adequately.

To learn more about our local volcanos and other tools and resources available, visit the Cal OES Seismic Hazards Branch page here.