SAN FRANCISCO (CBS SF/AP) – California’s next ‘big one’ may not be an earthquake. According to a new study from the U.S. Geological Survey, a future volcanic eruption is not only inevitable, hundreds of thousands of people are in harm’s way.

The 50-page report, California’s Exposure to Volcanic Hazards, released Monday, assigns threat levels to eight volcanoes in California — moderate, high, and very high. Most of them are located in the northern and central part of the state.

READ: California’s Exposure to Volcanic Hazards

Researchers say nearly 200,000 people live, work or pass through California’s volcanic hazard zones on a daily basis, and there’s a 16 percent probability of an eruption in the next 30 years.

The scientists based the prediction on the amount of volcanism over the last three-thousand, or so, years.

“Of the eight volcanic areas that exist in California, molten rock resides beneath at least seven of these—Medicine Lake volcano, Mount Shasta, Lassen Volcanic Center, Clear Lake volcanic field, the Long Valley volcanic region, Coso volcanic field, and Salton Buttes—and are therefore considered “active” volcanoes producing volcanic earthquakes, toxic gas emissions, hot springs, geothermal systems, and (or) ground movement,” says the report.

Mount Shasta has the largest number of people in harm’s way, with a daily population of more than 100,000. The threat level there is very high, according to the report.

Overall, “an average of 199,235 people live, work, or pass through a California volcanic hazard zone on a daily basis,” it says.

Most of the active volcanoes lie in Northern California. The report warns a future eruption would have far-reaching adverse impacts on natural resources and infrastructure vital to the state’s water, power, natural gas, ground and air transportation and telecommunication systems.

“Overhead electric transmission lines of three of California’s major utilities pass through volcanic hazard zones, as well as about 178 associated substations,” says the report.

The impact would be not only on humans, but crops, livestock and animals, as well. Damage to crops such as hay and alfalfa would impact the state’s dairy industry.

“Exposure of agricultural crops, pastures, and livestock to volcanic ash fall can be serious, even for a light dusting. Ash fall on forage most commonly results in digestive tract problems in livestock, including gastrointestinal tract obstruction,” it says. An eruption in New Zealand killed more than 2,000 animals that grazed on pastures covered by ash.

“The next step in reducing volcanic risk involves assessing site- and sector-specific vulnerabilities and developing mitigation strategies,” says the report. “This will require the collective efforts of scientists, land managers, civil authorities, lifeline operators, and communities.”

Scientist-in-charge Magaret Mangan of the California Volcano Observatory says the report is not a doomsday scenario.

Rather, she says, it should be a springboard for launching studies of the vulnerabilities of specific sites.

Here is a list of the areas in the report, along with the most recent eruption, nearby towns and threat potential, according to the USGS.

Mendicine Lake Volcano:

Most recent eruption: 950 years ago

Nearby towns: Malin, Merrill, Tulelake, Klamath Falls (OR)

Threat Potential: High

Mount Shasta

Most recent eruption: 200-300 years ago

Nearby towns: Weed, Mount Shasta, Edgewood, Dunsmuir

Threat Potential: Very High

Lassen Volcanic Center

Most recent eruption: Between 1914 and 1917

Nearby towns: Mineral, Viola

Threat Potential: Very High

Clear Lake volcanic field

Most recent eruption: about 10,000 years ago

Nearby towns: Clearlake, Kelseyville, Lakeport, Lucerne

Threat Potential: High

Coso volcanic field (160 miles north of Bakersfield)

Most recent eruption: 40,000 years ago

Nearby towns: Olancha, Pearsonville

Threat Potential: Moderate

Long Valley Caldera volcanic region

Most recent eruption: 16,000-17,000 years ago

Nearby towns: Mammoth Lakes

Threat Potential: Very High

Salton Buttes

Most recent eruption: about 1,800 years ago

Nearby towns: Westmorland, Calipatrica, Niland, Brawley

Threat Potential: High







(KILAUEA VOLCANO: Dramatic new overnight video of the lava river flowing on the Big Island)

The USGS: Volcano Hazards Program has posted valuable resources and information to help people prepare for a volcanic event, which in some cases can last tens of years.

Residents who are exposed to the greatest risk should be aware of evacuation routes, have emergency provisions on hand sufficient for 2 weeks, and devise a plan for families to reunite in the event they are separated.

© Copyright 2019 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.