File photo – the Shasta volcano in California, United States
(Photo by Gerard SIOEN/Gamma-Rapho via Getty Images)
For years now, California has been bracing for the “big one” — the magnitude of 6.7 or higher magnitude earthquake that is expected to send ripples through the state within the century. But there is still a deadly threat that is almost as likely, and that people are much less prepared for.
In the next 30 years, there is a 16 per cent possibility of a small to moderate size volcanic eruption takes place somewhere in California, according to a U.S. Geological Survey (USGS) report posted on Monday (Feb. 25). This prediction is based on 5000 years of volcanic activity records. About 200,000 people live or work in a region on the risk of an eruption, and millions of people visit each year, according to the report.
In comparison, there is a 22 percent of the possibility that there is an earthquake on the San Andreas Fault — also known as “the big one” — will hit within that time frame.
“The potential for damage from earthquakes, landslides, floods, tsunamis, forest fires is widely recognized in California,” the researchers wrote in the report. “The same cannot be said for volcanic eruptions, despite the fact that they occur in the state about as frequently as the largest earthquakes on the San Andreas Fault.”
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There are systems for the detection of possible volcanic eruptions — but the understanding of the risks in specific parts of the state is important for reducing damage and loss of life from such events, they wrote.
There are eight volcanic areas in the entire country, that experts say are “threatening” to people or property in the neighborhood, according to the report. At least seven of the eight volcanoes sit above magma, and are therefore considered “active”. [Countdown: the History of the Most Destructive Volcanoes]
Of these, Mount Shasta, Medicine Lake volcano and Lassen Volcanic Center in Northern California, and the Salton Buttes near the southern border, have erupted in the last 3000 years and are considered as high to very high risk areas. The Long Valley Volcanic Region in the east has also emerged in that time, but is considered to be moderate to very high risk. And the Clear Lake Volcanic Field north of San Francisco is also regarded as high to very high risk, although it has not yet been broken in the last three millennia.
A volcano can cause widespread damage, even if it does not erupt, according to the report. An erupting volcano can lead to ballistic showers of rocks, fast-moving flow of ash and lava called pyroclastic flows and acid rain. But even volcanoes that are not currently eruption can lead to hazards terrain around the volcano can become unstable and can lead to landslides, for example.
Although these effects are most strongly felt near the site of an eruption, mudslides or floods, it can reach more than 50 miles (80 kilometers) away and ashfall may reach areas 1,000 miles (1600 km) away, according to the report.
“Volcanic hazards are likely to be more than a local problem, limited to one country or region,” the report said. “A future eruption in northern California, for example, have an adverse effect on the natural resources and infrastructure important to our statewide water, energy and transport systems, and will certainly require a multi-jurisdictional response effort.” The eruption itself, increasing and decreasing in intensity over time, can last months, years or decades, such as the after-effects.
During volcanic eruptions cannot be prevented, they can sometimes be predicted.
The USGS California Volcano Observatory uses GPS receivers to record ground deformation, seismometers to measure shaking and spectrometers for the detection of greenhouse gases from the ground. An increase of the activity in each of these three measurements may be the first sign that a volcano will soon erupt, according to the report.
“Although the eruptions cannot be stopped, measures to limit exposure and tolerance can make the community less vulnerable to their effects,” they wrote. This includes the evacuation of hazardous areas during an eruption, making the infrastructure better to withstand the effects, quick clean-up after the event and the diverting of lava, or remove combustible material out of the way. In the case of ash fall, people can wear particle masks, avoid the drive, the sealing of buildings, livestock shelter and shelter in place.
Originally published on Live Science.