Yellowstone Volcano Eruption Fears Triggered by California Earthquakes

After two strong earthquakes hit in California last week, there was a spike in internet searches for Yellowstone caldera and Yellowstone volcano. The quakes—a magnitude 6.4 and 7.1 on July 4 and 5 respectively—had apparently raised fears an eruption at the supervolcano could be triggered by these events. Related search terms, according to Google Trends, included "California earthquake" and "the big one California."

But these fears are completely unfounded, the USGS has said. In an article on the Yellowstone Volcano Observatory website, scientist-in-charge Mike Poland has explained what impact earthquakes have on volcanic activity—and why the quakes in California will not cause Yellowstone to erupt.

He said that strong earthquakes are not a rare occurrence for the western U.S. The region is covered in fault lines—an interactive map of them can be found here. Fault lines are cracks in the Earth's crust that have the potential to trigger earthquakes when they move around.

"Since 1900, in the continental U.S. there have nearly 100 earthquakes greater than M6, and there have been nine greater than M7 (both of these numbers go up if you include Canada and Mexico)," Poland wrote. "Most of these events are in California, but they have also occurred in Oregon, Washington, Nevada, Utah, Idaho, Montana, and Wyoming. If we assume that rate is representative of the average, that means there would be about 10 M7+ events per century in the western USA."

It has been 70,000 years since Yellowstone last erupted. Over this time, there may have been over 7,000 strong earthquakes—none of which have led to an eruption at Yellowstone. Poland also said that the distance of the earthquake to Yellowstone does not matter—in 1959 a magnitude 7.3 earthquake hit on the Montana-Idaho border, on the boundary of the National Park, but there was still no eruption.

California volcanoes

California also has its own volcanoes. The USGS recently released a report saying that the next big hazard to hit the state could be a volcano rather than an earthquake—"The potential for damaging earthquakes, landslides, floods, tsunamis, and wildfires is widely recognized in California," the report said. "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."

There was no concern the two strong earthquakes would trigger an eruption at any of California's volcanoes.

Last Saturday, California Volcano Observatory released a statement saying that a magnitude 5.4 earthquake (an aftershock of the 7.1 event) had triggered an earthquake swarm at the Coso Volcanic Field. However, the volcano alert level was kept at normal and it said there "is no imminent threat of an eruption."

As Poland explains: "Earthquakes like those of the past week are unlikely to trigger volcanic eruptions, although they might trigger microearthquakes at some volcanoes… Based on seismic data, we can see that these smaller quakes start at the same time as the waves from the distant large earthquake arrive. Some of these triggered swarms have lasted for days."

He said strong earthquakes can also lead to changes to hydrothermal systems including the geysers found in Yellowstone National Park. "But triggering eruptions? That's not common, especially in the mainland U.S.," Poland concludes.

Following the earthquakes, concerns were also raised about the "Big One" being triggered. This is the idea that the San Andreas Fault—a 750 mile fault that runs close to San Francisco, Los Angeles and San Diego—is "overdue" a large earthquake.

This is based on the idea that there is an average length of time between large earthquakes on a given fault—as pressure builds over time to the point where it is released. The last time there was a strong earthquake on the San Andreas Fault was 1906, when a magnitude 7.8 earthquake hit the San Francisco area, causing widespread damage and hundreds if not thousands of deaths.

Yellowstone Grand Prismatic Spring
File photo. Yellowstone Grand Prismatic Spring iStock