Located in the south part of the San Francisco Volcanic Field, Flagstaff’s horizon is layered with volcanoes. There is Humphrey’s Peak, Mount Elden and Sunset Crater just to name a few. They have all been dormant with Sunset Crater last erupting nearly 1,000 years ago. However, a United States Geological Survey (USGS) report from October is now calling the field a moderate threat.
A previous survey in 2005 also classified the area as a moderate treat, according to USGS Volcanologist John Ewert, who worked on both reports. The recent survey has confirmed the results of the 2005 survey.
There are about 600 volcanoes in the San Francisco Volcanic Field, which stretches from Williams to east of Flagstaff as Michael Ort, professor at NAU’s School of Earth and Sustainability, explained.
“Pretty much every hill you see around here is volcanic,” said Ort.
There are a few different types of volcanoes in the field, but the area is mostly made up of cinder cones. They aren’t the typical type of volcano that people think of.
Cinder cones shoot lava out of the ground, which can be flat or hilly. The cone shape is created when chunks of lava solidify in the air during an eruption by the time they hit the ground and accumulate, according to Ort.
The question is should people be concerned about the volcanic field? The short answer is no.
While any area can erupt at any time without warning, the probability of that occurring is astronomically low. Ort stated the moderate classification just means we should be aware.
Ort also said there are many factors considered when geologists classify the risk of a volcanic region.
“We look into a lot of things, including the chance of an eruption, how big that eruption might be and then who’s in the way. And, you combine those things together to figure out sort of the risk,” Ort said.
Ort explained the San Francisco Volcanic Field erupts on average about every 10,000 to 15,000 years. However, the moderate threat classification does doesn’t spell out when the next eruption is likely to happen.
According to Ort, the likelihood of an eruption during our lifetime is quite small. However, there may have been magmatic activity in the area a few years ago.
“About five or six years ago, there’s some evidence that down sort of between [Sunset Crater] and [Wupatki National Monument] there was an intrusion,” Ort said. “Magma came up and it was breaking the rock as it came, and it stopped, and so that may have been a bit of magmatic activity that didn’t break the surface.”
He further explained that figuring out when the magma will break the surface is not an exact science.
“Nine out of 10 times we think that what happens, is it doesn’t break the surface, it’s one out of 10 times that it does, and knowing which of those 10 is going to do it is a hard question,” Ort said.
It is not proven that this was magmatic activity, but Ort said the type of earthquakes that were produced looked like ones caused by magma moving toward the surface.
Despite the moderate threat, Ort stated there isn’t anything to worry about, but said it was a good idea to have a plan ready just in case.
“With a moderate threat volcano, I wouldn’t stay up at night worrying. I would develop the response plans for an eruption and have those ready,” Ort said.
In the extremely rare event that Flagstaff experiences a volcanic eruption, it has a response plan in place already, created by Coconino County Emergency Management.
The Coconino County Multi-Jurisdictional Hazard Mitigation Plan does not have a specific procedure for a volcanic eruption, but Todd Whitney, Coconino County director of emergency management, explained that they are prepared for any type of natural disaster.
“We’ve adopted an approach of all hazards. So, whether it’s a fire, flood or another disaster like a volcano, we would employ the all hazards approach,” said Whitney.
If evacuation becomes necessary, the county would partner with the City of Flagstaff and other agencies. Whitney stated local law enforcement would have a say as well.
“There is legal authority with the police department to issue evacuation orders. And then, we would help support those evacuation orders however they would see fit,” Whitney said.
Despite the plans having been drawn up, there has been no use for them as the San Francisco Volcanic Field continues to remain dormant.