The data that he and Buesch collected included photographs and notes documenting the size, type and location of rocks that were lifted off the ground and moved short distances by pyroclastic flows during the ancient eruption.  Supervolcanoes capable of unleashing hundreds of times the amount of magma that was expelled during the Mount St. Helens eruption of 1980 are found in populated areas around the world, including the western United States. So, Roche and others looked at the sizes of blocks picked up by and incorporated into the Peach Springs Tuff (see above).
– Think supervolcanoes that devastate entire regions are terrifying? Well sure, but you might be able to outrun them—according to a study that says one prehistoric supervolcano churned out lava at only 10 to 45 miles per hour, Live Science reports. "It's really interesting how you can have such a violent eruption producing such slow-moving flows," says study co-author Greg Valentine. "They still devastate a huge area, but they're slow and concentrated and dense." Published in Nature Communications, the study analyzed an Arizona supervolcano known as Silver Creek Caldera that erupted 18.8 million years ago. It churned out lethal tides of gas and ash known as pyroclastic flows for over 100 miles, inundating parts of Nevada and California, ScienceDaily reports. By analyzing the vast volcanic deposit left by Silver Creek Caldera, researchers found that large rocks had been moved considerable distances. Their conclusion: Only a constant, heavy flow would have moved rocks that were already miles from the eruption. Not everyone buys it, and the researchers warn against taking their study as an excuse for last-minute evacuations. What's more, smaller eruptions (like the one that wiped out Pompeii) are known to spew pyroclastic flows at hundreds of miles per hour, Wired reports. But it seems anyone 90 miles away from Silver Creek Caldera would have had about 10 hours to escape. "I wouldn't recommend anyone try to outrun a volcano, but there's a few of us that could," says Valentine. (Parts of Washington and Oregon were covered in mysterious ash last year.)