To uce the rankings, the USGS uses a 24-factor hazard and exposure matrix, assessing explosive activity in the past 500 and 5,000 years, frequency of eruptions, and the level of impact an eruption could have on local populations, airplanes, transportation and power infrastructure.

SetMoran, director of the USGS Cascade Volcano Observatory, said he’s used the rankings to strategically prioritize where to place additional seismometers — instruments that measure volcanic activity — over the past four years. One of those mountains was Rainier.Ten years ago, several stations were added to Mount Rainier in conjunction with the University of Washington, making it one of the better detection networks in the Cascades, Moran said. More recently, technology to detect lahar movements has been put in place. Lahars are large volcanic mudflows generated by the collapse or eruption of a volcano.Moran said even though nothing has changed since the last report, people in Washington should remain alert.“Like any other hazard, after a while you get used to it, but it’s important to not get used to it,” he said.More Photo Galleries Meanwhile, population booms around the state didn’t make the volcanoes around Washington any more dangerous than they already are, Moran said. On the bright side, because most are fairly cold due to their last eruption occurring many thousands of years ago, it would take them some time to warm up and erupt, giving everyone a chance to get to safety.The report describes just how catastrophic it was when Mount St. Helens erupted in 1980, the most recent in the state’s history.Sign up for Morning BriefDelivered bright and early weekday mornings, this email provides a quick overview of top stories and need-to-know news.“In Washington state, a powerful explosion has devastated huge tracts of forest and killed people tens of miles from the volcanic source, and debris avalanches and mud flows have choked major river ways, destroyed bridges and swept people to their deaths,” the report said. “Ash falls have caused agricultural losses and disrupted the lives and business of hundreds of thousands of people in Washington state.”The death toll from the Mount St. Helen is estimated at 57 people.Agueda Pacheco-Floresapacheco@seattletimes.comon Twitter: @AguedaPachecOh.