The government ranks 18 US volcanoes as "very big threat"

WASHINGTON – Government scientists have classified 18 US volcanoes as "very high threat" because of what is happening inside them and their proximity to humans.

The US Geological Survey has updated its assessments of the threat of a volcano for the first time since 2005. The Hazard List is at the top of Kilauea Hawaii, which has been updated this year. The other top five are Mount St. Helens and Mount Rainier in Washington, Redoubt Volcano in Alaska, and Mount Shasta in California.

"This report may surprise many people, but not volcanologists," said Janine Krippner, an expert in volcanology at Concord University. "The United States is one of the world's most active countries in volcanic activity," she said, noting that 120 eruptions have occurred on US volcanoes since 1980.

Eleven of the 18 very high threat volcanoes are found in Oregon, Washington, and California.

Government scientists use a variety of factors to calculate an overall threat index for each of the country's 161 active young volcanoes. The score is based on the type of volcano, its explosiveness, its recent activity, its frequency of occurrence, the number of people living nearby, the evacuations that occurred in the past and the eruptions disrupt air traffic.

They are then classified into five threat levels ranging from very low to very high.

The volcanologist Erik Klemetti of Denison University said the United States was sorely lacking in surveillance for many of the so-called Big 18s.

"Many of Oregon's and Washington's Cascades volcanoes have little or no direct monitoring beyond one or two seismometers," Klemetti said in an email. "Once you descend into the high and moderate threat (volcanoes), it becomes even more difficult."

The USGS said that a dozen volcanoes had increased their threat level since 2005. Twenty others have dropped their threat level.

Scores and threat levels are changing due to better information on volcanoes, said Klemetti.

Among those where the threat score – but not the threat level – is higher are the Alaskan Redoubt, Mount Okmok, Akutan Island and Mount Spurr. Threat scores also increased for Newberry Volcano (Oregon) and Yellowstone (Wyoming).

None of the 18 major groups have changed global threat levels, although 11 have had overall threat scores down.

In addition to the top 5, the other 18 are Mount Hood, Three Sisters and Crater Lake, Oregon; Akutan Island, Makushin, Mount Spurr and Augustine Alaska; Lassen and Long Valley, California; Mount Baker and Glacier Peak in Washington; and Mauna Loa in Hawaii.

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Follow Seth Borenstein on Twitter: @borenbears.

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