The 18 Most Dangerous Volcanoes In The United States

Mount Rainier Looms over the Puyallup Valley, Washington. It's the third most dangerous volcano in the United States, according to a new USGS report. (Image: USGS)

The US Geological Survey has updated its National Volcanic Threat Assessment, ranking the most dangerous active volcanoes in the United States. To the surprise of no one, Hawaii's Mount Kilauea is ranked at the top of the list, but other potentially dangerous volcanoes — including some lurking below the public's radar — are just as worthy of concern.

The five most dangerous volcanoes in the United States, both in terms of their likelihood of exploding and their potential threat to human life and property, are Hawaii's Mount Kilauea, Washington's Mount St. Helens, Mount Rainier, Alaska's Redoubt Volcano, and California's Mount Shasta.

Such is the conclusion of the newly released "2018 Update to the US Geological Survey National Volcanic Threat Assessment," the first such update from the USGS since 2005.

The United States is a surprisingly active country when it comes to volcanoes. The lead authors of the new report, USGS scientists John Ewert, Angela Diefenbach, and David Ramsey, say the US has endured over 120 eruptions since 1980, and it's home to 10 per cent of the planet's active volcanoes. The new report opens with this rather grim assessment of the past 38 years:

Communities have been overrun by lava flows in Hawaii and 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 mudflows have choked major river ways, destroyed bridges, and swept people to their deaths. In California, noxious gas emissions have resulted in fatalities, and in Hawaii, given rise to widespread respiratory ailments.

Airborne ash clouds have caused hundreds of millions of dollars of damage to aircraft and nearly brought down passenger jets in flight in US and international airspace, and ash falls have caused agricultural losses and disrupted the lives and businesses of hundreds of thousands of people in Washington State and Alaska.

The growing risk to communities, property, and infrastructure, the USGS authors warn, highlights the importance of knowing which volcanoes present the greatest threats and to whom.

Mount Kilauea in Hawaii. (Image: USGS)

Of the 161 young and active US volcanoes listed in the report, 18 were designated a "very high threat," and 39 were listed as posing a "high threat." The remaining 104 volcanoes had threat levels that were either moderate, low, or very low. Here are the 18 most dangerous volcanoes in the United States, according to the new report:

  1. Mount Kilauea, Hawaii

  2. Mount St. Helens, Washington

  3. Mount Rainier, Washington

  4. Redoubt Volcano, Alaska

  5. Mount Shasta, California

  6. Mount Hood, Oregon

  7. Three Sisters, Oregon

  8. Akutan Island, Alaska

  9. Makushin Volcano, Alaska

  10. Mount Spurr, Alaska

  11. Lassen volcanic centre, California

  12. Augustine Volcano, Alaska

  13. Newberry Volcano, Oregon

  14. Mount Baker, Washington

  15. Glacier Peak, Washington

  16. Mauna Loa, Hawaii

  17. Crater Lake, Oregon

  18. Long Valley Caldera, California

In terms of changes from USGS's last assessment, 12 volcanoes saw their threat levels increase, while 20 slid down the list. The top 18 remain unchanged since 2005, though 11 were given lower overall threat scores.

For the 2018 update, the USGS scientists considered all the new field and laboratory research that's been done since the last report in 2005. The more scientists learn about volcanoes, the better their prediction models. In terms of factors considered in their calculations, the USGS scientists considered volcano type, seismic activity, explosive potential, recent activity level, known eruption frequency, the number of people who live nearby, and other factors.

"The updated national volcanic threat assessment presented here is not a forecast or indication of which volcanoes are most likely to erupt next," write the authors in the report. "Rather, it is an indicator of the potential severity of impacts that may result from future eruptions at any given volcano."

So just because a volcano is assessed as being on the verge of a major eruption doesn't automatically qualify it as a top threat. It must also pose danger to US citizens, property, and even overflying aircraft.

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That's why, for example, Hawaii's Mount Kilauea gets the top score. This highly active volcano is located right next to an inhabited community and a geothermal power station.

Washington's Mount Rainier, ranked third, has a hazard zone that threatens around 300,000 people, according to the USGS, the most of any active US volcano. (Troublingly, Mount Rainier is also ranked among the world's most overdue volcanoes).

The 2018 USGS update offers a comprehensive threat assessment, but as Seth Borenstein of the Associated Press reports, it could be better:

Denison University volcanologist Erik Klemetti said the United States is "sorely deficient in monitoring" for many of the so-called Big 18.

"Many of the volcanoes in the Cascades of Oregon and Washington have few, if any, direct monitoring beyond one or two seismometers," Klemetti said in an email. "Once you move down into the high and moderate threat (volcanoes), it gets even dicier."

Because of past activity, Alaska volcanoes tend to have a more extensive monitoring system, said Tom Murray, USGS's volcano science centre director.

In addition to better monitoring, many of the threatened regions would be wise to plan for the worst. And indeed, this is already happening; in Pierce County, Alaska, the home of Mount Rainier, officials have already outlined a hazards response plan.

In case you were wondering about the Yellowstone Caldera — the supervolcano voted most likely to destroy large swaths of the United States — it's ranked 21st on the list, with a "high" threat level. As potentially dangerous as this volcano is, it's not doing anything at the moment to suggest an eruption is imminent. If anything, it's a distraction, taking our attention away from the volcanoes that deserve it most.

[USGS]