The U.S. Geological Survey has released its update to 2005’s Volcano Threat Assessment. The 2018 Report is a good read, especially if you live on the west coast, in Alaska or in Hawai’i in these United States.
But the press coverage has been a little hysterical. The Associated Press lead, for example: “Government scientists have classified 18 U.S. volcanoes as “very high threat” because of what’s been happening inside them and how close they are to people.”
At least not recently.
What the 2018 update did was apply some new information about the dates of old lava flows, changes in population around volcanoes and a bit of new scientific understanding of eruptions to the existing 2005 report. As a result of all that new information, the number of volcanoes classified as Very High Threat went from 18 in 2005 to . . . 18 in 2018. It didn’t change. Same volcanoes, too.
Threat assessment is a complicated business. The USGS weighs about 24 different factors for each volcano in North America, assigning a score to each factor. The highest scoring 18 volcanoes are those placed in the category Very High Threat. From there is scales down through High Threat, Moderate Threat, Low Threat and Very Low Threat. The only changes in ranking were in the Low Threat and Very Low Threat categories.
Not all volcanoes are explosive. Mt. St. Helens is, because it’s the product of a subducted plate. Kilauea, on the Big Island of Hawai’i, is the most active volcano in the United States – maybe in the world – but it isn’t the explosive risk that Cascade and Alaska volcanos are.
On the other hand, all of Hawai’i is built on the slopes of volcanoes. The risk of having your house buried in lava, as we saw this summer, is a lot higher when you live on the volcano. Proximity of development to volcanoes is a factor.
Famously, aircraft that fly in to ash clouds are in serious trouble, as KLM Flight 867 demonstrated when it flew through an ash cloud from Mt. Redoubt in 1989. Proximity to aircraft flight paths is factor.
Higher mountains, like the stratovolcanoes Rainier, Shasta and Hood, hold immense amounts of potential energy because of their altitude. As we saw with the eruption of Mt. St. Helens, the gravity potential of even a modest stratovolcano can transport debris immense distances. So altitude is a factor.
Alaska has 86 volcanoes in the report, by far the most of any state. We have the Aleutian Islands to thank for that dubious distinction. But that’s a net loss of four from the 2005 Report, al based on research since 2005 determining that the fie dropped volcanoes haven’t erupted in geologically recent times. Alaska added one volcano, Tana Volcano, located in the Islands of the Four Mountains, on the east half of Chuginadak Island.
Alaska has five volcanoes in the Very High Threat category: Akutan Island, Augustine Volcano, Makushin, Redoubt Volcano and Mount Spurr. WC’s adopted state, Idaho, has just four volcanoes on the list, all judged Low Threat. Of course, the Yellowstone Caldera is just a few miles east of Idaho, and it made the High Threat category.
The bottom line is that there is no “news” here. No volcanoes that aren’t erupting already – Kilauea – are threatening to erupt. The list of very dangerous volcanoes is unchanged. Yes, every volcano on the Very High Threat list is likely to erupt again. No, we don’t have a clue as to when. But in the list of things a sensible person would worry about, this one is pretty low.