for National Geographic News
Spewing ash and steam miles into the sky, Alaska's Augustine Island volcano has been erupting this week (see photo) and posing a threat to air traffic.
The newly vigorous mountain is just one of the 18 most dangerous U.S. volcanoes, according to a report presented by John Ewert at a meeting of the American Geophysical Union in San Francisco last month. Ewert is a Vancouver, Washington-based volcanologist with the U.S. Geological Survey.
The overview ranks the United States' 169 volcanoes according to their threat levels and assesses the monitoring activity at each. The study authors aim to guide efforts to improve monitoring of U.S. volcanoes.
Ewert and colleagues based the threat rankings on frequency of eruptions and risks posed to nearby populations, infrastructure, and air traffic, among other factors. The more dangerous the volcano, the thinking goes, the better the early-warning system it should have. (Test the threat: Build a virtual volcano.)
Eighteen U.S. volcanoes are designated "very high threat"the report's highest threat level.
Most Dangerous U.S. Volcanoes, in Descending Order
1. Kìlauea, Hawaii
2. Mount St. Helens, Washington State
3. Mount Rainier, Washington State
4. Mount Hood, Oregon
5. Mount Shasta, California
6. South Sister, Oregon
7. Lassen Volcanic Center, California
8. Mauna Loa, Hawaii
9. Redoubt Volcano, Alaska
10. Crater Lake area, Oregon
11. Mount Baker, Washington State
12. Glacier Peak, Washington State
13. Makushin Volcano, Alaska
14. Akutan Island, Alaska
15. Mount Spurr, Alaska
16. Long Valley caldera, California
17. Newberry Crater, Oregon
18. Augustine Island, Alaska
Only three of the most dangerous U.S. volcanoes are sufficiently monitored, according to the report: Kìlauea in Hawaii, Mount St. Helens in Washington State, and the Long Valley caldera in California.
"We do need more monitoring," said Stanley Williams, a volcanologist at Arizona State University in Tempe. "There are few volcanoes that are really being studied at a very close level."
Williams, who was not involved with the USGS study, said better monitoring of volcanoes would allow scientists to more accurately forecast eruptions. It would also allow experts to collect detailed information on what causes volcanoes to stir. Such information would help volcanologists to better distinguish routine rumblings from signals of unrest.
"People who have hurricanes to study have it nice and easy," Williams said. "They know they have six months to test instruments, to make measurements and six months to work on the data and upgrade things, whereas when volcanoes are erupting is unknown."
Instead, volcanologists can only put their monitoring equipment in place and wait.
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