VolcanoesWhich U.S. volcanoes pose a threat?

Published 22 February 2019

The United States is one of Earth’s most volcanically active countries. Since 1980, there have been 120 eruptions and 52 episodes of notable volcanic unrest at 44 U.S. volcanoes. An updated USGS assessment finds that 161 U.S. volcanoes pose potential threats to American lives and property, eight fewer than in 2005. The eighteen very highest threat volcanoes are in Alaska, California, Hawaii, Oregon and Washington. Thirty-nine other volcanoes are high threat, 49 are moderate, 34 are low, and 21 are very low threat.

As part of its program of keeping officials and the public apprised of volcanic threats, the USGS periodically reassesses the threat level of U.S. volcanoes and updates volcanic threat assessment documentation. In 2005, the USGS published its first national volcanic threat assessment in support of establishing a National Volcano Early Warning System. The assessment helps to prioritize U.S. volcanoes for research, monitoring and mitigation efforts based on objective measures of volcano hazards and exposure of people and infrastructure to those hazards. The new report is an update of that assessment.

“More than ten percent of the world’s known active and potentially active volcanoes are within U.S. territories,” said John Ewert, a USGS geologist and lead author of the updated Volcanic Threat Assessment. “All of these volcanoes pose some degree of risk to people and infrastructure.”

Ewert and his USGS colleagues applied specific criteria to each volcano to derive a score, and grouped volcanoes into five threat categories. “The ranking is not a list of which volcano will erupt next,” said Ewert; “instead, it is a way to help focus attention and resources where they can be most effective.”

The United States is one of Earth’s most volcanically active countries
USGS notes that since 1980, there have been 120 eruptions and 52 episodes of notable volcanic unrest at 44 U.S. volcanoes.

The mountainous landscapes of California, Oregon, Washington, Alaska, Hawaiʻi, American Samoa and the Mariana Islands are punctuated by volcanoes. Born along the margins of converging tectonic plates or above intraplate hot spots, these volcanoes are a part of our country’s history and culture. But when erupting, these same volcanoes threaten the health and safety of residents and can damage property and infrastructure.

·  In 2018, more than 700 structures were destroyed when swift-flowing lava erupted from fissures in Kīlauea Volcano’s lower East Rift Zone. Lava covered 35.5 square kilometers (13.7 square miles), which included homes, farms, wild spaces, roads, highways and critical infrastructure. Kīlauea is ranked as the U.S. volcano with the highest threat score in the very high threat category.

·  In 1980, a powerful explosion at Mount St. Helens devastated huge tracts of forest and killed people tens of miles from the volcanic source, while debris avalanches and mudflows choked major rivers and destroyed bridges. Mount St. Helens is ranked a very high threat volcano.