These are the most dangerous U.S. volcanoes, scientists say

Molten rock poured like water from Hawaii's Kīlauea volcano this summer, destroying hundreds of homes. PHOTOGRAPH BY STEVE AND DONNA O'MEARA, NAT GEO IMAGE COLLECTION

Molten rock poured like water from Hawaii's Kīlauea volcano this summer, destroying hundreds of homes. PHOTOGRAPH BY STEVE AND DONNA O'MEARA, NAT GEO IMAGE COLLECTION

In the wake of its recent fiery rampage, it's perhaps no surprise that Kīlauea in Hawaii tops the list as the most dangerous volcano in the U.S., according to newly released rankings from the U.S. Geological Survey. Washington's Mount St. Helens and Mount Rainier round out the top three slots.

The new volcano threat assessment is an update to a 2005 report that determined the greatest risks based on the potential for eruption and human impacts. To be clear, the report does not forecast the volcanoes most likely to erupt—it is merely a ranking of the “potential severity of impacts” of future hypothetical eruptions.

“The threat articulated in this report is the same threat that was there a week ago,” says Ben Andrews, the director of the Smithsonian's Global Volcanism Program. “It's maybe just a little better described here.”

Such rankings provide vital information so that the USGS and other organizations can determine which volcanoes deserve the most attention for research, monitoring, emergency planning, and funding. By doing so, these groups can more effectively help local communities react to future eruptions.

“It's so critical,” volcanologist Janine Krippner of Concord University says of the report. Volcanology funding is limited, she notes, so the ranking helps scientists and government officials home in on the biggest dangers and try to avert disaster.

“Volcanoes tend to give us warning before they erupt,” Krippner says. “But if we're not listening, we'll miss it.”

How volcanic is the United States?

The United States is one of the most volcanic countries in the world, boasting more than 10 percent of the planet's active or potentially active volcanoes. The latest report identifies 161 volcanoes of concern, the majority of which cluster along the nation's western coast through California, Washington, Oregon, and Alaska.

This intense activity is driven by the underlying collision of tectonic plates, where the denser oceanic plate is being shoved beneath the North American continental plate. As the ocean slab plunges deep into the planet, temperatures and pressures climb, causing water to escape. The presence of water reduces the melting point of the rocks overhead, forming magma. If that molten material makes it to the surface, a formerly quiescent peak can burst to life in an eruption. (Here's what may happen when Earth's plate tectonics stop.)

But the West Coast isn't the only place in the country with potential for volcanic activity. Though they're placed at a much lower threat level, volcanoes in Arizona, Colorado, and Utah also make the list.

“The reason why they are there is much debated,” Adam Kent, a volcanologist at Oregon State University, says of these interior volcanoes. They could be powered by hotspots, where an underlying plume of magma lurks. This is the mechanism behind the Hawaiian island chain, which formed as its tectonic plate crept over a largely stationary plume. Kent likens the process to a conveyor belt moving over a blowtorch.

A volcanic hotspot is also the explanation for the infamous Yellowstone caldera, which ranks just 21 on the new list. Though its supervolcano status has sparked a lot of bluster over the years, it's unlikely it will erupt anytime soon.

“I want to emphasize this in bold, underlined, blinking text: We are in no way overdue for an eruption in Yellowstone,” Andrews says.

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