Mount St. Helens, in southwestern Washington, is one of the many steep-sided and often snow-covered stratovolcanoes, otherwise known as composite volcanos, that line the Cascade Range. “It actually looked really similar to a lot of the other stratovolcanoes,” says Jessica L. Ball, volcano hazards and communication specialist at the USGS California Volcano Observatory. “It was considered one of the most beautiful and symmetrical.”

That all changed, of course, on May 18, 1980, when, after two months of earthquakes and steam explosions, Mount St. Helens violently erupted, blowing its own top off and spewing massive quantities of debris across a 230 square mile blast zone. As an ash cloud from the eruption began circling the globe, mudflows choked the Toutle River and other waterbodies, bulldozing everything in their path and behaving “like a flood of wet concrete,” Ball explains.

In the end, 57 people died in the eruption, including scientists, loggers, campers and journalists, most from thermal burns or inhaling hot ash. Hundreds of buildings were destroyed, along with bridges, and vast tracts of forest were wiped out.

Scientists learned a lot from the eruption, Ball says, noting “they weren’t expecting the sideways blasts to happen.”

Today, the landscape around Mount St. Helens is gradually recovering. “It’s a lot greener, there’s a lot more larger plants establishing themselves, there’s probably a lot more wildlife in those places,” Ball says. “It’s definitely happening on a human timescale.”

Even so, another eruption is expected at some point. In a 2018 report, the USGS ranked Mount St. Helens as posing a greater threat than all but one other U.S. volcano. Additional high-threat volcanoes in Washington include Mount Rainier, Mount Baker and Glacier Peak.

Visible from Mount St. Helens on a clear day, Mount Hood stands across the border in Oregon. Another stratovolcano, as well as the state’s highest peak, it has been active for at least 500,000 years. Its last major eruptions occurred around the 1780s in what’s known as the Old Maid eruptive period. At that time, pyroclastic flows and mudflows moved down riverbeds and a new lava dome popped up on the volcano’s south flank. When Lewis and Clark journeyed to the area in 1805, they witnessed some of these eruptions’ after-effects.

In the mid-1800s, settlers reported seeing minor volcanic activity at Mount Hood. Since then, “it hasn’t had much happening,” Ball says, although steam vents still emit sulfurous gas. “There’s no sign of eruptions right now,” Ball says, “but because of its proximity to Portland and Vancouver, Washington, that’s certainly very closely monitored.

“All the Cascades volcanoes have this cycle where they … collapse and rebuild and collapse and rebuild, some of them more often than others,” she says.

Mount Hood is very popular for recreation, Ball notes. The USGS ranks it sixth among high-threat volcanoes. Other high-threat volcanoes in Oregon include the Three Sisters, Newberry Volcano and Crater Lake.

At the southern end of the Cascades, in Lassen Volcanic National Park, four types of volcanoes are found: stratovolcanoes, volcanic domes, shield volcanoes and cinder cones. Hundreds of eruptions have taken place there over the past 825,000 years, according to the USGS. The most recent, at Lassen Peak from 1914 to 1917, was the last eruption in the contiguous United States before Mount St. Helens in 1980.

The 1914-1917 volcanic event involved lava flowing from the summit crater, in addition to pyroclastic flows, mudflows and an ash column that reached as far away as Nevada. Portions of the eruption were caught on film, and to this day visitors to the national park can see the so-called devastated area. No one died in the blasts, though some ranches and cabins were destroyed. “Back then, there weren’t a ton of people [there],” Ball says.

The USGS ranks the Lassen volcanic center 11th on its list of high-threat volcanoes. Other high-threat volcanoes in California include Mount Shasta, the Mono-Inyo Craters, and the Long Valley Caldera.

In September 2024, only two U.S. volcanoes were erupting, including Great Sitkin, located on a remote, uninhabited island in the Aleutian archipelago of southwest Alaska. Satellite data showed flowing lava that’s gradually filling the summit crater. Meanwhile, small earthquakes continued to be detected beneath this stratovolcano.

Great Sitkin, which started erupting in 2021, was also one of only two U.S. volcanoes with a USGS alert level of “watch,” the third level on a four-level scale that runs from “normal” to “advisory” to “watch” to “warning.” Nonetheless, of the dozens of volcanoes that line the Aleutians, the Alaska Peninsula, and Cook Inlet, Great Sitkin is not considered to be the most dangerous, ranking 46th in the USGS report.

“In the Aleutians, there are often multiple volcanoes erupting at the same time,” Ball says. “Some of them erupt lava flows, some of them just have these explosive ash and gas eruptions.”

According to the USGS, the highest-threat volcanoes in Alaska include Redoubt Volcano, which shut down the Anchorage airport when it erupted in 2009, along with Akutan Island, Makushin Volcano, Mount Spurr, and Augustine Volcano.

The Hawaiian Islands are part of a chain of volcanoes that emerged from the depths of the Pacific Ocean following several magma-spewing eruptions. These days, most volcanic activity in Hawaii centers on the Big Island, the state’s youngest and largest landmass. “It’s the one place [in the United States] you can go where you can easily see lava,” Ball says.

She explains that Hawaii is rife with shield volcanoes, which have a different shape than the stratovolcanoes of the Cascades. “Instead of a sharp, pointy peak, you have a gently sloped half dome that spreads out over a large area,” Ball says. “You could think of it like Captain America’s shield or a Roman shield.”

Kilauea, a shield volcano on the Big Island’s southeastern shore, is particularly lively. It erupted almost continuously from 1983 to 2018. Then, on April 30, 2018, the volcano’s Pu‘u ‘O‘o crater suddenly collapsed, triggering a new, months-long eruption of lava that ultimately inundated around 700 homes, along with farms, roads, and wildlands, across 13.7 square miles of terrain. In one summit explosion from that time, plumes of ash shot some 30,000 feet into the sky.

In September 2024, the volcano erupted again in a closed-off area of Hawai‘i Volcanoes National Park, though this time it did not pose an immediate threat to people or infrastructure. Kilauea also briefly erupted three times in 2023 and in June 2024.

The USGS considers Kilauea to pose the highest threat among all U.S. volcanoes. The other high-threat volcanoes in Hawaii are Mauna Loa and Hualālai.

With geysers, hot springs, steam vents, regular earthquakes and three huge volcanic calderas, the Yellowstone National Park area in northwestern Wyoming (and two surrounding states) is one of the world’s most geologically active places.

A massive “super eruption” that took place there some 2.1 million years ago emitted an estimated 6,000 times more material than the 1980 Mount St. Helens disaster and is considered among the largest volcanic events in Earth’s history. Additional colossal eruptions occurred in Yellowstone some 1.3 million years ago and 640,000 years ago.

However, no lava has flowed in Yellowstone for around 70,000 years. “It would be a very large eruption, but the thing about those eruptions is that they happen very rarely in human terms,” Ball says.

The USGS ranks the Yellowstone caldera 21st on its list of high-threat volcanoes.