18 of the Most Dangerous Volcanoes in the U.S.

The five most dangerous volcanoes in the U.S. graphic
The five most dangerous volcanoes in the U.S., according to the U.S. Geological Survey, are in Hawaii, Alaska, and the Pacific Northwest.

Treehugger / Julie Bang

There are 169 active volcanoes in the U.S., with Alaska, Hawaii, and the Pacific Northwest containing the highest concentrations. Not all of them pose an imminent threat of eruption—after all, active volcanoes can lie dormant for 10,000 years or more—but scientists believe that some of them could soon be due. In an October 2018 update to its National Volcanic Threat Assessment, the U.S. Geological Survey ranked 18 volcanoes as "very high" threats based on their eruptive history, recent activity, and proximity to people.

So, here are 18 volcanoes that could create serious problems when they finally do erupt.

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Kilauea (Hawaii)

Hot lava on coast with Kilauea erupting in background
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Kilauea is the most active of the five volcanoes that form the Big Island of Hawaii. Located on the southeastern part of the island, the shield volcano has erupted 34 times since 1952. The most recent eruption lasted almost three decades, from 1983 to 2018. Its slow-moving lava was relatively harmless for much of that period—if anything, it created spectacular scenery as it gradually expanded the Island of Hawaii—but it also sometimes sends lava through new vents with little warning. That occurred in 1990, and it destroyed much of the town of Kalapana.

A more recent reminder of Kilauea's potential danger, the volcano began invading residential neighborhoods near Pahoa in the spring of 2018. A series of new eruptive vents began spewing lava into the Leilani Estates and Lanipuna Gardens subdivisions, along with dangerous sulfur gas, destroying dozens of buildings and forcing more than 1,700 people to evacuate.

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Mount St. Helens (Washington)

Aerial view of snowy Mount St. Helens and surrounding landscape
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One of the worst volcanic eruptions in U.S. history occurred on May 18, 1980 about 50 miles northeast of Portland, Oregon. An earthquake knocked a chunk of Mount St. Helens off, triggering a landslide and a blast that shot a tower of ash up 30,000 feet, knocking down trees across 230 square miles. Subsequent eruptions sent avalanches of hot ash, rocks, and gas pummeling down the slopes at 50 to 80 mph. More than 50 people and thousands of animals were killed in all, and damages topped $1 billion.

Mount St. Helens reawakened in 2004, when four explosions blasted steam and ash 10,000 feet above the crater. The lava that continued gurgling out formed a dome on the crater floor until late January 2008, when it erupted and filled 7% of the 1980 crater. Although it's calmed down now, the USGS still calls it an "active and dangerous" volcano.

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Mount Rainier (Washington)

People hiking through forest in the shadow of Mount Rainier
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The Cascade Range's highest peak is a volcano loaded with the most glacier ice of any mountain in the contiguous U.S. This poses a threat to Seattle-Tacoma, over which Mount Rainier looms, if—or when—the stratovolcano erupts. As Mount St. Helens demonstrated in 1980, volcanoes that erupt through ice can create lahars. Two lahars from Mount Rainier made it all the way to Puget Sound following a catastrophic eruption about 5,600 years ago.

What Are Lahars?

Lahars occur when hot gas, rocks, lava, and debris mix with rainwater and melted ice and form a violent mudflow that pours down a volcano's slopes, often via a river valley.

Mount Rainier's potential volatility and proximity to large cities helped make it one of only two U.S.-based Decade Volcanoes—those the U.N. deems especially dangerous to human populations. Rainier last erupted in the 1840s, and larger eruptions occurred as recently as 1,000 and 2,300 years ago. Today, it's considered active but dormant. Still, it's one of the most intensely monitored volcanoes in the country.

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Mount Redoubt (Alaska)

Fishing boat in water in front of Mount Redoubt
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Redoubt is located in Alaska's Lake Clark National Park and Preserve, where the nearly 11,000-foot-tall stratovolcano forms the tallest peak in the Aleutian Range. It's been erupting for about 900,000 years, with its present-day cone forming about 200,000 years ago.

Redoubt has erupted at least 30 times in the last 10,000 years, with the most recent eruptions occurring in 1902, 1966, 1989, and 2009. During the 1966 eruption, melted ice from the mountain's summit crater caused a type of glacial outburst flood called jokulhlaup, Icelandic for "glacial run." Forty years later, the volcano lurched to life again for several months. It sent ash clouds as high as 65,000 feet above sea level and triggered up to 30 earthquakes per second just before erupting.

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Mount Shasta (California)

Mt Shasta looming over Highway 97 at dusk
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Located just south of the Oregon-California border, the stratovolcano Mount Shasta is also one of the tallest peaks in the Cascades, rising 14,162 feet. Over the past 10,000 years, eruptions have increased from an 800-year to a 250-year frequency. The last known eruption is thought to have occurred roughly 230 years ago.

Future eruptions like those of the last 10,000 years will probably produce deposits of ash, lava flows, domes, and pyroclastic flows, the USGS says. The flows could cause damage to low-lying areas up to 13 miles from Shasta's summit and any active satellite vents. That could include the city of Mount Shasta, which sits just on the flanks of the volcano.

What Are Pyroclastic Flows?

Pyroclastic flows are avalanches formed by hot gas, ash, lava, and other volcanic matter. They typically travel at 50 miles per hour or faster.

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Mount Hood (Oregon)

Sunset over Mount Hood and pastoral landscape
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Mount Hood, a 500,000-year-old stratovolcano located 50 miles east-southeast of Portland, last erupted in the 1790s, just before Lewis and Clark reached the Pacific Northwest. Although historically, its eruptions have been erratic, the USGS says two particular eruptions could offer perspective on future activity.

During one that occurred about 100,000 years ago, its summit and north flank collapsed, sending a lahar down the Hood River valley, across the Columbia River, and up Washington's White Salmon River valley. About 1,500 years ago, a smaller eruption produced a lahar that lifted boulders as large as eight feet wide 30 feet above the river's normal level and pushed the entire Columbia River north.

While Mount Hood may be too far from Portland to hit it with a lahar, it could dust it with rock fragments or ash, as Mount St. Helens did in 1980.

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Three Sisters (Oregon)

Three Sisters mountains in the distance at sunrise
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Oregon's Three Sisters volcanoes, also included in the Cascade Range, are commonly grouped together as one unit, but each formed at a different time from a different type of magma. Neither the North nor the Middle Sister has erupted in about 14,000 years, but the South Sister last erupted about 2,000 years ago and is considered the most likely of the three to erupt again.

The South and Middle Sisters are both recurrently active over thousands to tens of thousands of years and may erupt explosively or produce lava domes that could collapse into pyroclastic flows, the USGS says. The South Sister's most recent eruptions caused rockfall more than seven feet thick and spread a coating of ash as far as 25 miles away from the vents. A new eruption could endanger nearby communities within minutes, research suggests, with a hazard zone stretching about 12 miles in diameter.

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Akutan Peak (Alaska)

Church in front of snowy mountain in Akutan village
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Akutan Island, part of Alaska's Aleutian Arc in the Bering Sea, is home to several coastal villages and a large fish-processing facility. It's also home to Akutan Peak, a stratovolcano that rises 4,274 feet above the island.

Akutan is one of the most active volcanoes in the Aleutians and Alaska in general, with more than 20 eruptions recorded since 1790. It erupted 11 times between 1980 and 1992, and although no new eruptions have occurred since, there are ongoing hints of activity. A seismic swarm took place in 1996, for example, causing minor damage and prompting some residents and employees of the fish-processing plant to evacuate the island. There are still active fumaroles and hot springs at Akutan, and the Alaska Volcanic Observatory has reported "noteworthy seismicity" multiple times this century, including more than 100 seismic events in 2008.

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Makushin Volcano (Alaska)

Snow-covered Mount Makushin in the distance at dusk
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Southwest of Akutan is the much larger Unalaska Island, where the ice-covered Makushin Volcano is located. It stands roughly 6,000 feet tall but is broad and domelike, whereas the volcanoes surrounding it have steep-sided profiles. It shares the island with the town of Unalaska, the Aleutian Islands' main population center.

Makushin has erupted explosively many times in the last several thousand years, sometimes generating pyroclastic flows and surges. One eruption roughly 8,000 years ago had an estimated Volcanic Explosivity Index score of five. There have been many small-to-moderate eruptions at Makushin since 1786, most recently a VEI-1 in 1995. Makushin's summit caldera and eastern flanks are still speckled with high-temperature geothermal areas indicating volcanic unrest. The volcano is ranked as a "very high" threat because ash from an eruption could compromise the health of Unalaska residents and bring vital air transportation to a halt.

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Mount Spurr (Alaska)

Close-up of Mount Spurr covered in ice and snow

United States Senate / Office of Lisa Murkowski / Wikimedia Commons / Public Domain

Mount Spurr is the highest volcano in the Aleutians, standing more than 11,000 feet tall. It's located about 80 miles west of Anchorage, Alaska's most populous city. The volcano has erupted several times in the last 8,000 years, including modern eruptions in 1953 and 1992, both with VEI scores of four. Both of those eruptions came from the youngest vent of Mount Spurr, known as Crater Peak, and both deposited ash on the city of Anchorage. On top of the threat it poses to Anchorage and its population of about 300,000 people, Mount Spurr also shares many Alaskan volcanoes' potential to disrupt air travel by spewing tall ash clouds into major trans-Pacific aviation routes.

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Lassen Peak (California)

Sunset at Lassen Peak with reflection on Manzanita Lake
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The southernmost active volcano in the Cascades, Lassen Peak has one of the most massive lava domes on Earth, totaling half a cubic mile. It's the largest of more than 30 volcanic domes in Lassen Volcanic National Park to erupt in the last 300,000 years.

On May 30, 1914, Lassen woke from a 27,000-year-long siesta. It spit steam and lava for a year, leading to several explosions, avalanches, and lahars. In May 1915, it released a climactic eruption that sent ash 30,000 feet into the air and unleashed pyroclastic flows that devastated three square miles (now called "the Devastated Area"). Volcanic ash traveled as far as Winnemucca, Nevada, about 200 miles away. The outbursts continued through 1917, and steam vents were still detectable in the 1950s.

Lassen Peak is now dormant but remains active, posing a distant threat to some nearby cities such as Redding and Chico.

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Augustine Volcano (Alaska)

Aerial view of Augustine Volcano surrounded by water
Melissa Kopka / Getty Images

Alaska's Augustine Volcano forms the uninhabited Augustine Island in the southwestern Cook Inlet, which is composed almost entirely of deposits from past eruptions. It has erupted several times over the past century, notably in 1908, 1935, 1963, 1971, 1976, 1986, and 2005. The most recent featured pyroclastic flows and lahars and sent ash clouds hundreds of kilometers downwind. This explosive activity gave way to lava flows that continued for several months, until activity finally subsided in the spring of 2006.

With nearly two dozen known eruptions during the current Holocene Epoch, Augustine is the most historically active volcano in the eastern Aleutian Arc. Despite the last activity being reported in 2010, Augustine is still considered one of Alaska's most hazardous volcanoes because of its ability to potentially disrupt air traffic.

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Newberry Volcano (Oregon)

High-angle view of blue lake in Newberry National Volcanic Monument
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Oregon's Newberry Volcano covers about 617 square miles—roughly the size of Rhode Island—in the eastern Cascades, making it one of the largest volcanoes in the contiguous U.S. The shield volcano has a large summit caldera spanning 17 square miles, which contains two lakes, Paulina Lake and East Lake. The area is protected as Newberry National Volcanic Monument, located within Deschutes National Forest.

Newberry dates back at least 500,000 years, and has erupted at least 11 times since the early Holocene Epoch. Although it hasn't erupted for centuries, the USGS considers it an active volcano with a "very high" threat level, ranking it 13 among its most recent National Volcanic Threat Assessment. It's located about 20 miles south of Bend, Oregon, and any repeat of its historical eruptions could send lava flows through inhabited areas.

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Mount Baker (Washington)

View of Mount Baker at dawn across a mountain lake
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After Mount Rainier, Mount Baker is the most glaciated mountain in the Cascades, supporting more ice than all the range's other peaks (barring Rainier) combined. This means it presents many of the same mudslide dangers as Rainier, although 14,000 years of sediments show Baker to be less explosive and less active than some other Cascade mountains. It erupted several times in the 1800s and has also produced dangerous pyroclastic flows in modern times. Like lahars, these flows don't necessarily require a full-scale eruption.

Baker gave locals a scare in 1975, when it began emitting large amounts of volcanic gases, and its heat flows increased tenfold. But the feared eruption never happened. The fumarolic activity continues now, but there's no evidence it's tied to the movement of magma, which signals an eruption may be imminent.

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Glacier Peak (Washington)

Sunrise over the Glacier Peak and a reflective lake
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Glacier Peak in the Cascades is one of only two volcanoes in Washington that have generated big, explosive eruptions in the last 15,000 years (the other is, of course, Mount St. Helens). Because its magma is too viscous to flow normally from the eruptive vent, it instead blasts out at high pressure.

About 13,000 years ago, nine eruptions shot out of Glacier Peak within a few hundred years. The largest ejected more than five times more rock fragments than the 1980 Mount St. Helens eruption. As its name suggests, Glacier Peak is also heavily ice-covered and has produced severe lahars and pyroclastic flows. The volcano last erupted about 300 years ago, and because its eruptions occur several hundred to a few thousand years apart, the USGS says it's unlikely to erupt again anytime soon. Still, the peak is closely monitored, as an eruption could pose a threat to Seattle, about 70 miles away.

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Mauna Loa (Hawaii)

Overhead view of steaming, fiery vent on the Kilauea Volcano
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Hawaii's Mauna Loa, near Hilo and Holualoa, joins Mount Rainier on the U.N.'s list of Decade Volcanos. Though it may not look so big from the ground level, if you count its long submarine flanks that depress the sea floor, its summit is more than 10.5 miles above its base. Like Kilauea and other Hawaiian volcanoes, Mauna Loa erupts at a slow, oozy pace, which has formed a wide dome.

Mauna Loa's last eruption was in 1984, when the lava flow reached within four miles of Hilo, a city of 45,000. It's an especially active volcano, having erupted 33 times in recorded history—including the two largest, occurring in 1950 and 1859, and one in 1880-81 that covered land now in Hilo's city limits. Some experts suggest it's near the end of a 2,000-year cycle, with its summit lava flows poised to increase toward the northwest and southeast.

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Crater Lake (Oregon)

Island surrounded by blue water and a mountainous rim
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Oregon's Crater Lake, contained by the collapsed caldera of Mount Mazama, was formed when a series of explosive eruptions rocked the volcano about 7,000 years ago, ejecting rock as far as Canada and producing pyroclastic flows that traveled 25 miles. These events were some of the largest known eruptions during the Holocene, the current geological epoch that began about 11,500 years ago.

The most recent eruption here was about 6,600 years ago. The USGS anticipates a "very high" threat potential from a future eruption at Crater Lake. Volcanic activity could affect the nearest major city, Klamath Falls, home to about 21,000.

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Long Valley Caldera (California)

Bright blue thermal pools in the Long Valley Caldera
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About 760,000 years ago, California's Long Valley Caldera was formed by a supereruption—the USGS's term for VEI-8 eruptions—that expelled roughly 1,400 times more lava, gas, and ash than Mount St. Helens did in 1980. The caldera hasn't erupted for tens of thousands of years, although the USGS notes it "remains thermally active, with many hot springs and fumaroles, and has had significant deformation, seismicity and other unrest in recent years."

In 2018, researchers reported evidence of a large magma reservoir beneath Long Valley, holding an estimated 240 cubic miles of molten rock. That, the report noted, is enough to support another supereruption around the same size as the famed one some 760,000 years ago.