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20 Most Dangerous Volcanoes in the U.S.

The U.S. is home to 161 active volcanoes, any one of which could erupt at any time.

20 Most Dangerous Volcanoes in the U.S.
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When the volcano on New Zealand's White Island blew up on December 9, 2019, 17 people were killed. A dozen people still remain in hospitals being treated for burns suffered when steam and molten rock exploded out of the volcano. Could the same thing happen in the U.S.?

Currently, there are 161 active volcanoes in the U.S., and the U.S. Geological Survey (U.S.G.S.) keeps tabs on them in a National Volcanic Threat Assessment. The risk a volcano poses depends on its location and eruptive style, and the U.S.G.S. list assesses which volcanoes warrant the greatest risk-mitigation efforts.

Below are the 20 most active volcanoes in the U.S., the ones that you should be keeping your eye on.

20. Iliamna Volcano - Alaska

U.S.G.S Threat Score: 115 Aviation Threat: 34.

Mount Iliamna
Mount Iliamna, Source: NPS/Buck Mangipane/Wikimedia Commons

Lying 134 miles (215 km) southwest of Anchorage, Alaska, Mount Iliamna is a 10,016-foot (3,053 m) high glacier-covered volcano in the Aleutian Range. It is known to have erupted in 5,050 BCE, 2,050 BCE, and 450 BCE and in 1650 CE, 1867 CE, and 1876 CE.

Mount Iliamna produces an almost constant plume of steam and sulfurous gases, and earthquake swarms were detected on the mountain in 1996-97 and in 2011-13.

19. Mount Okmok - Alaska

U.S.G.S Threat Score: 117. Aviation Threat: 47.

Mount Okmok
Mount Okmok, Source: USGS/Wikimedia Commons

Mount Okmok sits on Umnak Island in the eastern Aleutian Islands. The 5.8 mile (9.3 km) wide circular crater, or caldera, was once filled by a crater lake which had a depth of 500 feet (150 m).  Okmok erupted 8,300 and 2,400 years ago, and again on July 12, 2008, when it shot a plume of ash 50,000 feet (15,000 m) into the sky.

That eruption continued for five and a half days and created an 800-feet-high cone. Huge volcanic mudflows, or lahars, ran all the way from the caldera to the sea coast.

18. Long Valley Caldera - California

U.S.G.S Threat Score: 129. Aviation Threat: 29.

Long Valley Caldera
Long Valley Caldera, Source: BLM/Wikimedia Commons

Adjacent to Mammoth Mountain, Long Valley Caldera is one of Earth's largest calderas. It measures 20 miles (32 km) east-west, 11 miles (18 km) north-south, and is 3,000 feet (910 m) deep.

RELATED: THE HARM FROM VOLCANOES LASTS LONG AFTER THEY ERUPT

In May 1980, four magnitude 6 earthquakes struck the southern margin of the Long Valley Caldera, and the caldera floor lifted by 10 inches (250 mm). Since 1980, there have been earthquake swarms, uplift, changes in thermal springs and gas emissions.

In April 2006, three members of the Mammoth Mountain Ski Area ski patrol died from suffocation by carbon dioxide when they fell into a fumarole, or steam vent, on the mountain.

17. Crater Lake, Oregon

U.S.G.S Threat Score: 129. Aviation Threat: 37.

Crater Lake
Crater Lake, Source: WolfmanSF/Wikimedia Commons

Located in south-central Oregon, 60 miles (97 km) northwest of Klamath Falls, and about 80 miles (130 km) northeast of Medford lies Crater Lake. At 1,949 feet (594 m) deep, it is the deepest lake in the United States. The lake formed after the massive volcanic eruption of Mount Mazama 7,700 (± 150) years ago.

The eruption blasted out 12 cubic miles (50 cubic kilometers) of earth.

16. Mauna Loa - Hawaii

U.S.G.S Threat Score: 131. Aviation Threat: 4.

Mauna Loa
Mauna Loa, Source: Kaleodu/Wikimedia Commons

Mauna Loa is the largest active volcano on Earth. It covers half of the Island of Hawaii, and last erupted in 1984 when lava flowed to within 4.5 miles of Hilo, the island's largest population center. Eruptions in 1926 and 1950 destroyed villages and the city of Hilo is built on lava flows from eruptions during the late 19th century.

Mauna Loa has been erupting for 700,000 years, and it only emerged above sea level 400,000 years ago. Its magma comes from the Hawaii hotspot which created the Hawaiian island chain. The movement of the Pacific Tectonic Plate will carry Mauna Loa away from the hotspot between 500,000 and 1 million years from now, Mauna Loa will become extinct.

15. Glacier Peak - Washington

U.S.G.S Threat Score: 135. Aviation Threat: 37.

Glacier Peak
Glacier Peak, Source: Walter Siegmund/Wikimedia Commons

Glacier Peak is the fourth tallest peak in Washington state and is located in Snohomish County, only 70 miles (110 km) northeast of downtown Seattle.

Glacier Peak has erupted five times in the past 3,000 years. It erupted in 3,550 BCE, 3,150 BCE, 850 BCE, 200 CE (± 50 years) 900 CE (± 50 years), 1,300 CE (± 300 years), and 1,700 CE (± 100 years). 13,000 years ago, a series of eruptions produced pyroclastic flows which mixed with snow, ice, and water, forming lahars. These filled the North Fork of the Stillaguamish River and the Skagit River.

A study in 2005 by the U.S.G.S. identified Glacier Peak as one of nine Cascade volcanoes that are "very-high-threat volcanoes with inadequate monitoring".

14. Mount Baker, Washington

U.S.G.S Threat Score: 139. Aviation Threat: 15.

Mount Baker
Mount Baker, Source: Lhb1239/Wikimedia Commons

Mount Baker lies about 30 miles (48 km) due east of the city of Bellingham, Washington in the North Cascade Range. It sits at an elevation of 10,781 ft (3,286 m), and is the second-most thermally active crater in the Cascade Range, after Mount Saint Helens.

Hundreds of fumaroles on the mountain vent gases, primarily water vapor, carbon dioxide, and hydrogen sulfide. An eruption 6,600 years ago laid down a layer of ash that extended more than 40 miles (64 km) to the east. In 1891, a lahar of 3.6 cubic miles (15 cubic km) covered 1 square mile (2.6 sq km).

In March 1975, heat coming from the volcano increased tenfold, and authorities closed public access to the Baker Lake recreation area.

13. Newberry Volcano - Oregon

U.S.G.S. Threat Score: 146. Aviation Threat: 30.

Newberry Volcano
Newberry Volcano, Source: USGS/Wikimedia Commons

Located 20 miles (32 km) south of Bend, Oregon, Newberry Volcano is a large volcano. It is 75 miles (121 km) from north to south, 27 miles (43 km) east to west, and has more than 400 vents, the most of any volcano in the contiguous U.S.

Newberry began erupting 600,000 years ago, and the last eruption took place 1,300 years ago. Today, the volcano lies within 19 miles (31 km) of 16,400 people, and within 62 miles (100 km) of nearly 200,000 people, and any eruption with lava flows, pyroclastic flows, lahars, ashfall, earthquakes, avalanches, and floods would pose a significant threat to life.

12. Augustine Volcano - Alaska

U.S.G.S. Threat Score: 151. Aviation Threat: 48.

Augustine Volcano
Augustine Volcano, Source: Game McGimsey/Wikimedia Commons

Augustine Volcano forms Augustine Island, which has an area of 32.4 square miles (83.9 sq km) and is located in southwestern Cook Inlet in the Kenai Peninsula. Located 174 miles (280 km) southwest of Anchorage, Augustine Volcano is 7.5 miles (12 km) east-west, 6.2 miles (10 km) north-south, and has a height of 4,134 feet (1,260 m).

Augustine has erupted in 1883, 1935, 1963–64, 1976, 1986, and 2006. Minor eruptions occurred in 1812, 1885, 1908, 1944, and 1971. March 27, 1986, eruption left ash on Anchorage and disrupted air traffic. In April 2005, a new eruption began which continued through March 2006, with an explosion occurring on January 11, 2006.

11. Lassen Volcano - California

U.S.G.S. Threat Score: 153. Aviation Threat: 32.

Lassen Volcano
Lassen Volcano, Source: Dicklyon/Wikimedia Commons

Lassen Volcano sits at an elevation of 10,457 feet (3,187 m) above the northern Sacramento Valley. Its lava dome has a volume of 0.6 cubic miles (2.5 cu km), making it the largest lava dome on Earth. Lassen underwent at least one explosive eruption, which created a summit crater 360 feet (110 m) in-depth and having a diameter of 1,000 feet (300 m).

In May 1914, Lassen became volcanically active after 27,000 years of dormancy. A column of volcanic ash and gas was spewed more than 30,000 feet (9,100 m) high, and when the column collapsed into a pyroclastic flow, it destroyed 3 square miles (7.8 km2) of land and spawned a lahar that extended 15 miles (24 km) from the volcano.

Both the National Park Service and the U.S. Geological Survey actively monitor Lassen's fumaroles, hot springs, and mudpots. Recent surveys showed that Lassen, along with three other Cascade volcanoes, is undergoing subsidence, with the ground at Lassen Peak sinking 0.39 inches (10 mm) each year.

10. Mount Spurr - Alaska

U.S.G.S. Threat Score: 160. Aviation Threat: 48.

Mount Spurr
Mount Spurr, Source: USGS/Wikimedia Commons

Mount Spurr lies 81 miles west of Anchorage and is the highest volcano of the Aleutian arc. It is a 3-mile (5 km) wide caldera that is open to the south. 

Spurr erupted in 1953 and 1992, and in July 2004, Mount Spurr had an increasing number of earthquakes. In August 2004, a heating event melted snow and ice and created a small crater lake. By 2005, overflights revealed that the water in this lake had drained away.

Mount Spurr lies along major trans-Pacific aviation routes, and its eruption could significantly disrupt air travel, with ash clogging jet engines.

9. Makushin Volcano - Alaska

U.S.G.S. Threat Score: 161. Aviation Threat: 47.

Makushin Volcano
Makushin Volcano, Source: Wikimedia Commons

Located on Unalaska Island in the Aleutian chain, Makushin sits at an elevation of 6,680 ft (2,036 m). Its caldera is 1.6 miles (2.5 km) by 1.9 miles (3 km).

Over the last several thousand years, Makushin has erupted over two dozen times, the last time in 1995. During that eruption, which occurred on January 30, 1995, ash was sent to an altitude of 1.5 miles (2.5 km).

The closest towns to Makushin are Unalaska and Dutch Harbor, and studies have shown that tapping the geothermal reservoir beneath the volcano could provide electrical power to both towns.

8. Akutan Volcano - Alaska

U.S.G.S. Threat Score: 161. Aviation Threat: 47.

Akutan Island
Akutan Volcano, Source: Cyrus Read/Alaska Volcano Observatory/U.S.G.S.

Akutan Peak in the Aleutian Islands has an elevation of 4,275 feet (1,303 m), and its 1.25 mile (2 km) wide caldera was formed during an eruption that occurred 1,600 years ago.

The Alaska Volcano Observatory has recorded 33 eruptions at Akutan, giving it the title of the most eruptions in Alaska. The volcano last erupted in 1992, however, in March 1996, an earthquake swarm was followed by a rise on the western side and a lowering of the eastern side of the volcano.

7. Three Sisters - Oregon

U.S.G.S. Threat Score: 165. Aviation Threat: 30.

Three Sisters
Three Sisters Source: USGS/Wikimedia Commons

The three peaks, known as North Sister, Middle Sister, and South Sister, are each over 10,000 feet (3,000 m) high. Neither North Sister nor Middle Sister has erupted in the last 14,000 years and most likely will never erupt again, however, South Sister last erupted 2,000 years ago and still poses a threat.

Should South Sister erupt, it would cover the city of Bend, Oregon 22.7 miles (36.5 km) away, with ash to a depth of 1 to 2 inches (25 to 51 mm) and the volcano could unleash pyroclastic flows and mudflows.

During the 2000s, South Sister experienced an uplift of 11 inches (28 cm), but an earthquake swarm in 2004 caused the uplift to stop.

6. Mount Hood - Oregon

U.S.G.S. Threat Score: 178. Aviation Threat: 30.

Mount Hood
Mount Hood, Source: Wikimedia Commons

Located 50 miles (80 km) southeast of Portland, Oregon, Mount Hood sits at an elevation of 11,240 feet (3,426 m) and, according to the U.S. Geological Survey (USGS), the chances of Mount Hood erupting in the next 30 years are between 3% and 7%.

There have been four major eruptions over the last 15,000 years, with the last three occurring during the last 1,800 years. The last major eruption occurred in 1781-82 and the last minor eruption occurred in August 1907.

In July 1980 and June 2002, there were several earthquake swarms on the mountain and its fumaroles and hot springs are active.

5. Mount Shasta - California 

U.S.G.S. Threat Score: 178. Aviation Threat: 39.

Mount Shasta
Mount Shasta, Source: Ewen Denney/Wikimedia Commons

Sitting at 14,179 feet (4,322 m), the mountain consists of four overlapping dormant volcanic cones. Over the last 4,500 years, Mount Shasta has erupted every 600 years and deposits from these eruptions can be found under neighboring towns.

The last eruption of Mount Shasta is thought to have occurred around 1,250 CE, but should the mountain erupt again, the towns of Shasta Lake, Redding, and Anderson, California, along with Ashland, Oregon, would be subjected to volcanic ash, pyroclastic flows, lava, and lahars.

4. Redoubt Volcano - Alaska

U.S.G.S. Threat Score: 201. Aviation Threat: 48.

Redoubt Volcano
Redoubt Volcano Source: USGS/Wikimedia Commons

Located 110 miles (180 km) southwest of Anchorage, Mount Redoubt sits at an elevation of 10,197 feet (3,108 m). It has erupted in 1902, 1966, 1989 and 2009. The 1989 eruption spewed volcanic ash up to 45,000 feet (14,000 m) and shut down the engines of KLM Flight 867, a Boeing 747 when it flew through the volcano's plume. Luckily, the pilots were able to restart the engines, and the plane landed safely in Anchorage.

The ash from that eruption blanketed an area of 7,700 square miles (20,000 sq km), and pyroclastic flows and lahars reached all the way to Cook Inlet, 22 miles (35 km) away.

On March 22, 2009, Mount Redoubt began erupting and continued erupting for several months. Ash clouds reached as high as 65,000 feet (20,000 m) and the cities of Anchorage and Valdez were coated in ash. On March 28, ash forced the closing of the Anchorage airport for over 12 hours.

Since 2009, there have been small earthquakes, gas venting, and lahars. The mountain is emitting over 10,000 metric tons of carbon dioxide and sulfur dioxide per day.

3. Mount Rainier - Washington

U.S.G.S. Threat Score: 203. Aviation Threat: 37.

Mount Ranier
Mount Rainier, Source: Stan Shebs/Wikimedia Commons

At just 59 miles (95 km) southeast of Seattle, Washington, Mount Rainier sits at an elevation of 14,411 feet (4,392 m). It is considered one of the most dangerous volcanoes in the world, and due to the large amount of glacial ice on its summit and flanks, it could produce massive lahars that could threaten the 80,000 people who live in its vicinity.

Mount Rainier is capable of producing pyroclastic flows, lava and mudflows that would destroy the communities of Enumclaw, Orting, Kent, Auburn, Puyallup, Sumner and Renton, and could cause tsunamis in both Puget Sound and Lake Washington.

Reflecting the danger that Mount Rainier poses, Pierce County, just to the south of Seattle's King County, has installed lahar warning sirens and has posted escape route signs.

2. Mount St. Helens - Washington

U.S.G.S. Threat Score: 235. Aviation Threat: 59.

Mount St. Helens
Mount St. Helens, Source: Lyn Topinka/Wikimedia Commons

Mount St. Helens is located 50 miles (80 km) northeast of Portland, Oregon, and 96 miles (154 km) south of Seattle, Washington.

During March 1980, Mount St. Helens experienced an earthquake and vented steam, and in April 1980, the north side of the mountain began to bulge. On May 18, 1980, a magnitude 5.1 earthquake triggered the collapse of the north face of the mountain, causing the largest debris avalanche in recorded history.

Magma from the volcano burst out in a pyroclastic flow that flattened trees and buildings over 230 square miles (600 sq km) and released over 1.5 million metric tons of sulfur dioxide into the atmosphere.

57 people were killed, 250 homes, 47 bridges, 15 miles (24 km) of rail lines, and 185 miles (298 km) of the highway were destroyed. The ash plume reached 16 miles (27 km) in height, and it moved eastward at 60 miles per hour (100 km per h), reaching both Idaho and Edmonton in Alberta, Canada. Lahars flowed down the Toutle and Cowlitz Rivers into the Columbia River.

The eruption reduced the mountain's height from 9,677 feet (2,950 m) to 8,363 feet (2,549 m) and left a 1-mile-wide (1.6 km) horseshoe-shaped crater. Minor eruptions continued and a new lava dome formed. On March 8, 2005, a new eruption sent a 36,000-foot-tall (11,000 m) plume of steam and ash into the sky.

1. Kilauea Volcano - Hawaii

U.S.G.S.Threat Score: 263. Aviation Threat: 48.

Kilauea Volcano
Kilauea Volcano, Source: USGS/Wikimedia Commons

Located on the Big Island of Hawaii, Kilauea only emerged from the sea about 100,000 years ago. It was created by the Hawaiian-Emperor seamount hot spot and erupted nearly continuously from 1983 to 2018.

Lava from Kilauea has destroyed the towns of Kalapana and Kaimū, and in 2018, two dozen lava vents erupted in the town of Puna, forcing the evacuation of thousands of people.

On May 17, 2018, the volcano erupted, spewing ash 30,000 feet (9,144 m) into the air. Lava destroyed Hawaii's largest natural freshwater lake, covered most of Leilani Estates and Lanipuna Gardens, and inundated the communities of Kapoho, Vacationland Hawaii and most of the Kapoho Beach Lots.

Kilauea lava
Kilauea lava, Source: USGS/Wikimedia Commons

Reaching the ocean, the lava extended the coastline nearly a mile out to sea and formed laze, which forms when lava mixes with seawater and is made up of toxic hydrochloric acid and glass particles.

In all, 716 homes were destroyed by lava. On December 5, 2018, the eruption that began in 1983 was officially declared to have ended. In June 2019, U.S.G.S. instruments indicated that Kīlauea's shallow summit magma chamber was slowly refilling.

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