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50 Amazing Volcano Facts

Active today

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According to the U.S. Geological Survey, Mauna Loa's peak rises roughly 4 km above sea level, its flanks slope downward another 5 km to the ocean floor, and then it is so massive it compresses the sea floor another 8 km! (Image credit: Jacques Descloitres | MODIS)

Hawaii's Mauna Loa volcano is the world's largest active volcano, rising 13,677 feet (4,170 m) above sea level and more than 28,000 feet (8,534 m) from the deep ocean floor. It has a volume of 19,000 cubic miles (80,000 cubic kilometers).

Historic activity

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U.S. Volcanoes and NVEWS Targets: red (Image credit: USGS.)

The United States ranks third, behind Indonesia and Japan, in the number of historically active volcanoes, according to the U.S. Geological Survey.

Volcanic surface

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Basalt lava (glowing rock) oozes over basalt lava flow. Basalt is the most common rock type in the Earth's crust. (Image credit: USGS.)

More than 80 percent of the Earth's surface above and below sea level is of volcanic origin.

Close to home

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(Image credit: USGS.)

About 10 percent of the more than 1,500 volcanoes that have erupted in the past 10,000 years are located in the United States, according to the U.S. Geological Survey.

Still a threat

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Mount St. Helens dome and new growth as seen from the northwest on Oct. 27, 2004. (Image credit: USGS/David Wieprecht)

There are 65 volcanoes in the United States and its territories that scientists consider active, including Mount St. Helens.

Most destructive U.S. eruption

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By early May 19, the devastating eruption of Mount St. Helens was over. (Image credit: Photo taken on May 19 by Peter Lipman, USGS.)

The most destructive eruption in U.S. history was the May 18, 1980, eruption of Mount St. Helens.

Ash everywhere

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Ash from the May 18, 1980, eruption of Mount St. Helens blankets Connell, Wash., in June 1980. (Image credit: USGS/Lyn Topinka)

During the nine hours that Mount St. Helens erupted in 1980, the volcano spewed about 540 million tons of ash over an area of more than 22,000 square miles (57,000 square kilometers).

Landslides

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An aerial view of Mount St. Helens as seen from the northwest on Aug. 18, 1980. (Image credit: USGS/Robert Krimmel)

The Mount St. Helens eruptions caused the largest terrestrial landslide in recorded history, reducing the mountain's summit by about 1,300 feet (400 meters).

How it works

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The theory of plate tectonics is a relatively new scientific concept. (Image credit: USGS.)

The majority of Earth's volcanoes are found on the seafloor, along the mid-ocean ridge a chain of volcanic peaks that rings the planet and the spot where many of Earth's plates spread apart.

Underwater eruptions

subduction-eruption-double magma bubble 111020-02

Double magma bubble forms at Hades Vent at West Mata submarine volcano. (Image credit: Joseph Resing)

The deepest active submarine eruption seen to date is of the volcano West Mata, which lies in the Lau Basin near the islands of Fiji in the southwestern Pacific. It was detected in 2008 and occurred at a depth of 3,900 feet (1,200 meters).