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Why do volcanoes exist? Because the surface of our Earth is moving all the time.
The Earth’s outer layer is split into plates, like a jigsaw puzzle. The plates are each about 50 miles thick. They float like rafts on a softer layer of rock. As the plates float, they bump together or move apart. When plates run into each other, one plate goes under the other. This is called subduction. When a plate sinks low enough, the rock melts and makes new magma for volcanoes. When plates move apart, magma comes up to the surface. The area where that happens is called a rift zone. The lava that erupts builds wide plains and volcanic mountains.
Other volcanoes take shape in the middle of plates. They form over places in the mantle where the magma is superhot. It’s like someone turned up the gas burner on a stove. As a plate moves over a hotspot, the magma melts through it.
One of America’s most active volcanoes is Mount St. Helens, in Washington State. Another is Kilauea, in Hawaii.
▲ There are seven major plates on Earth. The arrows show the direction each plate is moving.
Volcano Alert
Scientists at the Smithsonian Institution in Washington, D.C., keep track of volcanoes around the world. They say 1,300 of them have been active in the past 10,000 years. Most are on a narrow line called the Ring of Fire. It goes around the Pacific Ocean.
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Ten Most Active Volcanoes on Earth |
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1. Eyjafjallajökull, Iceland |
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2. Mount Vesuvius, Italy |
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3. Sakurajima, Japan |
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4. Mount Merapi, Indonesia |
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5. Mount Nyiragongo, Democratic Republic of Congo |
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6. Ulawun, Papua New Guinea |
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7. Taal, Philippines |
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8. Mauna Loa, Hawaii |
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9. Galeras, Colombia |
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10. Santa Mariá, Guatemala |
At rift zones, plates move apart. New crust forms when magma comes up to the surface.
At subduction zones, plates crash together. Parts of the crust slide down and melt.
Mantle
This is a layer of molten rock that lies deep inside the Earth. It’s 120 miles below the surface.
Oceanic Plate
This is a part of the Earth’s crust that’s under an ocean.
Hotspot
This is where magma melts through the Earth’s crust.
Continental Plate
This area of the Earth’s crust is part of a continent.
◀ Mount St. Helens in Washington State is a good example of a volcano in a subduction zone. Volcanoes at these zones often have powerful eruptions. Thick magma plugs their vents. The magma traps gases inside. Pressure builds up in the volcano. Finally, it pops the plug like a cap on a soda bottle!
