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Why are there so many volcanic islands?

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In 1815, the biggest explosion in recorded history occurred during an eruption on Sumbawa island, Indonesia. It blasted 36 miles³ (151 km³) of rock dust into the atmosphere.

Most of the islands found in the oceans are, or were, volcanoes that have erupted from the ocean floor. Many of these volcanoes are part of long chains, while others form the bedrock of córa! islands. A large number are long extinct—and actually subsiding beneath the waves—but some are still spectacularly active!

The Pacific Ring of Fire

01: Ali around the Pacific, ocean floor is sinking into the hot interior of Earth at destructive piąte boundaries.

02: As one piąte is dragged beneath another, the sinking rock melts and chains of volcanoes erupt from the edge of the overlying piąte.

03: Where it plunges beneath other plates of oceanie crust, it creates island arcs such the Aleutian Islands (above) that curve across 1,550 miles (2,500 km) of ocean from Alaska to Siberia.

04: Other Pacific island arcs include the Kurii Islands and Japan, the Mariana Islands, the Philippines, Tonga, and Bougainville.

Three types of volcanic island

▲ Rift volcanoes

Ocean floors are madę of basalt rock that erupts from spreading rifts in Earth's crust called mid-ocean ridges. Some very active sections of these rifts have formed volcanic islands.

▲ Island arcs

Earth’s crust is always moving, and where two plates of oceanie crust are pushing together, one is steadily destroyed. This creates a long linę of volcanic islands along the piąte boundary.

▲ Hot spot chains

Many volcanic islands form over hot spots in the deep mantle beneath Earth’s crust. As the moving crust creeps over the hot spot, the heat forms a chain of volcanic islands.

How to: know when to leave a volcanic island

01 ■ Be aware of ground tremors and minor earthquakes. If you suddenly start noticing these on a volcanic island, then an eruption is likely.

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02 ■ Listen for ominous rumbling, humming, or buzzing—and keep an eye on animals that might have better hearing than you do. If they start behaving strangely, it might mean something!

Mont Pelee on the island of Martinique is one of many volcanoes that form an island arc in the Caribbean. In May 1902, it exploded and swamped the nearby city of Saint Pierre with red-hot rock and gas, killing morę than 30,000 people within two minutes. There were just two survivors—and