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Underwater Volcanoes

How Submarine Volcanoes Support Coral Reefs

From the surface, the ocean appears as a vast and level expanse of water. But miles below lies an intricate landscape of rising mountains, steep valleys, hills, canyons and cliffs—a seascape to rival its terrestrial counterpart. And among it, thousands of volcanoes scatter the seafloor.

These submarine volcanoes, both active and extinct, are abundant along mid-ocean ridges where Earth’s tectonic plates diverge. And, though largely unseen, eruptions beneath the water’s surface can be just as volatile as those on land. If you were to listen to a volcano erupt underwater (like the one in the video below), you may hear the thunderous sound of magma escaping into the sea, muffled but still perceptible, even under thousands of feet of water.

These explosions can have repercussions on land, even the potential to generate tsunamis. But underwater volcanoes still have their redeeming qualities. In fact, they may play a crucial role in coral reef development.

When frothy magma containing gas bubbles flows from an underwater volcano and comes into contact with the water, a rapid cooling occurs, trapping pockets of air within the rock and allowing it to float. The resulting stone, called pumice, is sometimes spotted on the ocean’s surface following an undersea eruption.

Pumice can stay afloat for months, traveling thousands of miles before making landfall or becoming waterlogged and sinking to the ocean floor. Along the way, an array of organisms hitchhike their way to other parts of the ocean on these pumice rafts, colonizing new reefs and replenishing those already existing systems. Some of these pumice pieces may also wash ashore, where it’s likely their mobile species, like crabs, would disembark.

In a recent study published in PLoS One, scientists tracked some of these pieces of floating volcanic stone over a period of time. The journey began near the Pacific Island of Tonga. Aided by wind and ocean currents, the pumice traversed 3,000 miles in just eight months, carrying more than 80 species of corals, anemones, barnacles, mollusks and crabs to the coast of Australia and the Great Barrier Reef.

Organisms that otherwise would not have the capacity to make an ocean voyage are suddenly traveling thousands of miles across the sea. This dispersal of marine life over miles of ocean waters allows new species to settle and populate reef systems. Coral reefs are one of the most biologically diverse habitats in the ocean, and it turns out they may have submarine volcanoes to thank.


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