Volcanic Eruption Creates a New Island in the South Pacific

An underwater volcano in the South Pacific began spewing lava and gas earlier this month. Within only 11 hours, it led to the development of a new island that’s now visible from space, per NASA’s Earth Observatory.

By September 19, the island had risen about 50 feet above the water, measuring roughly 692 feet from north to south and 715 feet from east to west, according to estimates from the Tonga Geological Services.

The volcano, located in the Central Tonga Islands, is on a seafloor ridge stretching from New Zealand to Tonga that has the world’s highest density of underwater volcanoes, according to NASA. Tonga is a cluster of over 170 islands, some of which were created by volcanic eruptions, according to the Washington Post’s María Luisa Paúl.

This eruption started on September 10 on the Home Reef seamount, spewing lava into the ocean. The water cooled and solidified the lava, per IFL Science's Tom Hale. Rock fragments and ash from the eruption combined with the lava to form the island, according to Science Alert’s Carly Cassella. The island isn’t solid ground, though. “It’s more like a large layer of ash, steam and pumice over the ocean,” Rennie Vaiomounga, a geologist at the Tonga Geological Services, tells the Post.

From when it appeared just 11 hours after the eruption's start, the island quickly grew, reaching one acre on September 14 and six acres on September 20, reports CNN’s Zoe Sottile. A September 24 public notice from the Tonga Geological Services pegged the island’s surface area at 8.6 acres. While the volcano was still erupting as of Tuesday, the Tonga agency said it posed little threat to local communities, per CNN.

This isn’t the first time that Home Reef has birthed islands. Eruptions recorded in 1852, 1857, 1984 and 2006 all produced new land masses, according to NPR’s Joe Hernandez. But these islands all eventually disappeared. Waves and currents eroded the volcanic rock, per IFL Science, breaking down the young land masses. The 2006 island, for example, sank within two years, according to the Post.

The new island might face the same fate, but for now, it’s too early to tell. Though these islands usually disappear, a 2014 eruption created a land mass that has persisted and even hosts plants and nesting birds, per IFL Science.

Vaiomounga tells the Post that the creation of islands by eruptions is a “geological puzzle.”

“We never know when the island will appear or when it will disappear,” he says to the publication.

Home Reef is in the Tonga-Kermadec subduction zone, where the collision of three tectonic plates has created one of Earth’s most active volcanic arcs, per NASA.

That’s where, in January, a massive eruption of Tonga’s Hunga Tonga-Hunga Ha’apai volcano set the record for the largest volcanic blast of the 21st century. Now, scientists estimate that the enormous plume of water vapor released by that volcano raised the amount of water in the stratosphere by at least 5 percent. Since water vapor is a greenhouse gas, the extra water from that blast could warm the planet a small amount for a short period of time, scientists say.

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Will Sullivan is a science writer based in Washington, D.C. His work has appeared in Inside Science and NOVA Next.