Such was the case earlier this month, when a small island broke through the water 11 hours after Home Reef erupted on September 10, NASA announced in a recent press release. It started around an acre, but within days grew to around 8.6 acres due to the volcano’s recent spate of eruptions, according to Tonga Geological Services, a government agency.
While the word island might conjure up images of sandy beaches and lush vegetation, that’s not quite the case with these volcanic islets.
“It’s more like a big layer of ash, steam and pumice above the ocean,” Rennie Vaiomounga, a geologist with Tonga Geological Services, told The Washington Post. This means that the new island isn’t even solid enough to walk on, although that could change if it sticks around long enough to solidify.
Eruptions in Home Reef – located in the Tonga-Kermadec subduction zone, one of the world’s most active volcanic arcs – have often produced new landmasses. But the sporadic emergence of the resulting islands is something of a “geological puzzle”, Vaiomounga said.
“We never know when the island will appear or when it will disappear,” he said.
It can take centuries, decades, or sometimes just a few years for a volcano to erupt and form an island. Home Reef’s first recorded explosion was in 1852. Five years later, it erupted again. In both cases, small islands were produced, but they were temporary. The same thing happened again in 1984 and 2006, according to the Smithsonian Institution’s Global Volcanism Program.
Each time, the small islands take on a different shape. The 1984 one — which was just over 185 acres — looked like a rectangular cheese board, with handles and all. In 2006, the island that formed looked more like an inch sticking out of the water, with the rounded mound developing cliffs at least 164 feet high.
This time around, the new island looks like an almost perfectly circular mole protruding 49 feet above the surface of the ocean. Its surface is large enough to accommodate standard 6½ football pitches.
When volcanoes erupt, the magma shatters into tiny shards of glass that shoot through the air — otherwise known as ash, Vaiomounga said. If this mixture of shattered minerals, glass and rock comes out of an underwater volcano, like the Home Reef, it drifts into the ocean.
A telltale sign of an underwater eruption is a pool of volcanic pebbles – or pumice – that leaves the surface of the water looking like a rocky beach, Vaiomounga added. Sometimes these minerals travel hundreds of miles and end up washing up on shore. But they can also accumulate and form an island.
How long the fledgling island will survive is another question. The 2006 one, for example, sank in 2008, when the volcano’s summit plunged about 33 feet under water, according to Smithsonian Institution records. The Late’iki volcano, also in Tonga, created an island that disappeared after two months in 2020. This same volcano had previously produced an island that remained for 25 years, according to NASA.
Ephemeral islands often do not live long as erosion erodes them. The minerals that turn them into islands slowly return to the seabed of their creators, who will then spew out new islands in the future – a geological circle of life, Vaiomounga said.
