NEW ORLEANS, LOUISIANA In December 2014, an explosion rocked the Pacific kingdom of Tonga, and an undersea volcano belched out enough ash and rock to create a whole new island lined with cliffs some 120 metres tall.
Unofficially named Hunga Tonga-Hunga Ha’apai, the new island wasn’t expected to last long. Similar volcanic islands usually erode away in a matter of months. But now, NASA scientists have announced far rosier estimates for the island’s lifespan, giving it between six and 30 years. The team unveiled their results today at the American Geophysical Union’s fall meeting in New Orleans.
Hunga Tonga-Hunga Ha’apai was born from an undersea volcano that looms nearly a mile above the surrounding seafloor. When it erupted, hot magma from deep inside Earth contacted cool water, sending ash and rock violently skyward. That debris settled around the volcano’s summit to form the new island, which sits between two older isles.
This kind of eruption is known for making islands. The Icelandic island of Surtsey was born this way in 1963, becoming the first well-studied instance in modern times. In the decades since, only a handful of islands have been born via so-called surtseyan eruptions. None have been more closely monitored than Hunga Tonga-Hunga Ha’apai, which has been photographed regularly by satellites since January 2015.
The satellite images reveal a landscape in flux. By April 2015, ocean currents had wormed their way into the island’s inner crater lake, hastening the cliffs’ retreat. The following month, a sandbar formed that slowed the water’s inland march. Meanwhile, a land bridge began forming between the island and its eastern neighbour. Now, the bridge is more than a quarter mile wide.
Using the satellite data, NASA scientists were able to estimate the island’s shifting volume. For the first six months, the island was rapidly losing mass, so the NASA team suspected it would vanish within six years. Then, the rate of loss decreased, indicating that the island was stabilising.
“If we fit all of our data to date, we get a 26- to 30-year lifetime,” Dan Slayback, a remote-sensing specialist at NASA’s Goddard Space Flight Center, said at a press briefing.
To refine these estimates, the team needed more up-close data. At one point, they worked with French citizen scientists, who sailed to the island with Tonga’s permission to collect samples on NASA's behalf. (Find out how a new island formed off the North Carolina coast in June.)
To see what was happening beneath the water’s surface, the NASA team turned to Vicki Ferrini, a scientist at the Lamont-Doherty Earth Observatory who happened to be aboard a nearby research vessel in April 2016. When bad weather fouled her team’s original research plan, she instead set course for Hunga Tonga-Hunga Ha’apai, mapping the island’s undersea terrain with sonar.
“It was fairly otherworldly [and] fairly exciting,” Ferrini said in a press briefing. “We were really charting the unknown.” Ferrini’s maps revealed that the seafloor to the island’s south levels out to a shelf, which probably helps govern how water currents flow around the island—a key factor in determining where, and how quickly, the island erodes.
But it’s still unclear exactly how long the island has to live. Surtsey, the Icelandic island, has persisted for decades because its rock hardened into a concrete-like material thanks to circulating warm water. Hunga Tonga-Hunga Ha’apai may not be so lucky.
Still, the wealth of data could help scientists studying an even more remote destination: Mars. Satellites orbiting the red planet have spotted thousands of long-dead volcanoes that resemble Hunga Tonga-Hunga Ha’apai. By closely tracking the island’s change over time, scientists may better understand how its cousins eroded in Martian waters more than a billion years ago.
“We have an eruption on Earth with an accelerated erosion because it’s in a marine environment, but on Mars, that environment may have been very ephemeral,” Jim Garvin, the chief scientist at NASA’s Goddard Space Flight Center, said at a press briefing. “By looking at these things in more detail, we can start to put time constraints on … the persistence of water, [which] is a holy grail on Mars.”
Lead Image: The Pacific island of Hunga Tonga-Hunga Ha'apa. Photo from video by NASA's Scientific Visualisation Studio