The three-year-old volcanic island (centre) as seen from a drone. (Photo: Sea Education Association/SEA Semester)

NASA scientists have paid their first visit to an island that rose out of the sea from the rim of the Hunga Tonga Hunga Ha'apai volcano in Tonga when it erupted in 2015.

The island, which has no official name and which NASA's Goddard Space Flight Centre researcher Dan Slayback had previously only seen from space, is nestled between two older islands in the South Pacific nation.

Mr Slayback joined scientists and students from the Sea Education Association travelling to the island by boat in early October 2018.

When they landed, they found a sticky and unexpected type of mud, plants starting to take hold that were likely seeded from bird droppings, hundreds of nesting birds — and a barn owl.

Scientists and students travelled to the island by boat in October 2018. (Photo: Dan Slayback)

"We were all like giddy schoolchildren," Mr Slayback said.

"Most of [the island] is this black gravel, I won't call it sand — pea-sized gravel," he said.

"And then there's clay washing out of the [volcano's] cone. In the satellite images, you see this light-coloured material. It's mud, this light-coloured clay mud. It's very sticky. So even though we'd seen it we didn't really know what it was, and I'm still a little baffled of where it's coming from. Because it's not ash."

NASA researcher Dan Slayback standing on the beach of the island formed by the Hunga Tonga-Hunga Ha'apai volcano. (Photo: Dan Slayback)

Plants beginning to take root in new soil

The group photographed the new vegetation growing on an isthmus connecting the island to one of its neighbours, some of it possibly growing from bird droppings.

Vegetation taking root on the flat isthmus of the new island, with the volcanic cone in the background. (Photo: Dan Slayback)

They also saw a barn owl, which probably flew over from one of the islands next door, and hundreds of nesting sooty terns in the cliffs surrounding the island's crater lake.

During his visit, Mr Slayback collected small rock samples for analysis back at NASA's labs, and tried to calculate the actual elevation of the island.

He and the students used a GPS unit to take precise location measurements, and a drone to complete an aerial survey to help make a higher-resolution 3D map of the island.

"It really surprised me how valuable it was to be there in person for some of this. It just really makes it obvious to you what is going on with the landscape," he said.

Being there in person enabled a better observation and understanding of the deep gullies running down the side of the island's cone.

"The island is eroding by rainfall much more quickly than I'd imagined," Mr Slayback said.

"We were focused on the erosion on the south coast where the waves are crashing down, which is going on. It's just that the whole island is going down, too. It's another aspect that's made very clear when you're standing in front of these huge erosion gullies," he said.

"This wasn't here three years ago, and now it's two metres deep."

The cliffs of the island's crater lake are etched with deep gullies eroded by rainfall. (Photo: Dan Slayback)

Island was never expected to last this long

When it rose up out of the Pacific Ocean in early 2015 after the Hunga Tonga Hunga Ha'apai volcano erupted, shooting rocks and lava into the sky, scientists did not expect the land mass to last.

But three years later, it is still standing — and, according to NASA, is one of only three islands formed from volcanic eruptions in the last 150 years that have survived for more than a few months.

While "there's no map of the new land", according to Mr Slayback, he and his colleagues have been watching it from satellites since its birth to try to understand why it has not yet been washed away.

Since the visit Mr Slayback has reportedly been using the data collected at the island to create a more realistic 3D model of the site.

This will help scientists better understand its volume, and how much volcanic ash and material erupted during its creation.

Mr Slayback is also said to be planning another visit to Tonga, to help answer questions about the sea floor surrounding the island.

This could help scientists to better understand why it is has so far been partially resistant to erosion — and why it has survived until now.

The island as it appeared on September 19, 2017 with the semi-transparent overlay of the area that was eroded between January 2015 and September 2017. (NASA: Cindy Starr)

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