The Tonga underwater volcano that produced a massive eruption earlier this year remains intact, New Zealand scientists said.
The eruption in January was the biggest explosion ever recorded by modern sensors.
It was so powerful, the force lifted cloud over the United Kingdom 16,500km away and generated small tsunamis in the Mediterranean Sea.
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But structurally, the underwater volcano at Hunga-Tonga Hunga-Ha'apai hasn't changed that much, research published this week showed.
Experts from New Zealand's National Institute for Water and Atmospheric (NIWA) said the new findings were "surprising" and "unexpected".
NIWA scientists aboard a research ship have mapped the post-eruption shape of Hunga-Tonga Hunga-Ha'apai (HTHH) and of the surrounding seabed.
Expedition leader, NIWA marine geologist Kevin Mackay, said he was astonished by what he'd seen in the sonar results.
"With an explosion that violent – the biggest ever recorded – you would expect that the whole volcano would have been obliterated, but it wasn't," he said.
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Mackay said while the volcano appeared intact, the seafloor showed some dramatic effects from the eruption.
"There is fine sandy mud and deep ash ripples as far as 50 kilometres away from the volcano, with gouged valleys and huge piles of sediment."
As well as the sonar survey, the researchers also studied the ocean ecosystem around the volcano.
While the edges of the volcano are now ridden of biological life, the scientists found only 15km away that fish and mussels were thriving.
"These surviving animal communities indicate what kind of life may repopulate HTHH," said marine biologist Malcolm Clark.
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The January 15 eruption of the undersea Hunga Tonga-Hunga Ha'apai volcano about 65km north of Tonga's capital Nukuʻalofa killed at least three people.
The volcanic eruption sent rarely observed pressure waves around the world for six days and a tsunami wave.
