Despite the ferocity of its January eruption, Hunga-Tonga Hunga-Ha'apai is structurally intact.
Although there's clearly been a lot of ash deposition and movement of sediment, the volcano continues to stand tall.
"While the volcano appeared intact, the seafloor showed some dramatic effects of the eruption. There is fine sandy mud and deep ash ripples as far as 50km away from the volcano, with gouged valleys and huge piles of sediment."The Tangaroa in front of the two parts of the caldera rim that sit above the ocean surface
These density, or pyroclastic, flows were the major factor in generating the tsunami waves that inundated local islands, Mr Mackay told BBC News.The 1.8km-high HTHH was last surveyed in 2016. Combining the previous data with Tangaroa's new information has allowed scientists to make a "difference map".
The researchers also tested the water column for physical and chemical characteristics, including temperature, nutrients and oxygen concentration. In places, the ash-fall has had a fertilisation effect and triggered plankton blooms. But the flip side is that researchers could identify, too, zones where oxygen in the water has become depleted.
"Our initial analyses on the origin of the ash layer suggest that it is not a remnant of the January eruption, but may instead show the volcano is still venting. That is, it's actively releasing volcanic ash, albeit on a far smaller scale," she explained.The information from Maxlimer's multi-beam sonar equipment is expected to be particularly instructive. A naval ship that sailed across the caldera recently found the depth of water over the caldera had increased dramatically.
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