An unmanned, remotely piloted underwater surveillance vessel sent to observe the impact of the Hunga-Tonga Hunga-Ha'apai eruption in Tonga has returned with evidence of ongoing volcanic activity inside the crater.
Sea-Kit International’s “uncrewed surface vessel” USV Maxlimer was dispatched in June, and has brought home a plethora of data and photos to fill important gaps in our understanding of the site and surrounding ocean.
“Early data shows ongoing activity within the caldera, though it is too early to tell if it is due to continuing eruption but at a reduced intensity, or hydrothermal venting driven by cooling lava, or both,” said oceanographer Sharon Walker, from the United States’ National Oceanic and Atmospheric Administration.
This was the second phase of a voyage to study the aftermath of the volcano, which erupted on January 15, causing a tsunami which devastated parts of Tonga. The first phase took place in April, with a manned vessel finding, surprisingly, the volcano was largely intact.
The 12-metre Maxlimer, remotely controlled 16,000 kilometres away from Essex, United Kingdom, could acoustically measure depth and the state of the seabed, and send sensors down 300 metres to directly analyse the water.
It will return to the caldera this week for a more detailed survey, and map areas where telecommunications cables were damaged.
Dr Mike Williams, Niwa’s chief scientist for oceans, said the primary objective was to map the caldera and the hydrothermal vents within it.
“It is incredibly exciting to be able to look down into the caldera and see volcanic plumes. We now know that at its deepest point it is around 850 metres deep, so more than the height of 2½ Eiffel Towers.
“The data and imagery that Maxlimer has brought back is astounding and is helping us to see how the volcano has changed since the eruption.”
A team of four operators work shifts for its round-the-clock operation, and surveyors and scientists based in Australia, Egypt, Ireland, Mauritius, New Zealand, Poland and the United States are collaboratively reviewing the data.
Sea-Kit chief executive Ben Simpson said the project demonstrated the importance of this technology in reaching places which were challenging or unsafe for people.
Maxlimer experienced 3-metre seas on its return, and made the journey on less than 2% of the fuel of a typical survey vessel, he said.
Knowledge gained from the project would be invaluable to the Tongan authorities in preparing and planning for future possible eruptions.