Unmanned vessel records continued volcanic activity deep within HTHH

Clear signs of continued volcanic activity have been observed inside the deep Hunga-Tonga Hunga-Ha’apai caldera (HTHH) volcano by an unmanned remotely operated surface vessel, the (USV) Maxlimer on his first initial fact-finding mission to Tonga.

Scientists say it’s too early to tell whether this is due to continued eruption or hydrothermal venting of cooling lava or both. They are continuing their surveys to map the caldera and the hydrothermal vents therein.

In a statement on August 3, SEACASE international said that USV Maxlimer had returned from a first fact-finding mission inside the caldera of HTHH volcano carrying important data and imagery to fill gaps in current understanding and knowledge of the seamount and the water above.

The remotely operated vessel is working on the second phase of the Tonga eruption seabed mapping project – TESMaP, funded by the Nippon Foundation.

Maxlimer was expected to return to the caldera last week for more detailed study and to better target volcanic plumes and hydrothermal vents using conductivity temperature depth (TDC) instrument and a miniature autonomous plume recorder (MAPR).

The MAPR project is a joint initiative between NOAA in the UNITED STATES and GNS Science in New Zealand.

The 12 meters USV is remotely controlled on his caldera missions since SEACASE International’s base in Essex, UK, where a team of four operators work shifts for 24-hour operation.

A global team of surveyors and scientists based in Australia, Egypt, Ireland, Mauritius, New Zealand, Poland and the UNITED STATES collaboratively monitor and review the data collected.

Sharon Walker, oceanographer at NOAAThe Pacific Ocean Marine Environment Laboratory said early data shows continued activity in the caldera, although it’s too early to tell if it’s due to a continued eruption but at reduced intensity, or to hydrothermal venting driven by cooling lava, or both.

USV Maxlimer is equipped with a multibeam echo sounder (MBES) to acoustically measure the depth and condition of the seabed. Importantly, the vessel also features a new winch capability for deploying multiple sensors up to 300 meters to obtain direct water column measurements.

Dr. Mike Williams, Chief Scientist – Oceans at NIWA said: “The primary goal of Phase 2 is to map the caldera and the hydrothermal vents within it and Maxlimer is crucial to achieving this. It’s incredibly exciting to be able to look into the caldera and see volcanic plumes.

We now know that at its deepest point it is about 850 meters deep, more than the height of two and a half Eiffel Towers. The data and images Maxlimer brought back are stunning and help us see how the volcano has changed since the eruption.

Pictured above is an aerial view of the Hunga-Tonga-Hunga-Ha’apai (excluding taxHH) volcano, showing new multibeam depth data overlaid on a satellite image of the islands (great depths in blue, shallow depths in red). Image: SEACASE / NIWA-Japanese Foundation TESMAP investigation team.

Telecommunications Cable Survey

USV Maxlimer must also map areas where telecommunications cables have been damaged as a result HTHHviolent eruption in January 2022.

During phase 1 of the project, the crew of NIWAthe research vessel, VR Tangaroa, discovered that the severed home internet cable was buried under 30 meters of ash and sediment. The project and local stakeholders hope to better understand the extent of the damage and how it was caused – likely due to rapid pyroclastic flows – from Phase 2. SEACASEit is USV can also be deployed to investigate alternative sites suitable for replacement cables if required before returning to the UK.

Ben Simpson, SEACASE CEOsaid Maxlimer was the first SEACASE Class X USV to be built and had operated in seas of three meters on the return from this first mission.

“This project clearly demonstrates how crucial this technology is as a low-risk, non-invasive solution for reaching, surveying and understanding places that are difficult or dangerous for people to reach,” he said.

The vessel uses less than 2% of the fuel of a typical survey vessel.

The knowledge gained from the project will be invaluable to Tongan authorities in preparing for and planning for possible future eruptions.


Lucy Joyce, British High Commissioner to Tonga, said: “Assessment of the Hunga-Tonga Hunga-Ha’apai caldera and the waters and seabed surrounding it is of considerable interest and importance. for all of us here in Tonga who experienced the huge explosion and tsunami in January.

The knowledge gained from the project will be invaluable to Tongan authorities in preparing for and planning for possible future eruptions.

Nippon Foundation Executive Director Mitsuyuki Unno said, “We look forward to sharing the results of this trip in the coming months and exploring ways in which the findings can benefit the people of Tonga.

Valerie J. Wallis