cropped SEA-KIT USV Maxlimer with logos for Tonga project_edited
cropped SEA-KIT USV Maxlimer with logos for Tonga project_edited

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cropped SEA-KIT USV Maxlimer with logos for Tonga project_edited
cropped SEA-KIT USV Maxlimer with logos for Tonga project_edited

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Tonga Eruption Seabed Mapping Project - TESMaP


In April 2022, NIWA and The Nippon Foundation announced a mission to discover the undersea impacts of the recent Tongan volcanic eruption.

Phase 1 (April/May 2022) saw NIWA scientists survey the ocean around the Hunga-Tonga Hunga-Ha'apai (HT–HH) volcano, covering thousands of square kilometres and collecting video images of the eruption’s impact from the research vessel Tangaroa. The seabed loss/gain image indicates their discoveries. Read NIWA's press release.


Phase 2 (July/August 2022) utilised SEA-KIT's Uncrewed Surface Vessel (USV) Maxlimer to conduct a month of further mapping inside the caldera.

3D map of Tonga volcano



The eruption of the Hunga-Tonga Hunga-Ha'apai (HT–HH) volcano in January 2022 was unprecedented and unexpected. It had catastrophic consequences, covering the main island of Tongatapu in carpets of toxic ash, generating a sonic boom that travelled around the globe and causing a tsunami that resulted in deaths and damage as far away as South America. It also severed both submarine fibre optic cables connecting Tonga with the world, leaving the country in a prolonged blackout. With similar volcanos around the globe, particularly along the Pacific Ring of Fire, the eruption of HT–HH highlights a risk to society from a lack of knowledge about them. This kind of research is vital to help protect people from similar natural disasters in the future, with the collective knowledge, experience and resources of the organisations involved helping to build a detailed and invaluable picture of the eruption’s aftermath.

Why a USV?

The use of USV Maxlimer as a configurable platform for a range of sensors provided a unique opportunity to safely gather data from inside the caldera for phase 2 of the project. Sensors onboard collected bathymetric data, water column backscatter data, sound velocity, conductivity, temperature, turbidity, oxidation reduction, pressure with depth and currents, all of which will develop and support understanding of the eruption’s undersea impact and ongoing activity. During the mission USV Maxlimer used less than 2% of the fuel consumption of a typical survey vessel. Deployment of a USV for this survey task inside the caldera therefore not only reduced risk to people, but also ensured that the carbon emissions for the project were significantly lower. The unmanned vessel also used innovative winch and sensor deployment capability to collect water column data down to 300m.



Survey area covered inside the caldera of HT-HH


Distance travelled by USV Maxlimer during survey ops

34 days

On operation for phase 2 of the TESMaP project

SEA-KIT USV Maxlimer returning from HT-HH caldera in Tonga

USV Maxlimer returned from her initial survey mission inside the caldera of the Hunga-Tonga Hunga-Ha'apai (HT–HH) volcano loaded with astounding data and imagery. She successfully mapped an area of over 800km² and travelled a distance of 1331 nautical miles during 34 days on operation for TESMaP, controlled remotely from our UK base over 16,000km away. Data and imagery collected by Maxlimer is helping scientists understand how the volcano has changed since its recent eruption. Multiple Conductivity Temp Depth (CTD) and Miniature Autonomous Plume Recorder (MAPR) casts were completed during the mission using the winch whilst the vessel was on the move, also known as 'tow-yos'.


It is the first time that a USV has been used for this type of task and demonstrates how the technology is pioneering new ways of understanding our oceans.

Read more about the data she collected and how it will help to fill important gaps in current understanding and knowledge of the seamount and water above it in this press release.

SEA-KIT USV Maxlimer returning from HT-HH caldera in Tonga.jpg

USV Maxlimer returning from the Hunga-Tonga Hunga-Ha’apai (HT-HH) caldera

Aerial view of the Hunga-Tonga Hunga-Ha’apai (HT-HH) volcano, showing new multibeam depth data overlaid on a satellite image of the islands (deep depths in blue, shallow depths in red)

Aerial view of HT-HH, showing new multibeam depth data overlaid on a satellite image

The Tonga Eruption Seabed Mapping Project (TESMaP) is being funded by The Nippon Foundation – the largest non-profit organisation based in Japan which, amongst other philanthropic activities, has been facilitating projects in the ocean field since 1962.  The research is also supported by The Nippon Foundation-GEBCO Seabed 2030 Project which aims to map the world’s ocean floor by 2030.