Quick Dips

Exploring Lake Taupo by Sub

Next month scientists will take the first submersible research trip beneath the waves of Lake Taupo, looking at the bottom of the lake to find out more about Taupo's violent volcanic history and to examine the geothermal system under the lakebed.

The Institute of Geological and Nuclear Sciences has gained approval for the project from the Tuwharetoa Maori Trust Board, the owner of the study area. The agreement between GNS and the board cements a joint working relationship for the project, and there is provision for closer partnerships in areas of joint interest such as environmental issues, geological hazards, and geothermal energy.

Weather permitting, the two-person German submersible will make two four-hour dives a day over four days, exploring the Horomatangi Reefs on the eastern side of the lake.

"The reefs are the site of the huge Taupo eruption of 181AD, acknowledged as the world's most violent eruption in the past 5,000 years. It produced about 50 cubic kilometres of ash and pumice and a 50km-high eruption column," project leader and minerals geologist Cornel de Ronde says.

Immediately after that eruption, the vent was plugged by solid rock. Surrounding the vent is a large area of pumice and soft sediments about three kilometres deep. The area has puzzled scientists for decades but, at 160 metres, it is one of the deepest parts of the lake, making it accessible only in a submersible.

Scientists are fairly sure the area contains an active geothermal field, including hot water jets possibly gushing out of hydrothermal "chimneys" -- the submarine equivalents of geysers like those in Rotorua. It is also possible metal-rich minerals might occur around these hydrothermal vents as they commonly do at hot-spots on the seabed off the Bay of Plenty coast and in a number of other areas worldwide.

"We will be exploring an area where no-one has ever been before, so we're unsure what we'll find, but the submersible gives us the best chance we've ever had at uncovering Taupo's deep secrets," de Ronde says.

"Our aim is to collect and analyse the fluids and gases gushing out of the submarine vents. We'll also be collecting rock and sediment samples for chemical analysis and documenting lakefloor structures with a digital video."

Results will be compared with similar analyses of seawater-dominated thermal vents near White Island, off the Bay of Plenty coast, and with on-land geothermal fields such as Wairakei. Scientists anticipate the information will help in improving the understanding of the evolution of New Zealand's geothermal fields. It should also provide new insights into the 1800-year-old Taupo eruption.

The JAGO sub has a maximum operating depth of 400 metres. Its two large acrylic windows give the crew excellent visibility and it is equipped with a large hydraulic arm for retrieving samples and manipulating objects. Typical applications include photo documentation and collection of organisms, sea-bottom surveys and environmental studies.