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NZDF survey shows Lake Rotorua 'hydrothermally active'

Fuseworks Media
Fuseworks Media

Initial results of a survey of Lake Rotorua by the New Zealand Defence Force indicate that the lake is hydrothermally active.

"We have found significant evidence of hydrothermal activity throughout the lake. This includes pockmarks on the lake floor and hydrothermal vents, with streams of bubbles seen in the water column," Lieutenant Commander Tim Garvan, who is leading the operation, said.

Marine geologist Cornel de Ronde, from GNS Science, said pockmarks indicated that gas was being discharged through the lake floor, while hydrothermal vents showed the release of gas and hot water.

"Examples of hydrothermal activity seen on the lake floor include smaller hydrothermal eruption craters that are likely expelling hot water, and pockmarks or circular features that are several metres in diameter and are formed as a result of gas being discharged through the lake floor," Dr de Ronde said.

"Many of them appear in a linear pattern, suggesting they may be related to underlying faults."

The bathymetric and magnetic survey, which is being conducted by members of the Royal New Zealand Navy’s Littoral Warfare Unit from 17 October to 18 November, has covered about 40 per cent of the lake floor.

Survey results will provide GNS Science with a high-resolution map of Lake Rotorua’s floor and geological features.

"The survey being conducted by the NZDF is valuable because it will provide us with a base map that shows areas of current and past hydrothermal activity, the location of hydrothermal eruption craters and the distribution of volcanic rocks within the lake," Dr de Ronde said.

"It will also show areas of acute shoaling, which are potentially hazardous to vessels and sailors.

"This work is the first step in a series of surveys that we hope will ultimately determine how much heat is being discharged through the lake floor from an underlying magma source, with the results feeding into our long-term hazards assessment of the area."

Lake Rotorua formed within a large caldera volcano that last erupted 240,000 years ago. It was last surveyed in 2005 by the University of Waikato.

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