Queenstown's Lake Wakatipu floor mapped to uncover tsunami threat

Wednesday, 8 May 2019

Researchers are conducting a search of Queenstown's Lake Wakatipu's floor for the first time to determine the potential for landslides and tsunamis.

A first-time exploration of Queenstown's Lake Wakatipu floor is hoped to reveal if a tsunami is likely.

Researchers are mapping the lake floor this week to determine the potential for landslides and tsunamis.

Marine geologist Dr Joshu Mountjoy, who is leading the project, said most people thought of tsunamis as ocean-based, but they could happen in lakes too.

'Worldwide there have been some very large lake tsunami and Wakatipu is the type of environment where these happen.'

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Lake Wakatipu had been identified as a priority due to its proximity to Queenstown, population, high-value infrastructure and the way mountains rose straight out of the lake, he said.

'I think there is a real need to understand lakes better and this offers so much opportunity … hazards are one important aspect of that.'

The 291 kilometre squared lake was New Zealand's longest and third largest lake, and sat close to one of the country's largest earthquake sources, the Alpine Fault.

'We know that New Zealand's active and dynamic landscape can really go crazy during earthquakes, think of the landslides during the 2016 Kaikōura Earthquake, so lake tsunami hazard really needs to be better understood for the resilience of New Zealand communities and infrastructure.'

The Lake Wakatipu project followed mapping of Lake Tekapo two years ago – the first time a lake floor had been mapped in New Zealand – which revealed an unexpectedly dynamic lake bed and the potential for landslide tsunami waves up to 5 metres high, Mountjoy said.

The team would use advanced multibeam echo sonar equipment to map the lake floor. Multibeam echo sounders emitted a fan of sound beams to the lake floor to scan a wide section in detail. The beams were reflected back to a receiver with the system calculating water depth from the time it took the sound to travel to the lake floor and back to the boat.

From there, sophisticated software is able to produce seamless, high-quality bathymetric maps which give an unprecedented insight into the shape of the lake floor and the processes that have shaped it.

Data would be analysed later this year.