Scientists who discovered remnants of the famed Pink Terraces have now solved the mystery of what happened to their sister formation, the White Terraces.



The find comes 125 years after the Mt Tarawera eruption that destroyed the natural wonder, once New Zealand's premier tourist attraction.



Using new software, GNS scientists were able to re-analyse the sonar data they collected from the floor of Lake Rotomahana last summer to find images of what they believe are the White Terraces.



The hard, crescent-shaped structures are around 60m deep - a similar depth to the remnants of the Pink Terraces which were found in January.

The Pink and White Terraces, two sets of cascading silica terraces separated by several hundred metres, were buried by the eruption of Mt Tarawera on June 10, 1886.

Project Leader Cornel de Ronde, of GNS Science, said the sonar images that appeared to be part of the White Terraces showed a horizontal segment of terraces more than 100 metres long.

"The two places on the lake floor where we encountered hard, up-standing crescent-shaped features correspond to the locations of the Pink and White Terraces before the Tarawera eruption," de Ronde said.



"The rounded terrace edges are standing up from the lake floor by about a metre in some places. The sonar images of both sets of terraces are strikingly similar."

During the project, a 10-day exercise using underwater robots, scientists managed to capture several colour photographs of part of the Pink Terraces.



However, they did not lower an underwater camera over the White Terraces as they were unaware of what the sonar data was showing at the time.



The fate of the remaining sections of the Pink and White Terraces is still unclear.



They might have been destroyed in the eruption. Alternatively, they could be lying under thick sediment which was impenetrable to sonar signals sent out by the two autonomous underwater vehicles (AUVs) used in the project.



However, de Ronde said finding remnants of both sets of terraces was a remarkable outcome.



"The project team was absolutely thrilled in January when we realised our AUVs had detected remnants of the Pink Terraces. Finding part of what we believe is the White Terraces as well has been surprising and very satisfying.



"It's gratifying to be part of a science project that can answer a century-old mystery about the fate of the Pink and White Terraces."

The project was a collaboration involving GNS Science, Woods Hole Oceanographic Institution in Massachusetts, Lamont-Doherty Earth Observatory at Columbia University in New York, the National Oceanic and Atmospheric Administration in Seattle, and the University of Waikato.



It was supported by the Te Arawa Lakes Trust Board and tourism operator Waimangu Volcanic Valley.