They were once called the eighth wonder of the world
Until the late 19th century, New Zealand’s Pink and White Terraces along Lake Rotomahana on the North Island, attracted tourists from around the world interested in seeing the beautiful natural formations created by a large geothermal system. But the eruption of Mt Tarawera on 10 June 1886 buried the terraces in sediment and caused the lake basin to enlarge, engulfing the land where the terraces stood. For more than a century, people have speculated whether any part of the Pink and White Terraces survived
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. Scientists mapped the bottom of Lake Rotomahana and the seismic data showed a 40-metre-wide and three-storey-high stack of very hard material exactly where the Pink Terraces are estimated to be.
‘We believe this represents a substantial portion of the Pink Terraces, although we were not able to determine their state of preservation. We were unable to image individual terraces. ‘Said project leader Cornel de Ronde, of GNS Science who also said the team was elated by the discovery.
Side-scan sonar and bathymetric data collected by two REMUS 100 AUVs clearly show crescent-shaped terraced structures in about 60 metres of water where the Pink Terraces were located prior to 1886. They are covered by a brownish lake sediment.
Using new software, which became available after the data collection phase of the project had finished, the scientists later found the sonar data contained images of hard, crescent-shaped structures on the lake bed in a similar location to where the White Terraces were before the eruption. The structures are at roughly 60m depth – a similar depth to the Pink Terraces which were found in January 2011. The lake is about 122m deep at its deepest point.
Their discovery provides much greater insight into the sequence of events that made up the 1886 eruption. In particular, the data shows the volcanic craters and the deep rift that formed when the lake floor unzipped violently during the eruption. There are very few examples of large land-based geothermal systems that have been torn apart by an eruption and become inundated in this way. Scientists hope the data collected during this expedition will help them better understand how geothermal systems respond to disruptions of this kind.
‘It was very gratifying to take the tools and knowledge we’ve developed for ocean research and apply them to work in the lake, especially for a scientific project with so much Maori cultural significance.’ said Dr de Ronde who also acknowledged the permission and support from the Te Arawa Lakes Trust Board and tourism operator Waimangu Volcanic Valley, which helped with access to Lake Rotomahana.