The Pink and White Terraces at Lake Rotomahana were once considered to be the 8th wonder of the natural world and attracted visitors from around the globe. As well as being beautiful, they were the largest silica terraces in the world and were created by an enormous outflow of geothermal fluid.
Sadly, in a massive eruption of Mount Tarawera on 10 June 1886, the famous terraces were destroyed and vanished.
However, in February 2011, scientists using 2 torpedo-like uncrewed underwater vehicles found part of the Pink Terraces sitting on the lake floor.
The find by the scientists, while unintentional, was not wholly surprising. It happened during a joint New Zealand-American project to map the bottom of Lake Rotomahana. The project is investigating the extensive geothermal activity under the lake, including how it evolved from an on-land geothermal system to a submerged one.
Scanning by autonomous underwater vehicles
The lake bed was scanned using 2 Remus 100 autonomous underwater vehicles (AUVs). The scans revealed images clearly showing crescent-shaped terraced structures in about 60m of water, covered by brownish lake sediment. The location of the terraces corresponds to the position of the Pink Terraces prior to the eruption and the resulting enlargement of the lake (which is now roughly 3km by 6km and 115m deep at its deepest point).
Investigating further using a specialised underwater camera, Dr Dan Fornari from the Woods Hole Oceanographic Institution in Massachusetts clearly captured photos of the terrace edges covered in lake sediments.
Project leader Cornel de Ronde of GNS Science says the team is elated. “The first sonar image gave a hint of a terraced structure so we scanned the area twice more, and we are now 95% certain we are seeing the bottom 2 tiers of the Pink Terraces.”
Dr de Ronde says the rest of the Pink Terraces were either destroyed during the eruption or are still concealed under thick sediment. The team believes there is a good chance that some of the upper Pink Terraces may have also survived but they were unable to penetrate the extensive mud covering using the side-scan sonar.
The scientists found no sign of the larger White Terraces in the part of the lake that matched their location prior to 1886. The 2 terraces were separated by several hundred metres prior to the eruption.
Dr de Ronde says the discovery puts to rest more than a century of speculation as to whether any part of the Pink and White Terraces survived the eruption. “Highlights in a science career don’t come any better than this.”
First New Zealand lake bed mapping
As well as the rediscovery of the Pink Terraces, the mapping project has been a success. It is the first time in New Zealand that a lake bed has been mapped by AUVs. The scans will produce a detailed 3-dimensional map of the lake bed. The sophisticated sensors on the AUVs enabled the scientists to locate hydrothermal vents at the bottom of the lake.
Other measurements the sensors have taken include temperaturepH, conductivity, depth, optical clarity of the water and the electrical potential (Eh) of the lake water. The AUVs also map the magnetic signature of the volcanic rocks beneath the lake floor.
The team is compiling the data into a layered map of the lake bed, which will include the geology and hydrothermal activity at Rotomahana.
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.
Read about stage 2 of the project to find out more about the Terraces and the geothermal system that created them begins in March 2012.
The eruption of Mount Tarawera in 1886 destroyed the Pink and White Terraces. Your students may like to explore this interactive activity that shows the major volcanoes in New Zealand and when they last erupted.
GNS Science has created a map of Rotomahana's lake floor. It shows floor features that have not been seen for more than a century, including the likely locations of the remnants of the Pink and White Terraces. This article from Stuff explains how the map was made. The GNS Science webshop is offering a free downloadable PDF version of the map.