Search for Pink and White Terraces

20:06, Nov 15 2010
Lake Rotomahana
BURIED WONDER? Scientists are to search Lake Rotomahana for traces of the famed Pink and White Terraces, which were promoted as a tourism wonder before vanishing during the 1886 eruption of Mt Tarawera.

Scientists are to use unmanned submarines to search a Rotorua lake for traces of the famed Pink and White Terraces, which were promoted as a tourism wonder before vanishing during the 1886 eruption of Mt Tarawera.

Two torpedo-like unmanned underwater vehicles will be used to map the bottom of Lake Rotomahana as New Zealand and American researchers map hydrothermal vents on the lake bed, about 22km southeast of Rotorua.

The lake was enlarged to its present 3km-by-6km size during the Tarawera eruption, from the Rotomahana and Rotomakariri lakes.

The pink terraces were originally on the west bank of Lake Rotomahana and the white ones were on the north side, and researchers said there was a possibility parts survived the eruption, particularly the white terraces, which were protected from the explosion by a ridge.

At the time, they were the largest silica terraces in the world and represented an enormous flow of geothermal fluid into the lake from vents on land. Now they are thought to be covered by at least 50m of lake water plus an additional sediment layer of unknown thickness.

Project leader, Cornel de Ronde of GNS Science, said there were very few examples of hydrothermal activity in freshwater lakes in the world, and even fewer had been studied in detail.

"Our aim is to determine what happened to the Pink and White Terraces hydrothermal system when it was drowned in the enlarged Lake Rotomahana soon after the 1886 eruption," said Dr de Ronde, who has also dived on seafloor hydrothermal vents in the Kermadec Arc northeast of New Zealand.

"We also want to know what links there are between the drowned geothermal systems of Lake Rotomahana and the adjacent geothermal system at Waimangu, which began after the eruption. There is strong evidence for a connection between Waimangu and Waiotapu.

"This is a rare opportunity to document the death of a land-based geothermal system and its rebirth at the bottom of a lake".

Lake Rotomahana is 115m deep at its deepest point, and the mapping will locate hydrothermal vents at the bottom of the lake, which chemists say are still gushing with geothermal fluids.

The project in January is a collaboration involving GNS Science, the Woods Hole Oceanographic Institute (WHOI) in the US, Waikato University, and the Te Arawa Lakes Trust Board.

Other measurements will record water temperature, acidity, electrical conductivity, depth, and clarity, as well as mapping the volcanic rocks beneath the lake floor and indicating the types of rock.

The scientists will map features on the lake bed as small as a suitcase, and create a computer model of the hydrothermal and magma systems beneath the lake.