Scientists from New Zealand and the United States plan to map the bottom of Lake Rotomahana in the hope of discovering what happened to the Pink and White Terraces hydrothermal system when it was drowned soon after the 1886 Tarawera eruption.
The project is to start in late January and will be the first time in New Zealand that a lake bed has been mapped by robot-like autonomous underwater vehicles, or AUVs.
As well as producing a detailed three-dimensional map of the lake bed, the sensors on the AUVs will enable the scientists to find hydrothermal vents at the bottom of the lake.
The present-day chemistry of the lake indicates that geothermal fluids are pouring into it from below and scientists are keen to find out the number of vents on the bed, where they are, and the intensity of the venting.
The project is a collaboration involving GNS Science, the Woods Hole Oceanographic Institute (WHOI) in the United States, the University of Waikato, and the Te Arawa Lakes Trust Board.
Lake Rotomahana expanded after the eruption of Mt Tarawera in 1886, which is thought to have destroyed and drowned the Pink and White Terraces, a famed tourist attraction. What remains of the terraces is believed to be buried at the bottom of the lake.
The battery-powered AUVs will take readings of the temperature, pH levels, conductivity, depth, optical clarity and electrical potential of the water.
Scientists will use the data to form a layered map of the bed which will explain the nature of the geology and hydrothermal activity at Rotomahana.
Project leader Cornel de Ronde of GNS Science said there were 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," Dr de Ronde said.
"We also want to know what links there are between the drowned geothermal systems of Lake Rotomahana and the adjacent geothermal system at Waimangu.
"This is a rare opportunity to document the death of a land-based geothermal system and its rebirth at the bottom of a lake."
The research will also help build a computer model of the hydrothermal and magma systems beneath the lake.
Before 1886, the Pink and White Terraces were the largest silica terraces in the world and represented an enormous outflow of geothermal fluid.
Scientists believe the terraces, or their remnants, are covered by at least 50m of lake water plus an additional unknown thickness of sediment.
Lake Rotomahana is 115m deep at its deepest point.
GNS Science, with the support of the Royal Society, will be offering activities to Rotorua primary and intermediate schools in connection with this project.
Information on the activities will be sent to teachers in the Rotorua area this week.
* The Pink and White Terraces were the largest silica terraces in the world.
* They were destroyed when Mount Tarawera erupted in 1886.
* Today, they are covered by 50m of water plus a layer of sediment.
* Lake Rotomahana is 115m deep at its deepest point.
* Scientists plan to map the lake bottom to find hydrothermal vents.