18 Nov 2010 Scientists plan to search a lake in New Zealand’s volcanic region for traces of the long lost Pink and White Terraces – famed as the eighth wonder of the world before being buried by a volcanic eruption.

The scientific team will use unmanned submarines to map the bottom of Lake Rotomahana near Rotorua – in the heart of the central North Island geothermal region – in the hope of finding terrace remains that may have survived the eruption.

The largest silica terraces in the world, the famed Pink and White Terraces became a tourism wonder during the 19th century, but vanished in the 1886 eruption of Mt Tarawera.

Mapping Lake Rotomahana
In January 2011 New Zealand and American scientists will use two torpedo-like unmanned underwater vehicles to search the bottom of Lake Rotomahana and map hydrothermal vents on the lake bed.

The sets of terraces were on different parts of the lake – pink terraces on the western bank, and white terraces on the northern end – and researchers believe parts may have survived the eruption, particularly the white terraces, which were protected from the explosion by a ridge.

As well as expanding the lake and covering the terraces, the volcanic eruption buried several villages, including Te Wairoa – The Buried Village. About 150 people died in the eruption.

It’s estimated that at least 50m of lake water and an unknown thickness of sediment now cover the terraces, and scientists want to locate hydrothermal vents that are still gushing with geothermal fluids.

Hydrothermal activity
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,” he said.

Dr de Ronde 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
Lake Rotomahana is three kilometres wide and six kilometres long, and 115m at its deepest point.

When Mount Tarawera erupted – five kilometres to the north of Lake Rotomahana – it belched out hot mud, red hot boulders and clouds of black ash from a 17km rift that crossed the mountain, passed through the lake and extended beyond into the Waimangu Valley.

Lake Rotomahana’s waters rose 30m after the eruption which also created a 100m deep crater on the site of the terraces.

During the lake-bottom search, scientists will record water temperature, acidity, electrical conductivity, depth, and clarity, map and record the types of volcanic rock beneath the lake floor.

A computer model will be created to show the hydrothermal and magma systems beneath the lake.

Pink and White Terraces
The Pink and White Terraces – Otukapuarangi / fountain of the clouded sky, and Te Tarata / the tattooed rock – were New Zealand’s most famous tourist attraction in the 19th century.

Tourists made incredible journeys – some sailing for months from Europe – in the early 1880s specifically to view what was billed as the ‘eighth wonder of the world’.

The travertine terraces were formed by geothermally-heated water, containing large amounts of siliceous sinter, regularly spouting from two geysers located beside Lake Rotomahana and cascading down a hill slope.

The water left thick pink and white silica deposits that formed terraces enclosing pools of water.

The white terraces were the larger and more beautiful formation, covering three hectares and descending 30m down the hillside, while the pink terraces were where people went to bathe.

Background: Wairakei Terraces

About 90km south of the former site of the Pink and White Terraces, tourists can visit a smaller younger version – Wairakei Terraces, in the Waiora Valley near Lake Taupo.

The Wairakei Terraces have also formed from cascading silica, but in this case deposited by a man-made geyser that originates at the Wairakei geothermal power station and fed by the Alum Lakes.

The dramatic blue, pink and white pastel terraces are enhanced by wafting steam from the surrounding natural thermal waters renowned for healing powers.

Long used by Māori to soothe and heal bodies and limbs, Wairakei’s Te Kiri o Hinekai healing waters became a popular destination for international visitors in the 19th and early 20th centuries when the pools were promoted as healing spas.

The main bathing areas were closed for construction of the Wairakei geothermal power project in the 1960s, but were reinvented in the 1990s as a new visitor attraction that combined natural geothermal attributes with man-made redirection.

Fluid tapped from the field was piped so the hot silica-enriched waters could be channelled over man-made foundations to create natural silica terraces.

The Wairakei Terraces Māori Cultural experience includes self-guided and guided tours by local Māori who tell ancestral stories and explain the modern geothermal development. A marae welcome, local crafts, cultural performance and hangi meal are also part of the experience.

Three large bathing pools are under development so visitors will again be able to enjoy the natural healing waters. The pools are due to open this summer, and future plans include developing the area into a spa.