New map of Lake Rotomahana lakefloor shows likely locations of Pink and White Terrace remnants

Wednesday, 17 March 2021

A 2019 Beneath New Zealand documentary showed the search for the Pink And White Terraces.

The first map of the floor of Lake Rotomahana in 40 years includes the likely site of the remnants of the famed Pink and White Terraces, largely destroyed in the massive 1886 eruption of Mt Tarawera.

Produced by GNS Science, the map has benefited from nearly a decade of data gathering by GNS and its American partners.

“The new map helps put all existing information about the 1886 Mt Tarawera eruption and the geothermal systems under Lake Rotomahana into a much better context,” project leader Cornel de Ronde, of GNS, said.

The new GNS Science map of the lake floor of Lake Rotomahana

Before the eruption, which killed at least 120 people, Rotomahana was about 2km long by 1km wide. Now it measures about 6km by 3km, the lake level is about 60 metres higher, and it’s about 115m deep at its deepest point.

A sidebar to the new map of Lake Rotomahana, showing the likely locations of the remnants of the Pink and White Terraces

* Buried? Blasted into oblivion? Settling the mystery of the Pink and White Terraces

* GNS-led international expedition to delve into Lake Rotomahana looking for the long-lost Pink Terraces

Ō-tū-kapua-rangi me Te Tarata – The site of the Pink and White Terraces, depicted in this painting by JC Hoyte in the 1870s, prior to the eruption of Mt Tarawera in 1886, is a place of deep significance to Ngāti Rangitihi.

Ōtūkapuarangi (The Pink Terrace) and Te Tarata (The White Terrace) were the largest silica terraces the world had seen, GNS said. Powerful hydrothermal activity around the lake had been going on for a long time and the huge amount of hot silica rich water that flowed out of the ground formed the terraces.

Rotomahana map compilers Jenny Black and Cornel de Ronde of GNS Science.

It had been thought the terraces were likely destroyed by the eruption, but when two automated underwater vehicles from the Woods Hole Oceanographic Institution in the US were put into the water in 2011, parts of the terraces were rediscovered.

The new map showed lake floor features and other subtleties that had not been seen for more than a century, since before the lake started to fill up immediately after the 1886 eruption, de Ronde said.

“It also shows the likely locations of the remnants of the Pink and White Terraces, with the White Terraces largely destroyed during the 1886 eruption and the Pink Terraces having survived in part.”

Multi-beam sonar was used to provide a highly detailed view of the lake floor topography, or bathymetry. To delve even deeper, scientists used a seismic reflection technique to effectively strip off the recent sediments deposited into the lake, and reveal the surface of the lake floor immediately after the eruption.

The resolution of the new map was 400 times better than the previous map which meant it showed many geological features not seen before, GNS said.

Sidebar maps show the immediate post-eruption lake floor, the distribution of different rock types where hydrothermal fluids would have upwelled before 1886 and where hot water is entering the lake now, and several hundred locations where gas-bubble plumes have been recorded.

Post-Treaty-settlement iwi governance entities Tūhourangi and Ngāti Rangitihi said they were “thrilled” with the new map and what it showed.

“The map is significant in that it locates the sites of Ōtūkapuarangi (The Pink Terrace) and Te Tarata (The White Terrace),’’ said Rangitihi Pene, a trustee of the Tūhourangi Tribal Authority.

The new map is the first of a series of new bathymetric maps of the Rotorua lakes being developed by GNS Science, with the others to be published in the coming years.

The A1-sized map is available from the GNS Science webshop, either as downloadable PDF version at no cost, or a hard copy poster for $15 plus shipping.