Source: GNS Science
A feature is that it shows the likely locations of the once-famed Pink and White Terraces, which were largely destroyed in the 1886 eruption of Mount Tarawera.
Local government and iwi groups have given the map – produced as a colourful wall poster – the thumbs up.
It is the first new bathymetric map of the lake in 40 years and represents nearly a decade of data gathering by GNS Science and its American partners.
Its resolution is 400 times better than the previous map which means it shows many geological features not seen before.
It 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 map is significant in that it locates the sites of Ōtūkapuarangi (The Pink Terrace) and Te Tarata (The White Terrace),
“The new map helps put all existing information about the 1886 Mount Tarawera eruption and the geothermal systems under Lake Rotomahana into a much better context,” said project leader Cornel de Ronde of GNS Science.
“It shows lakefloor features and other subtleties that have not been seen for more than a century, before the lake started to fill up immediately after the 1886 eruption.
“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 lakefloor topography, or bathymetry. To delve even deeper into the 6km by 3km lake, the scientists used a seismic reflection technique to effectively ‘strip off’ the recent sediments deposited into the lake, and reveal the surface of the lakefloor immediately after the eruption.
They also made measurements of magnetic and heatflow anomalies which show the distribution of different rock types, where hydrothermal fluids would have upwelled in the area prior to 1886, and where hot water is being discharged into the lake today.
These are shown in separate sidebar maps, along with a map showing several hundred locations where plumes of gas bubbles have been recorded.
The lake increased five times its original size after the 1886 eruption, which covered the surrounding countryside in mud and ash up to 40m thick. The blast was so violent, it could be heard as far away as Auckland and Christchurch.
Post-Treaty-settlement iwi governance entities Tūhourangi and Ngāti Rangitihi say they are “thrilled” with the new map and what it depicts.
“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.
Bay of Plenty Regional Council, which has supported GNS Science in bathymetric and geophysical surveys of Rotorua lakes, has also given the map its seal of approval.
“The information GNS Science portrays in its Lake Rotomahana poster will not only elevate our understanding of geological and geothermal processes in the area, but it also provides a platform for greater understanding of lake dynamics,” Senior Environmental Scientist Paul Scholes said.
The Council is providing support for the production of future maps in the Rotorua Lakes series.
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.
PDF version here: https://doi.org/10.21420/E4FK-8P15
Print copy here: https://shop.gns.cri.nz/rl-rotomahana/