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6/8/2018 — Education, Science and Technology
New research confirms fate of terraces

Researchers at GNS Science have reconfirmed work they undertook five years ago on the fate of the world famous Pink and White Terraces after the 1886 eruption of Mount Tarawera.

In a peer-reviewed paper in the Journal of The Royal Society of New Zealand published online last week, they stand by their earlier findings that the White Terraces were largely destroyed in the eruption and confirmed that remnants the Pink Terraces may lie at the bottom of Lake Rotomahana.

The paper is partly in response to recent research based on historic maps claiming that the Terraces are buried partly on land at the edge of modern Lake Rotomahana.

Lead author of the GNS Science paper, Cornel de Ronde, said an exhaustive examination of his team’s work at Lake Rotomahana between 2011 and 2014 had shown that the present-day location of the Terraces could not be buried on land, or at the edge of the Lake.

“We’ve re-examined all of our findings from several years ago and have concluded that it is untenable that the Terraces could be buried on land next to Lake Rotomahana,” Dr de Ronde said.

Findings in the just-published paper are consistent with historic photographs taken by Charles Spencer in 1881 and published maps by pioneer geologist and explorer Ferdinand von Hochstetter, who made detailed surveys and maps of the region in the 1860s.

Between 2011 and 2014, GNS Science in partnership with colleagues from Woods Hole Oceanographic Institution in the US and the University of Waikato conducted a number of investigations at Lake Rotomahana.

They collected an unprecedented amount of information to get a better understanding of the complex series of events that transformed what was an on-land geothermal system to one that was drowned after debris from the eruption of Mt Tarawera blocked the normal outflow of the lake to nearby Lake Tarawera.

Techniques used included high resolution bathymetry, magnetics, measurements of the water column, side-scan sonar, seismic surveys, underwater photography, and surveys of gas plumes and of the amount of heat entering the lake from geothermal systems under the lakefloor.

The combined power of these techniques enabled them to piece together a definitive narrative about what happened on the day of the eruption and in the weeks and months that followed.

Their research was published in 2016 as 12 peer-reviewed papers in a special issue of the high-profile Journal of Volcanology and Geothermal Research.

Their investigations were driven partly out of scientific curiosity and partly by the desire to clear up long-lasting uncertainties about the eruption and its impact on the lake and the Pink and White Terraces.

With international connections, project leader GNS Science was able to bring the latest technology and scientific heft to provide the kind of information and detail that had not been possible with previous investigations.

“The destruction of the majority of the Terraces is perhaps not surprising given that the 1886 eruption was so violent it was heard in Auckland and in the South Island. The blast left a 17 kilometres-long gash through Mt Tarawera and south-westwards beneath lake.”

After the eruption the level of the Lake rose by at least 60 metres and its area increased by about five times, drowning all the original landmarks.

Dr de Ronde said that the recent suggestion that there should be an archaeological site investigation at the edge of the Lake, including the use of ground-penetrating radar, to pinpoint the location of the Terraces would be “fruitless” as the remnants of the Terraces were at the bottom of the Lake.

Source: gns.cri.nz

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An aerial view of Lake Rotomahana with Mt Tarawera in the background. Photo: Lloyd Homer, GNS Science.
Scientists load an autonomous underwater vehicle (AUV) onto a support boat during an underwater survey of Lake Rotomahana in early 2011. Photo: Julian Thomson, GNS Science.