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Friday, 10 June 2011

The White Terraces Reappear after 125 years


On 10th June 1886, exactly 125 years ago today, Mount Tarawera erupted briefly and violently, resulting in the disappearance of the Pink and White Terraces of Rotomahana, and devastation of the landscape. The former lake disappeared and was slowly replaced by the much larger and deeper lake which remains to this day.

This 1880 Charles Spencer image is  courtesy of Te Papa Museum

Last January, in a GNS Science led international expedition, Cornel de Ronde and his team rediscovered the Pink Terraces at the bottom of the  modern lake, which had been so drastically altered and deepened by the eruption. The Pink Terraces were first spotted in images from a side-scan sonar that was mounted in an autonomous underwater vehicle (AUV) used to survey the lake.

Today Cornel de Ronde announced that the White Terraces have also been found using data retrieved on the last day of the expedition, that had not been analysed until recently. When the Pink Terrace side-scans were first seen, they were nothing like anything that had been observed by the team before. An underwater camera was used to confirm that they did indeed represent the Pink Terraces. (For details of the Pink Terrace discovery watch this video).

Similar looking side scan images have now been found in the location where the White Terraces are expected to have once existed. A horizontal segment of the formations over 150 metres across may be the remains of the silica terraces along the former shoreline of the lake, now tens of metres below water level. It is not yet known whether more of the terraces lie hidden beneath volcanic mud, or whether the rest of them were forever destroyed in 1886. Future exploration may settle this question.

Ron Keam of Auckland University is an expert on the history of the Tarawera Eruption and the Rotomahana landscape. He compiled this map of the former Lake Rotomahana as accurately as possible by detailed study of  pre 1886 photographs. The Pink Terraces can be seen on the left (west) side of the lake, with the White Terraces at the top (northern) end, about a kilometre northeast of the Pinks.

The image to the right is the compiled side scan of the part of the modern lake under which the remains of the terraces lie.  The long straight lines show the path of the AUV as it progressed up and down the lake area.  The red circles show the locations of the two sets of terraces, about 1 kilometre apart. Lower left are the Pinks and upper right are the newly refound parts of White Terraces.





This close up of the side scan image  shows the curved overlapping terrace formation on the lower half below the blank, unscanned area. These features are very similar in general appearance to the photographically verified scans of the Pink Terraces found last summer.

(All sidescan images courtesy of our US project partners at the Woods Hole Oceanographic Institution)






For more details have a look at our media release, and watch the video of Cornel de Ronde describing how the discovery unfolded step by step, including the crucial hook shaped landform that first led to the location of the Pink Terraces, followed now by the Whites:

8 comments:

Anonymous said...

Would it be possible to drain lake rotomahana into lake tarawera as there is about a 40 metre difference?

Julian said...

Thanks for your question - Lake Rotomahana is about 6 kms long and up to 3 kms wide, so the environmental impact of emptying the lake would be very great. Also, the terraces are at a depth of over 40 metres (certainly the remains of the Pinks that we photographed in January) so they would still be underwater.

frank-partridge@live.com.au said...

it can be done at a very low cost and take twelve months to drain down 80 metres but up to 10 years to clean the mud off with less than 15% enviromental impact.

David Scott said...

Hi Frank, do you any more detailed information available for such a proposal? It sounds intriguing, and one could certainly imagine a scenario where the lake level is dropped and the terraces reinstated as good public relations to offset the development of the lake for geothermal power.

The environmental impact might be great, but certainly not as great as the damage that has occurred to other geothermal areas in the name of power generation. Orakei Korako and its emerald terrace for example once contained some of the largest geysers in the world but now sits 30 metres beneath the manmade Lake Ohakuri, and will most likely suffer even more damage at the hands of the new nearby geothermal station being opened in 2013.

It would certainly spark public debate if a credible plan to reinstate the terraces were proposed.

Anonymous said...

I am still a sceptic: if as you say the recent discovery would still be underwater even if the level of Lake Rotomahana was lowered by 40 metres to equal that of Lake Tarawera then whatever has been discovered cannot possibly be the famed pink terraces as claimed because the base of both terraces was the surface of the original Lake Rotomahana (described by Hochtstetter, Percy, et al as being 40 feet or 12 metres higher than Tarawera).
Unless Tarawera has risen by more than 20 metres since 1866 there is a major discrepency to be explained.
Cheers, Graeme Easte
pastfinders@clear.net.nz

Room Six St Gerards said...

We read an article in the school journal today about 'The 8th wonder of the World'. We learnt a lot and discuss the negatives and positives about the pink and white terraces being discovered. We look forward to hearing about the future for the Pink and White Terraces.

Room Six St Gerards said...

We read an article on the Pink and White terraces today with mixed reviews. We discussed the positives and negatives about the re-discovery of the terraces and what it means for local iwi and New Zealand. We look forward to learning more.

Stone said...

Is professor Kemp still going?