Few things illustrate the dynamic and tentative nature of scientific investigations like the ongoing quest to locate the Pink and White Terraces at Lake Rotomahana. As an intriguing science mystery, the terraces have it all – worldwide fame, a recently discovered 19th century diary, sophisticated technology and puzzling photographic evidence. The quest to find the terraces also provides a fitting story about how science works – as the investigations take circuitous, contradictory and surprising investigative paths.

Background information about the terraces

In the mid-1800s, the Pink and White Terraces were considered to be the eighth wonder of the natural world. They attracted visitors from around the globe, which was an incredible feat considering the difficulty of travel to New Zealand. As well as being beautiful, the formations were the largest silica terraces in the world.

Each terrace resembled a staircase-like cluster of pools that descended into Lake Rotomahana. The White Terraces, known as Te Tarata (the tattooed rock), were the larger of the two wonders and covered about 8 hectares of land. The fan-shaped cascades dropped in a series of 50 large steps, covering a distance of about 240 metres. The Pink Terraces, known as Ō-tū-kapua-rangi (fountain of the clouded sky), covered 2 hectares and had warm, clear pools.

The terraces were in a remote inland location. Most of what we know about the terraces’ appearance comes from paintings and black and white photographs. Surprisingly, the exact location of the terraces was not publicly recorded.

Mount Tarawera erupted on 10 June 1886. Millions of tonnes of volcanic ash, mud and rubble covered the area. The original Lake Rotomahana was significantly altered. A portion of the lake floor was ejected, and the newly formed Rotomahana crater filled with water to form the current lake. It was widely believed that both terraces were destroyed.

The serendipitous nature of scientific research

In February 2011, a joint New Zealand-American initiative mapped the bottom of Lake Rotomahana. Their purpose was to investigate the extensive geothermal activity under the lake.

The project scientists were surprised when underwater scans revealed images of crescent-shaped terraced structures in about 60 metres of water. The location of the terraces corresponded to the position of the Pink Terraces prior to the eruption. They scanned the area two more times and were reasonably certain they had located the bottom two tiers of the Pink Terraces – as explained in the article Portion of Pink Terraces revealed underwater.

The team returned to Lake Rotomahana in 2012 to undertake further sonar and seismic surveying. Their seismic survey showed that a substantial portion of the Pink Terraces appeared to have survived the 1886 eruption and was sitting at the bottom of Lake Rotomahana, covered by 2 metres of sediment.

The detailed map showed ridges and other features that were originally above water and can be matched to old paintings and photographs of both the pre-eruption and post-eruption landscape.

The team did note that the cascading and scalloped shapes of the Pink Terraces had proved challenging to image as the seismic signals had been scattered by the many hard surfaces at different angles. Read about the project and the high-tech equipment they used in the article Pink and White Terraces under 2 metres of sediment.

The fate of the White Terraces was still unknown as they were in a part of the lake that was significantly disturbed by the eruption.

Nature of science

A hallmark of science is that it is subject to revision when new information is presented or when existing information is viewed in a new light.

New information, new observations and new inferences about the terraces

In 2010, research librarian Dr Sascha Nolden found Ferdinand von Hochstetter’s 1859 field diary. The New Zealand Government employed Hochstetter to make a geological survey of the new territory. He travelled to the terraces with a party of surveyors and artists. Over 28–30 April 1859, Hochstetter completed an azimuth compass survey and made sketches and other observations in his field diary.

Dr Nolden translated Hochstetter’s field notes from Hochstetter’s native German to English and, in 2016, passed the information on to researcher Rex Bunn. Using forensic cartography and reverse engineering, Bunn and Nolden reconstructed the historic Lake Rotomahana over a modern topographic map. Their findings (inferences) are that the terraces are buried on land, not in the lake. Bunn estimates he can pinpoint the locations with a margin of error of 35 metres.

In his diary, Hochstetter noted that his map was made over a large area with the use of a compass as his sole instrument. He said that he could make no pretensions to trigonometric exactness and that the map would be useful until a better and more complete map took its place.

What next for the terraces?

Bunn says the next step will be to survey the area using non-invasive ground-penetrating radar. If the imaging returns positive results, core sampling and excavation could follow. Those working on this project are volunteering their time and equipment.

Activity ideas

The Pink and White Terraces and the nature of science

Use this article, the two news articles Portion of Pink Terraces revealed underwater and Pink and White Terraces under 2 metres of sediment and other online information from Useful links (if desired) to explore the nature of science.

Suggested activities include:

Student activities The extra piece and Scrambled sentence draw parallels to aspects of the nature of science. Do one or both of the activities and discuss how they reflect/parallel the findings of the different investigations regarding the Pink and White Terraces.

Useful links

 

    Published 3 October 2017