‘The use of historical photos in conjunction with spatial technology, rather than relying on early maps and bearings, enabled us to independently infer the location of the terraces, and potentially their fate.’

Scientist and aspiring field art historian George Hook shares his story on how he applied new methodology to help pin down the location of the iconic Pink and White Terraces, lost to the world with the Mt Tarawera eruption of 1886.

A wonder lost

Recently, several research teams have sought to determine the location and fate of New Zealand’s Pink and White Terraces of Lake Rotomahana. When Otukupuarangi and Te Tarata disappeared from view in the powerful eruptions of Mt Tarawera on 10 June 1886, the country lost the ‘eighth wonder of the natural world’ – a magnificent geothermal feature that attracted numerous 19th-century tourists, including artists like Charles Blomfield and photographers such as Alfred Burton.

There were many losses on that tragic day. Along with the disappearance of the Terraces, more than 120 people perished in New Zealand’s worst volcanic disaster. Before and since the eruption, the area has been a site of spiritual and geological importance. Since 1886, the possibility of finding the Terraces has intrigued many investigators. If the locations could be determined, might it be possible to reclaim this natural wonder for future generations? So began the quest to rediscover the Terraces.

Destroyed, buried, or drowned?

The massive Rotomahana Crater excavated in the 1886 Tarawera eruption was much deeper and larger than the original lake, and much of the original shoreline and many of the lake’s geothermal features were either blasted out of existence or unrecognisable under volcanic debris. When the crater filled with water over a decade or so, the surface was also much higher as the lake’s outlook was blocked. The absence of a professionally surveyed pre-eruption topographical map therefore made it difficult for early investigators to determine where exactly the two terraces might have been located and hence their fates.

Different methods but no consensus

Since then, numerous methods have been applied to locate the missing Terraces, including early scientific surveys, comparative studies of before-and-after photographs, photogrammetry, forensic cartography, underwater surveys using remote submersibles, and the use of ground-penetrating radar and LIDAR (light detection and ranging). Despite these prolonged investigative efforts, the locations have resisted definitive inquiry, thereby inspiring or confounding researchers. Claims have been made, which have then been refuted and replaced with counter-claims, only to be further rebutted.

Consequently, there is no consensus as to whether the Terraces were lost under the lake bed, survived on land under volcanic debris, or were totally destroyed in the eruption. This all culminated recently when an 1859 field map by the Austrian geologist Ferdinand von Hochstetter and a 1959 sketch map by the Auckland physicist Ronald Keam were used by different research teams to justify conflicting claims about the fate of the Terraces: a ‘battle of the maps’ that played out in published articles (see References 1 & 2).

Investigating with PeakFinder

Intrigued by this lack of scientific consensus, our research team – geologist Dr Stephen Carey, photographer Andrew Thomas and myself – saw an opportunity for a non-map based approach that might resolve the ‘battle of the maps’, thereby helping to settle the fate of the Terraces. As I had previously used spatial technology to discover the vantage point of Antipodean landscapes by the colonial artist Eugene von Guérard (see Reference 3), we initially considered undertaking a similar study using Charles Blomfield’s pre-eruption Rotomahana paintings.

But while Blomfield’s artistic device of enhancing the height of the distant mountains and foreshortening the middle ground definitely made his paintings more sublime, it also made them unsuitable for our method of investigation as an accurate horizon line is required. While this was disappointing, we were nevertheless confident that the application of spatial technology had something to offer, so we switched our research focus to the analysis of early black and white photographs of the lake and Terraces.

Using PeakFinder in reverse

The PeakFinder application we used relies on radar data collected by Space Shuttle missions giving the height of any point on the landscape, which enables the app to generate a 360° virtual horizon from any location. The application is typically used by hikers to identify surrounding peaks, but it can also be used to determine the vantage point from which a photograph was taken. The process is somewhat time-consuming but the details are explained in our article investigating the fate of the Terraces in the latest issue of Te Papa’s journal Tuhinga (see Reference 4).

We aimed to determine the geographical coordinates of each of the Terraces by intersecting bearings to each from the located vantage points of two different pre-eruption photos. If the Terraces were found to be within the boundary of the modern lake, then the current lake level in the virtual view could be projected onto the early photographs to give an estimate of how deep beneath the lake’s surface the tops of the terraces, if still in existence, might be.

Locating a stunning pre-eruption panorama

Fortunately, we were able to assemble a 235° pre-eruption panorama of the lake’s surroundings from five photos taken by the Dunedin photographer Alfred Burton, all of which are in Te Papa’s collection. Digitally stitching together the only slightly overlapping photos provide us with an accurate visual representation of many widely spread, distant horizon landmarks.

We systematically moved PeakFinder’s virtual observer over Google Earth’s satellite view of the landscape until the profiles and positions of more distant peaks in the virtual view matched that of photographic panorama. This enabled us to accurately determine the geographical coordinates of the spot where Burton had placed his camera, which turned out to be well within the current lake.

Rotating on the spot

When we visited Lake Rotomahana to conduct our field research, the Tuhourangi Tribal Authority generously arranged for us to be taken out on a launch to that location, where we were able to replicate Burton’s panorama by taking a series of photographs as the boat rotated on the spot. The high degree of similarity between the modern and historical panoramas confirmed we had correctly located Burton’s vantage point.

Locating more bearings

The virtual panorama gave us compass bearings to the top of each Terrace, but to determine the geographical location of each, we needed to intersect the bearings from Burton’s vantage point with Terrace bearings from a pre-eruption photo taken from another location. Those bearings were acquired by conducting a similar photographic analysis of an image by Tauranga photographer Charles Spencer.

Plotting the bearings

We then marked Burton’s and Spencer’s geographical coordinates on the modern topographic map and plotted the bearings to each terrace from each photographer’s vantage point. As seen on the map below, the locations where the bearings intersect are both within the current lake.

When the current lake level is projected onto the historical photos, the top of each terrace, if still in existence, would be covered by at least 10 m of water. In fact, when those terrace locations are plotted on the bathymetric map of the lake, the water is approximately 40 m deep at each location, which raised the question of whether either terrace survived at all.

Comparing pre- and post-eruption photographs

To address the issue we compared pre- and post-eruption photos taken from close to the same spot. Given the destruction or drowning of landmarks surrounding the original lake, the profiles of more distant peaks needed to match, as they did in one pair of photos. As can been seen, most of the ridge that housed the White Terrace was no longer in existence immediately after the eruption.

We did manage to compare pre- and post-eruption photos of the Pink Terrace that suggested that some features may have survived the eruption but lie buried beneath the lake bed.

Triple confirmation

The use of historical photos in conjunction with spatial technology, rather than relying on early maps and bearings, enabled us to independently infer the location of the terraces, and potentially their fate. In terms of resolving the ‘battle of the maps’, our research findings support the contentions of both the Geological and Nuclear Sciences researchers and the National Institute of Water and Atmospheric Research scientists (see reference 5).

Using different methods, all three teams concluded that the Terrace locations are underwater but relatively close to the shoreline. Whether or not they still exist in any recognizable form remains one of the Terraces’ enduring mysteries.

For the full-length article go to Tuhinga

References:

1. Bunn, R. and Nolden, S. (2017). Forensic cartography with Hochstetter’s 1859 Pink and White Terraces survey: Te Otukapuarangi and Te Tarata. Journal of the Royal Society of New Zealand 48: 39–56.
2. de Ronde, C.E.J., Cartori Tontini, F. and Keam, R.F. (2019). Where are the Pink and White Terraces of Lake Rotomahana? Journal of the Royal Society of New Zealand 49: 35–59.
3. Hook, G. (2018). Using spatial technology to locate the view illustrated in Eugene von Guérard’s painting of the Kosciuszko massif. Proceedings of the Royal Society of Victoria 130: 18–33.
4. Hook, G. and Carey, S.P. (2018). Relocating the Pink and White Terraces of Lake Rotomahana, New Zealand: resolving the ‘battle of the maps’. Tuhinga 30: 178-208.
5. Lorrey, A. M. and Woolley, J.-M. (2018). Locating relict sinter terrace sites at Lake Rotomahana, New Zealand, with Ferdinand von Hochstetter’s legacy cartography, historic maps, and LIDAR. Frontiers in Earth Science 6 (205). doi: 10.3389/feart.2018.00205.