The Dormant Danger Deep in Lake Taupo

Ngatoro-i-rangi, the chief tohunga (priest) of the Arawa people and great navigator of the Te Arawa canoe, came to Aotearoa (New Zealand) from Hawaiki during the great migration in the 13th Century. In the Taupo region, he searched for a suitable place to settle his people. However, he was disappointed to find only a dusty basin. So Ngatoro-i-rangi plucked a large tree from the nearby Mount Tauhara and hurled it into the dusty bowl to seed a new forest. But the wind flipped the tree and it landed upside down, piercing the ground with its branches. Fresh water welled up through the holes, filling the basin and creating Taupo moana – ‘The sea of Taupo’.

Figure 1: Carvings at Mine Bay, Lake Taupo, Taupo (Photo: Sabrina Renken).
Figure 1: Carvings at Mine Bay, Lake Taupo, Taupo (Photo: Sabrina Renken).

Today, Taupo moana or Lake Taupo is situated in the centre of New Zealand’s North Island and has a surface area of 616 square kilometres, making it the largest lake in the country and second largest freshwater lake in Oceania. The lake is fed by about 30 streams, with the Tongariro, Tauranga Taupo and Waitahanui Rivers being the three dominant sources. Drainage from Lake Taupo, on the other hand, is only by the Waikato River via the Huka Falls and is one of New Zealand’s most visited tourist attractions. It’s perfect for water-skiing, sailing, and kayaking. Another honey pot is the Maori rock carvings at Mine Bay (Figure 1) that can only be seen from the water. The 10-metre-high carvings show Ngatoro-i-rangi and various Tuataras (lizards), which are believed to be Taniwhas (protectors). The two master carvers, Matahi Whakataka-Brightwell and Jonathan Randell, created this Maori art with the intention to protect Lake Taupo from the quite danger in the deep.

Figure 2: Volcanic zones of the North Island of New Zealand highlighting the Taupo Volcanic Zone (TVZ).
Figure 2: Volcanic zones of the North Island of New Zealand highlighting the Taupo Volcanic Zone (TVZ).

But the locals are not afraid of a mysterious sea serpent, but of the brute force of nature in the form of a volcano. New Zealand is positioned along the Ring of Fire and volcanism has formed most of the geographical features of the country. The modern volcanic activities of the North Island are linked to the Hikurangi Trough that marks the collision boundary or subduction zone, where the Pacific Plate is pushed under the Australian Plate. Accordingly, the Taupo Volcanic Zone (TVZ) (Figure 2) is still one of the most active zones with three frequently active volcanoes (Ruapehu, Tongariro, White Island), and two of the most productive calderas in the world (Okataina and Taupo). Thus, Lake Taupo was not created by Ngatoro-i-rangi rangi’s tree-throwing mistake, but by a sequence of volcanic eruptions of the former Taupo Volcano during the Quaternary.

Two of Taupo’s volcanic eruptions are listed among the most severe on Earth over the last 70,000 years. The Oruanui eruption happened ~26,500 years ago during the Late Pleistocene and had a Volcanic Explosivity Index (VEI) of 8. It generated ~1170 km3 of tephra (Wilson et al. 2006), causing 140 km2 of the surrounding land to collapse and form the central part of the modern caldera (Wilson, 2001). The deposited ash, rock fragments and blocks reached thicknesses of up to 200 m and 18 cm thick layers were still found around 1000 km away (Figure 3)! The subsequent Hatepe eruption was not only the second largest disaster ejected from the Taupo Volcano, but also the most recent major eruption of New Zealand dated to ~180 AD. The eruption spewed 120 km3 of volcanic materials into the atmosphere turning the sky red over Rome and China (Wilson et al, 1980). The Hatepe eruption expanded the caldera to its present day shape.

Figure 3: Main tephra spread of the Oruanui eruption (Lowe et al., 2005) and image of the Oruanui tephra layer in a bog core of the South Island (Photo: M. Vandergoes & Newnham et al., 2007).
Figure 3: Main tephra spread of the Oruanui eruption (Lowe et al., 2005) and image of the Oruanui tephra layer in a bog core of the South Island (Photo: M. Vandergoes & Newnham et al., 2007).

To set the severity of these two eruptions in a global context, the Hateoe eruption was bigger than the renowned St Helens or Pinatubo eruptions. In fact, only the Tambora eruption in Indonesia was bigger with about 160 km3 tephra ejected, but still completely dominated by the Oruanui eruption (Fig. 4).

Figure 4: Comparison of the most major volcanic eruptions over the last 70000 years. The Oruanui eruption for example threw out 1,000 times more ash than Mt St Helens (United States) did in 1980 (Image source: http://www.teara.govt.nz/).
Figure 4: Comparison of the most major volcanic eruptions over the last 70000 years. The Oruanui eruption for example threw out 1,000 times more ash than Mt St Helens (United States) did in 1980 (Image source: http://www.teara.govt.nz/).

The TVZ has been home to severe major eruptions since Homo sapiens existence and is still active. Lake Taupo is only sleeping. Today, the carving of the Ngatoro-i-rangi Polynesian settlers who arrived long after the major volcanic eruptions, has perhaps protected us…and leads me to think that behind every legend lies a hint of truth.

By Sabrina Renken, postgraduate student, Trinity College Dublin, funded by the Irish Research Scholarship Scheme 2013. During her MSc research, Sabrina studied at the University of Waikato in Hamilton, NZ, only 2 hours north of Lake Taupo.

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