The Taupo Volcanic Zone
The Taupo Volcanic Zone is named after Lake Taupo, the largest volcano in the zone. It extends some 350 kilometres from Mount Ruapehu and Mount Ngauruhoe at the southwestern tip, through Taupo, Rotorua and to Whakaari (or White Island). As you might expect from a volcanic zone, there are numerous active volcanoes and geothermal fields in the area. Orakei Korako lies right in the middle of this area in a geothermal zone between Taupo and Rotorua.
The zone has experienced several eruptions over time. In 1886, Mount Tarawera which lies south east of Rotorua, erupted killing over 100 people. Its three peaks each erupted and the noise was heard in Blenheim on the north of South Island. Over 2km3 of tephra was erupted which is more that was ejected from Mount St. Helens in 1980.
The Hatepe eruption in 181CE is thought to have emptied lake Taupo and and covered about 20,000km2 of land with volcanic ash and around 120km3 of material ejected. It is only know that it occured on this date because both Rome and China documented the sky turning red.
The Oruanui eruption 26,500 years ago was one of Earth's most significant events known to have occured reaching the highest classification of the volcanic explosivity index, VEI-8. This 'mega-colossal' explosion generated approximately 430km3 of pyroclastic fall deposits and the equivalent of 530km3 of magma. Tephra from the eruption covered central North Island with ignimbrite up to 200 metres deep and even the Chatham Islands, 1,000 kilometres away, was covered in 18cm of ash.
Lake Taupo partly fills the volcanic crater created by the explosion and contains 59km3 of water which, since the eruption, has been the largest lake in North Island.
Let's put this in perspective. The Westpac stadium or 'Cake Tin' is one of the largest stadia in New Zealand with 34,500 seats. You would need more than 20,000 of these to fill just one cubic kilometre.
The geothermal fields, which are basically areas with a relatively high heat temperature, have allowed New Zealand to develop geothermal power plants including the Wairakei Geothermal Power Plant in Taupo.
At Orakei Korako, the water temperature below ground exceeds 175°C and is often above 100°C when it reaches the surface. The water rises quickly through faults in the rock, carrying silica to the surface where it is deposited creating the incredible white silica sinter terraces. This process has been going on since before the Hatepe eruption. Heat loving microbes of different types grow depending on their local water temperature creating orange, brown and green mats. We also see fumaroles, mud pools and of course hydrothermal eruptions including geysers of which Orakei Korako has the most of any site in New Zealand.
