Volcanology of New Zealand - Major Eruptions

Major Eruptions

New Zealand has been the site of many large explosive eruptions during the last two million years, including several of supervolcano size. These include eruptions from Macauley Island and the Taupo, Whakamaru, Mangakino, Reporoa, Rotorua, and Haroharo calderas.

Two relatively recent eruptions from the Taupo volcano are perhaps the best known. Its Oruanui eruption was the world's largest known eruption in the past 70,000 years, with a Volcanic Explosivity Index (VEI) of 8. It occurred around 26,500 years ago and deposited approximately 1,200 km³ of material. Tephra from the eruption covered much of the central North Island with ignimbrite up to 200 metres (650 feet) deep, and most of New Zealand was affected by ash fall, with even an 18 cm (7 inch) ash layer left on the Chatham Islands, 1,000 km (620 mi) away. Later erosion and sedimentation had long-lasting effects on the landscape, causing the Waikato River to shift from the Hauraki Plains to its current course through the Waikato to the Tasman Sea. New Zealand's largest lake, Lake Taupo, fills the caldera formed in this eruption.

Taupo's most recent major eruption, the Taupo or Hatepe eruption, took place around 180 CE, and is New Zealand's largest eruption since Oruanui. It ejected some 120 km³ of material (rating 7 on the VEI scale), with around 30 km³ ejected in just a few minutes. It is believed that the eruption column was 50 kilometres (31 mi) high, twice as high as the eruption column from Mount St. Helens in 1980. This makes it one of the most violent eruptions in the last 5000 years (alongside the Tianchi eruption of Baekdu at around 1000 and the 1815 eruption of Tambora). The resulting ash turned the sky red over Rome and China.

Mount Tarawera's eruption around 1310 CE, while not nearly as large, was still substantial, producing 2.5 km³ of lava and 5 km³ of tephra (VEI 5). Because its deposits, stretching from Gisborne to the Bay of Islands, were emplaced around the time that Māori permanently settled New Zealand, they have provided a useful archeological marker. Tarawera erupted again on June 10, 1886, spewing ash and debris over 16,000 km2 (6,200 sq mi), destroying the Pink and White Terraces and three villages, including Te Wairoa, and claiming the lives of perhaps 120 people. Approximately 2 km³ of tephra was erupted (VEI 5).