The volcanism of New Zealand has been responsible for many of the country's geographical features, especially in the North Island and the country's outlying islands. While the land's volcanism dates back to before the Zealandia microcontinent rifted away from Gondwana 60–130 million years ago, activity continues today with minor eruptions occurring every few years. This recent activity is primarily due to the country's position on the boundary between the Indo-Australian and Pacific Plates, a part of the Pacific Ring of Fire, and particularly the subduction of the Pacific Plate under the Indo-Australian Plate. New Zealand's rocks record examples of almost every kind of volcanism observed on Earth, including some of the world's largest eruptions in geologically recent times. None of the South Island's volcanoes are active.
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 Taupō, Whakamaru, Mangakino, Reporoa, Rotorua, and Haroharo calderas. Two relatively recent eruptions from the Taupō 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 Taupō, fills the caldera formed in this eruption. Taupō's most recent major eruption, the Taupō or Hatepe eruption, took place around 232 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 archaeological marker. Tarawera erupted again on 10 June 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).
Hazards As well as the direct effects of explosions, lava, and pyroclastic flows, volcanoes pose various hazards to the New Zealand populace. These include tsunamis, break-out floods and lahars from volcanically dammed lakes, ashfall, and other far field effects.
For instance, the Tangiwai disaster occurred on 24 December 1953 when the Tangiwai railway bridge across the Whangaehu River collapsed from a lahar in full flood, just before an express train was about to cross it. The train could not stop in time, and 151 people died. This was ultimately caused by Ruapehu's 1945 eruption, which had emptied the crater lake and dammed the outlet with tephra. An eruption of the Whakaari / White Island stratovolcano occurred on 8 December 2019 while there was a group of 47 visitors on the island. Twenty-two people died, either in the explosion or from injuries sustained, including two whose bodies were never found and were later declared dead. A further 25 people suffered injuries, with the majority needing intensive care for severe burns. Effects can be widespread even for eruptions of only moderate size. Ash plumes from Ruapehu's 1996 eruption forced the closure of eleven airports, including Auckland International Airport. Insurance against volcanic damage (along with other natural disasters) is provided by the country's Natural Hazards Commission.
Cultural references
The Māori had many myths and legends regarding the land's volcanic mountains. Perhaps the most well known regards the relative locations of Taranaki, Tongariro and Pihanga. It holds that the two first-named volcanoes competed for the love of the beautiful Pihanga and, after Tongariro succeeded, the defeated Taranaki moved to its lonely location near New Plymouth.
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