The People of Taupo Lake Taupo was created by a large eruption 2000 years ago, and is according to a tribal myth, the pulsating heart of Maui's fish (New Zealand's North Island). Fed by the spirited Rivers of the Sacred Mountains this beautiful clear deep volcanic lake is the lifeforce of its surrounding land and its guardians. Attracted by the lake and thermal resources, the area was settled by Maori in the late 14th century, becoming a stronghold for the Ngati Tuwharetoa people. European visitors came to the scenic heart of the North Island in the middle of the 19th Century and settled here from about 1860. Maori Tradition relates that the great priest Ngatoroirangi and a chief, Tia, arrived in the Arawa canoe that made landfall at Cape Runaway and its people settled in the Bay of Plenty. Tia was the first to explore inland and came across the eastern side of Taupo. He noted that a formation of rock resembled his heavy cloak and hung the cloak, or taupo, on a post and claimed the area as Taupo nui a Tia, which means the Great Cloak of Tia. Ngatoroirangi arrived soon after and headed further south to the then lifeless mountains. He climbed to the top of one of the peaks and was almost overcome by the terrible cold. He called upon his sisters overseas in the ancestral home of Hawaiki to send him heat for warmth. The fire gods answered the sisters prayers and the fire came, travelling under the sea and land. At the coast of New Zealand, the fire broke through the surface as volcanic or thermal activity and ran as a line through White Island, Rotorua, Taupo and down to the mountains which erupted as volcanoes. Taupo's Volcanic History The vast and scenic Lake Taupo is not always recognised as a volcano, yet it has had a fiery and violent history. It has erupted 28 times in the past 27,000 years. Although most of these eruptions were small, the most recent -- the Taupo eruption of 181AD -- was extremely large and violent. The shape of Lake Taupo was largely created by the Oruanui eruption 26,500 years ago. This eruption formed a 500m-deep caldera (large collapsed crater) that was enlarged by the 181AD Taupo eruption. The 26,500 year-old and 181AD eruptions were extraordinarily complex and violent, and they have attracted interest from scientists internationally. The other 26 eruptions in between were small, many not much larger than a typical Mt Ruapehu eruption. 
What is a caldera volcano? There are two very different types of volcano -- cones and calderas. Cone volcanoes generate many small eruptions from the same site. An example is Mt Ruapehu which has been erupting almost continuously for about 260,000 years. The amount of ash and lava they erupt is usually between 0.001 to 0.2km3. The many frequent eruptions from cone volcanoes result in the accumulation of large volumes of volcanic debris close to the vent producing steep-sided cones like Ruapehu, Egmont, and Ngauruhoe. Caldera volcanoes such as Taupo produce larger and less frequent eruptions. Sometimes their eruptions are as large as 50km3 or even bigger, and form new caldera structures. Other eruptions are smaller and contained within the existing caldera like many of Taupo's eruptions over the past 20,000 years. These small eruptions are typically between 0.5 and 10km3. Caldera-forming eruptions drain the magma reservoir beneath the volcano, causing the ground to collapse, so that the eruption forms a depression in the earth's surface. New Zealand's two most active caldera volcanoes are Taupo and Okataina (which last erupted from Mt Tarawera in 1886, killing 108 people). All large caldera volcanoes have associated geothermal systems, where large bodies of underground water are heated by the volcano. An example is the Wairakei geothermal area, which produces about 8 percent of New Zealand's electricity. New Zealand-developed technology associated with Wairakei has been used to assist with geothermal energy developments in many countries over the past four decades. The Oruanui eruption The 26,500 year-old Oruanui eruption produced huge volumes of ash and other volcanic material that buried parts of the central North Island. Close to the vent the ash reached depths of about 100m. The size of the eruption is difficult to grasp, but roughly 800km3 of pumice and ash were ejected in this one event. The ash blanketed a huge area of ocean floor to the east of New Zealand with a layer that varied in thickness from 20cm to 1cm. Even the Chatham Islands, 800km to the east of New Zealand, received an 11cm coating. The rapid eruption of so much material caused several hundred km2 of the area around the vent to collapse to form the Lake Taupo basin, now partly filled by the lake. The 181AD Taupo eruption This eruption took place from a vent or vents near the Horomatangi Reefs, now submerged on the eastern side of Lake Taupo. The eruption lasted between several days and several weeks and produced a sequence of pumice deposits that blanketed the landscape east of Taupo. In total about 100km3 was erupted. The Taupo eruption was extremely complex, partly due to the influence of the lake water. At some stages, the eruption material was dry and fall deposits consisted of blocks of pumice and rock fragments, with no fine ash. During other stages, the eruption was ''wet'' as abundant lake water mixed into the eruption column, producing fine ash. At the climax of this eruption, about 30km3 of pumice, ash and rock fragments was erupted in only a few minutes and travelled horizontally as a liquid flow, moving at speeds estimated at between 600-900kmh. It crossed every obstacle in its path except the top of Mt Ruapehu. The 181AD Taupo eruption is unusual in several ways.- it produced an eruption column 50km high -- twice as high as the 1980 Mt St Helens eruption column.
- it was the most violent eruption in the world in the past 5000 years.
- the effects of the eruption were seen in the sky as far away as Europe and China.
- the eruption devastated an area now populated by over 200,000 people.
- if the same eruption occurred today, ashfall and other debris would cause chaos from Hamilton to Palmerston North, and buildings in Rotorua and Gisborne could be damaged or destroyed.
The challenge of the Taupo volcano Taupo volcano represents a major scientific challenge in that its activity is so variable. In the last 50,000 years, it has had eruptions that vary in volume from 0.05km3 (slightly larger than a typical Ruapehu eruption) to over 800km3. Some eruptions have been ''dry'' and formed pumice deposits, while others have been ''wet'' where lake water was mixed into the eruption column, and formed fine ash deposits. It is impossible to forecast when the next eruption will occur at Taupo, or what size it will be. The best available information shows that there is no relationship between the size of eruption and the time break between eruptions. The next eruption might be next year, or not for hundreds of years. It might produce a small lava dome, or it might destroy the central North Island as the volcano has done in the past. All that is certain, is that Taupo will erupt again. Some interesting facts about Taupo - Taupo is the most frequently active and productive rhyolite volcano in the world.
- Taupo caldera (collapsed crater) occupies about the same area as metropolitan Auckland.
- the Oruanui eruption of 26,500 years ago produced enough material to build three Ruapehu-sized cones.
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