12/31/2023 0 Comments China frozen waterfallIt is superimposed on the present day North Island. Hatepe eruption impact of a 10-cm ash deposit (white shading) and ignimbrite from pyroclastic flow (yellow shading). It is superimposed on present day New Zealand although at the time New Zealand land mass was larger, as sea level was much lower. The central red area is the Oruanui caldera with surrounding collapse crater in lighter red. Oruanui eruption impact North Island in terms of approximate 10cm ash deposit (white shading) and approximate ignimbrite from pyroclastic flow (yellow shading). White shading is selected caldera features. Rhyolite, ( ignimbrite is lighter shades of violet), and plutonic. While Taupō has been active for about 300,000 years, explosive eruptions have been more typical in the last 42,000 years. Some of these were enormous, and two eruptions around 1.25 and 1.0 million years ago were big enough to generate an ignimbrite sheet that covered the North Island from Auckland to Napier. A key to the vents is in the diagramĮarlier ignimbrite eruptions occurred further north than Taupō. Present active geothermal systems are in light blue. Pyroclastic flows can travel hundreds of kilometres an hour.Įarlier eruptions Recent vents and caldera structures Taupō Volcano. When the pumice and ash settle, they are sufficiently hot to stick together as a rock called ignimbrite. If the material thrown out cools more rapidly and becomes denser than the air, it cannot rise as high, and suddenly collapses back to the ground, forming a pyroclastic flow, hitting the surface like water from a waterfall, and spreading sideways across the land at enormous speed. If the volcano creates a stable plume, high in the atmosphere, the pumice and ash are blown sideways, and eventually fall to the ground, draping the landscape like snow. Such eruptions tend to be earlier in any given eruption cycle. The magma froths to form pumice and ash, which is thrown out with great force. However, when mixed with gas or steam, rhyolitic eruptions can be extremely violent. If the magma does not contain much gas, rhyolite tends to just form a lava dome, and such eruptions are more common. For unknown as yet reasons, possibly associated with the present high rate of rift spreading and the recent subduction of the Hikurangi Plateau this area is very productive in its surface volcanism. Studies show large areas of partial melt below 10 km (6.2 mi) with a brittle-ductile rosk transition at approximately 6–8 km (3.7–5.0 mi) beneath the surface. In this region the Moho discontinuity starts about 25–30 km (16–19 mi) beneath the surface beyound the modern Taupō Rift boundaries to the west and east, but there is an area of strong contrast in seismic velocity at 16 kn (30 km/h 18 mph) depth that is postulated to be due to intruded crust from where the feed magma is evolving. This is an intra-arc rift in the eastern part of the continental Australian Plate, resulting from an oblique convergence with the Pacific Plate in the Hikurangi subduction zone. The Taupō Volcano erupts rhyolite, a viscous magma, with a high silica content, a feature associated with the middle portion of the Taupō Volcanic Zone within the Taupō Rift. Geologic studies published in 1888 following the eruption of Mount Tarawera first raised the possibility that there was a volcano under Lake Taupō, rather than the more obvious volcanoes near Mount Tongariro, to explain the likely source of the extensive surface pumice deposits of the central North Island. Mount Tarawera had a moderately violent VEI-5 eruption in 1886, and Whakaari/White Island is frequently active, erupting most recently in December 2019. Some volcanoes within the Taupō Volcanic Zone have erupted more recently. Taupō Volcano has not erupted for approximately 1,800 years however, with research beginning in 1979 and published in 2022, the data collated over the 42-year period shows that Taupō Volcano is active with periods of volcanic unrest and has been for some time. The Oruanui eruption in particular destroyed or obscured much evidence of previous eruptive activity. There have been many more eruptions, with major ones every thousand years or so (see timeline of last 10,000 years of eruptions). The main eruptions that still affect the surrounding landscape are the dacitic Mount Tauhara eruption 65,000 years ago, the Oruanui eruption about 26,500 years ago, which is responsible for the shape of the modern caldera, and the Hatepe eruption, dated 232 ± 10 CE. Taupō began erupting about 300,000 years ago.
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