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Ngauruhoe in the Taupo Volcanic Zone, produced andesite flows in 19 and avalanche deposits in 1975.Potassium-argon “dating” of five of these flows and deposits yielded K-Ar model “ages” from Ar* content.Ruapehu (about 12 km to the south), Ngauruhoe is an imposing, almost perfect cone that rises more than 1000 m above the surrounding landscape.Eruptions from a central 400 m diameter crater have constructed the steep (33°) outer slopes of the cone.34 The Taupo Volcanic Zone, a volcanic arc and marginal basin of the Taupo-Hikurangi arc-trench (subduction) system,5 is a southward extension on the Tonga-Kermadec arc into the continental crustal environment of New Zealand’s North Island.
Nearly all vents active within the last 10 ka lie on a gentle arc which extends 25 km north-northeast from the Rangataua vent on the southern slopes of Ruapehu through Ruapehu summit and north flank vents, Tama Lakes, Ngauruhoe, Red Crater, Blue Lake, and Te Mari craters.
The Ngauruhoe area was accessed from State Highway 47 via Mangateopopo Road. Care was taken to ensure correct identification of each lava flow and that the samples collected were representative of each flow and any variations in textures and phenocrysts in the lavas.
From the parking area at the end of the road, the Mangateopopo Valley walking trail was followed to the base of the Ngauruhoe cone, from where the darker-colored recent lava flows were clearly visible and each one easily identified on the northwestern slopes against the lighter-colored older portions of the cone (fig. Eleven 2–3 kg samples were collected: two each from the February 11, 1949, June 4, 1954, and July 14, 1954, lava flows and from the February 19, 1975, avalanche deposits; and three from the June 30, 1954 lava flows. All samples were sent first for sectioning one thin section from each sample for petrographic analysis.
It has been interpreted as oblique subduction of the Pacific plate beneath the Australian plate.
The zone extends approximately 300 km north-northeast across the North Island from Ohakune to White Island (fig.Intermittent explosive eruptions and spectacular lava fountaining during June and July 1954 built a spatter-and-cinder cone around the south sub-crater, modifying the western summit of the mountain.