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The Auckland volcanic field is an area of monogenetic volcanoes underlying much of the metropolitan area of Auckland, New Zealand's largest city, located in the North Island. The field's 53 volcanoes〔 (or thereabouts) have produced a diverse array of maars (explosion craters), tuff rings, scoria cones, and lava flows. Each volcano has erupted for just one period, lasting for weeks to several years, except for Rangitoto Island, which erupted repeatedly. The field is fuelled entirely by basaltic magma, unlike the explosive subduction-driven volcanism in the central North Island, such as at Mount Ruapehu and Lake Taupo.〔Ian E.M. Smith and Sharon R. Allen. ''(Auckland volcanic field geology )''. Volcanic Hazards Working Group, Civil Defence Scientific Advisory Committee. Retrieved 30 March 2013. Also published in print as ''Volcanic hazards at the Auckland volcanic field''. 1993.〕 Currently dormant, the field is likely to erupt again within the next "hundreds to thousands of years" (based on past events), a very short timeframe in geologic terms.〔Beca Carter Hollings & Ferner (2002). ''(Contingency Plan for the Auckland Volcanic Field )'', Auckland Regional Council Technical Publication 165. Accessed 2008-05-12.〕 ==Features== The field ranges from Lake Pupuke and Rangitoto Island in the north to Matukutururu (Wiri Mountain) in the south, and from Mount Albert in the west to Pigeon Mountain in the east. The first vent erupted at Onepoto Volcano 248,000 ± 28,000 years ago.〔M.O. McWilliams research, 2002, associated with Shane P, Sandiford A (2003) ''Paleovegetation of marine isotope stages 4 and 3 in northern New Zealand and the age of the widespread Rotoehu Tephra.'' (Quaternary Research ) 59:420-429〕 The most recent eruption (about 600 years ago〔 and within historical memory of the local Māori iwi) was of Rangitoto, an island shield volcano just east of the city, erupting 2.3 cubic kilometres of lava. The eruptions have tended to become bigger over time, with Rangitoto making up almost 60% of the field's entire volume of erupted material. All of the volcanoes are relatively small, most being less than 150 meters in height. Lake Pupuke, on the North Shore near Takapuna, is a volcanic explosion crater. A few similar craters such as Orakei Basin are open to the sea. The field has produced voluminous lava flows that cover much of the Auckland isthmus. One of the longest runs from Mt Saint John northward, almost crossing the Waitemata Harbour to form Meola Reef.〔Hayward, Murdoch, Maitland (2011). pp. 134–135.〕 More than 50 lava tubes and other lava caves have been discovered, including the 290 metre long Wiri Lava Cave.〔David Lomas (Winter 2006). "(Cave new world )". ''Heritage New Zealand''. New Zealand Historic Places Trust. Accessed 2007-05-04.〕 The second longest individual cave in the Auckland field, some in total length, is the Cave of a Thousand Press-ups to the east of One Tree Hill. Two impressive depressions caused by lava cave collapses are the Puka Street Grotto and the nearby Hochstetter Pond, also known as Grotto Street Pond, in Onehunga.〔Hayward, Murdoch, Maitland (2011). pp. 17–18.〕〔(【引用サイトリンク】title=Geology )〕 For most of the 250,000 years that the field has been erupting, the planet has been in glacial periods (ice ages) where sea levels were much lower due to water being locked up as ice, and the Waitemata and Manukau Harbours were dry land. All the volcanoes probably erupted on land except for Rangitoto, which erupted during the current interglacial (warmer) period.〔Hayward, Murdoch, Maitland (2011). pp. 2–3.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Auckland volcanic field」の詳細全文を読む スポンサード リンク
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