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Rangitoto Island is a volcanic island in the Hauraki Gulf near Auckland, New Zealand. The 5.5 km wide island is an iconic and widely visible landmark of Auckland with its distinctive symmetrical shield volcano cone rising 260 metres (850 ft) high over the Hauraki Gulf. Rangitoto is the most recent and the largest (2311 hectares)〔 of the approximately 50 volcanoes of the Auckland volcanic field.〔 It is separated from the mainland of Auckland's North Shore by the Rangitoto Channel. Since World War II it has been linked by a causeway to the much older, non-volcanic Motutapu Island. ''Rangitoto'' is Māori for 'Bloody Sky',〔(What happened to local Maori? ) (from the Rangitoto page on the GNS Science website)〕 with the name coming from the full phrase ''Ngā Rangi-i-totongia-a Tama-te-kapua'' ('The days of the bleeding of Tama-te-kapua'). Tama-te-kapua was the captain of the Arawa ''waka'' (canoe) and was badly wounded on the island, at a (lost) battle with the Tainui ''iwi'' (tribe) at Islington Bay.〔〔 ==Geology== Rangitoto was formed by a series of eruptions commencing at least 6000 years ago, with the most recent eruptions occurring between 550 and 600 years ago. The most recent eruptions occurred in two episodes, 10–50 yrs apart, and are thought to have lasted for several years during the later shield-forming episode. The first recent episode erupted most of the volcanic ash that mantles Motutapu Island next door, and produced the lower, northern, scoria cone. The second episode built most of Rangitoto erupting all the lava flows and main scoria cone at the apex.〔''Volcanoes of Auckland: The Essential Guide''. Hayward, B.W., Murdoch, G., Maitland, G.; Auckland University Press, 2011.〕 The 2.3 cubic kilometres of material that erupted from the volcano was about equal to the combined by all the previous eruptions in the Auckland volcanic field, which were spread over more than 250,000 years.〔(Rangitoto ) (from the Auckland Regional Council website)〕〔(Rangitoto ) (abridged article from ''New Zealand National Geographic'')〕 In 2013, scientists said new studies showed Rangitoto had been much more active in the past than previously thought, suggesting it had been active on and off for around 1000 years before the final eruptions around 550 years ago. In February 2014 a 150m deep hole was drilled through the western flank of Rangitoto. This revealed a history of activity going back at least 6000 years, with the bulk of activity post dating 3800 years. Civil Defence officials said the discovery didn't make living in Auckland any more dangerous, but did change their view of how an evacuation might proceed. The hypothesis that Rangitoto may have erupted off and on for a long period before the main eruptions would be highly unusual for a monogenetic volcano and the evidence for this scenario has been disputed by some geologists〔Hayward, B.W., Grenfell, H.R., 2013. Did Rangitoto erupt many times? Geoscience Society of New Zealand Newsletter 11, 5-8.〕 The volcano is not expected to become active again, although future eruptions are likely within the volcanic field. Subsidence back down the throat during the cooling process has left a moat-like ring around the crater summit, which may be viewed from a path which goes right round the rim and up to the highest point.〔(Hauraki Gulf Islands – Rangitoto Island ), Auckland City Council. Updated September 2008. Retrieved 29 April 2009.〕〔 In some parts of the island, fields of lightweight, clinker-like black lava stones called scoria are still exposed, appearing very recent to a casual eye. About 200 metres from the top of the mountain on the eastern side visitors can walk through some of about seven known lava tubes — tubes left behind after the passage of liquid lava. The more accessible of the caves are signposted.〔 Lava tubes are formed when low-viscosity molten lava known as pahoehoe flows and cools on the outside due to contact with the ground and air, to form a hard crust allowing the still-liquid molten lava to continue to flow through inside. At Rangitoto the large tubes are cave-like. A torch is needed to explore the caves. The longest known cave is about 50 m long.〔Auckland University, Geology Dept, field guide〕 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「Rangitoto Island」の詳細全文を読む スポンサード リンク
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