Lowe, D.J., Shane, P.A.R., de Lange, P.J., Clarkson, B.D. 2016. Guidebook for Rangitoto Island AQUA field trip, Auckland, 2016. School of Science, University of Waikato, in association with the Australasian Quaternary Association (AQUA) Biennial Conference, Auckland, New Zealand, 5-9 December, 2016. 35 pp.
Permanent Research Commons link: http://hdl.handle.net/10289/10828
Rangitoto is arguably Auckland’s most beautiful and omnipresent landscape feature. It is a symmetrical, ~6-km wide, basaltic shield volcano that last erupted ~550‒500 cal. yr BP (c. 1400‒1450 AD), not long after the arrival and settlement of Polynesians in the Auckland region (c. 1280 AD). It is by far the largest, and the youngest, volcano in the Auckland Volcanic Field (AVF). The AVF consists of approximately 53 individual eruptive centres, all of which are within the boundaries of the Auckland urban area. Recent research on cryptotephras (defined below) in sediments from Lake Pupuke on North Shore and in wetlands on Motutapu Island, and on a 150-m-long drill core obtained in February, 2014, has revealed that Rangitoto has a much more complex history that previously thought, and may be better viewed as a ‘volcanic complex with multiple episodes of eruptions’ (Linnell et al. 2016). In summary, (1) activity commenced c. 6000 cal. yr BP involving minor effusive and pyroclastic volcanism; (2) a voluminous shield-building phase took place from c. 650550 cal. yr BP (c. 13001400 AD), forming the main island ediface; and (3) the final phase of activity, from c. 550500 cal. yr BP (c. 14001450 AD), was explosive and less voluminous, producing scoria cones at the summit. The flora on Rangitoto is unique among the islands situated in the Hauraki Gulf because of the island’s young age, and the fact that technically Rangitoto is an ‘oceanic’ island. Its flora and fauna are derived entirely from long distance dispersal. The island contains some 582 vascular plant taxa of which 228 (39%) are indigenous. Various other special ecological features, and studies on plant succession and their drivers, make the island a truly fascinating place to visit. At this time of year, we should see many pohutukawa (Metrosideros excelsa) trees in flower.
School of Science, University of Waikato
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