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Holocene eruptive histories of New Zealand's nearshore volcanoes: Insights from marine cores around Tūhua and Whakaari volcanoes

Jacqueline Grech Licari1 , Simon James Barker1, Colin James Ness Wilson1, Pip Frances Tildesley1, Craig Andrew Miller2

  • Affiliations: 1 School of Geography, Environment and Earth Sciences, Victoria University of Wellington, Wellington, New Zealand; 2 GNS Science, Wairakei Research Centre, Taupō, New Zealand.

  • Presentation type: Talk

  • Presentation time: Thursday 14:15 - 14:30, Room R280

  • Programme No: 2.2.5

  • Theme 2 > Session 2

Abstract

New Zealand (NZ) hosts two recently active near-shore island volcanoes in the Bay of Plenty: peralkaline rhyolite Tūhua (Mayor Island) and andesitic Whakaari (White Island). Both show evidence for explosive activity that may have impacted mainland NZ. Whakaari's eruptive history (<3 ka) is only partially understood, and it remains unknown whether the volcano produced large explosive eruptions. Tūhua's geology was studied extensively but the extent and ages of recent (<7.2 ka) explosive activity remain uncertain. Our study investigates the explosive eruptive histories of these volcanoes by examining marine piston cores from proximal and medial sites to refine the numbers, ages, sizes, componentry, and compositions of eruptions. Preliminary observations identify larger, infrequent eruptions from Tūhua, and smaller, but more frequent events from Whakaari. Mainland rhyolitic tephras from the mainland Taupō Volcanic Zone, including the 1314 AD Kaharoa, 232 AD Taupō and 8 ka Mamaku events, have been identified, providing good age constraints. Cores around Tūhua reveal at least two explosive peralkaline events younger than the ~7.2 ka caldera-forming eruption. A bimodal unit within several Whakaari cores confirms that the volcano erupted just before or simultaneously with the Kaharoa eruption. Coarse-grained, poorly sorted, shell-rich tephra units in proximal Whakaari cores indicate mass flow activity. Radiocarbon dating of bracketing sediments will determine whether these deposits represent one or multiple events, to assess tsunami generation potential. Results from ongoing analyses and initial age-depth models will be discussed and compared to onshore observations and existing tephra records to revise volcanic hazard assessments for mainland NZ.