Eruptive histories of New Zealand’s nearshore volcanoes: Insights from marine cores around Tūhua & Whakaari volcanoes
Presentation
Authors: Jacqueline Grech Licari, Simon J. Barker, Colin J. N. Wilson, Pip F. Tildesley, Craig A. Miller, Jenny Stein
Event: IAVCEI 2024 Commission on Tephrochronology
Summary: Investigating the pyroclastic eruptive histories from marine piston cores collected in October 2023 at locations around Whakaari and Tūhua volcanoes.
Abstract:
New Zealand hosts two recently active near-shore volcanoes in the Bay of Plenty: Tūhua (Mayor Island) and Whakaari (White Island). Both volcanoes show evidence for explosive activity as well as caldera and/or flank collapses that may have impacted mainland New Zealand in the past. Whakaari’s eruptive history is only partially known due to limited exposure and preservation. Tūhua’s geology has been studied extensively but the full extent and ages of its recent explosive activity, especially that accompanying lava extrusion, remain uncertain. Understanding the magnitude and frequency of past eruptions is crucial for hazard and risk assessment for coastal communities.
Our study addresses these knowledge gaps by investigating the pyroclastic eruptive histories from marine piston cores collected in October 2023 at locations around both volcanoes. We will assess the numbers, ages, sizes, and compositions of eruptions, including radiocarbon dating of bracketing sediments (e.g., planktic foraminifera) and chemical analysis of tephra horizons (e.g., EPMA, LA-ICPMS) to calculate eruption frequency-magnitude relationships. Initial processing of the 37 recovered cores up to 5.5 m in length revealed >360 visible tephra layers in total. The number of discrete events will be determined once the layers are correlated.
Preliminary observations identify several large, but infrequent, peralkaline rhyolite eruptions from Tūhua, and multiple small, but more frequent, andesitic events from Whakaari. The cores also contain relatively young (<20ka) mainland calc-alkaline tephra from the Taupō Volcanic Zone, which facilitates good age constraints within the cores. Additionally, coarse-grained, poorly sorted, shell-rich tephra units observed in proximal Whakaari cores are evidence for mass flow activity. Preliminary observations from core processing alongside ongoing analyses (e.g., CT scanning, iTRAX, EPMA) will be presented and compared to onshore observations, existing tephra records and previous distal coring studies. These datasets will complement existing work to improve the eruptive record of New Zealand’s offshore volcanoes.