23-10 Emplacement Rates of Auckland Volcanic Field Lava Flows Using Groundmass Textures, Cooling Experiments, and Flow Models

Session: Subduction Zones and Their Volcanic Arcs: Initiation and Evolution, Structure, Metamorphism, Magmatism (Posters)

Poster Booth No.: 24

Presenting Author:

Brady Giles

Authors:

Giles, Brady Matthew¹, Teasdale, Rachel², Harp, Andrew³, Rowe, Michael⁴

(1) Earth and Environmental Sciences, California State University, Chico, Chico, CA, USA, (2) Earth and Environmental Sciences, California State University, Chico, Chico, CA, USA, (3) Earth and Environmental Sciences, California State University, Chico, Chico, CA, USA, (4) Faculty of Science, University of Auckland, Auckland, New Zealand,

Abstract:

The Auckland Volcanic Field (AVF) is a basaltic intraplate volcanic system composed of 53 small basaltic cones that formed between ~193 ka and 500 ya [1]. Volcanic activity has accelerated over the past 60 ka, and the AVF may still be “in its infancy” [2], presenting potential hazards for the Auckland region. This study aims to characterize lava-flow emplacement and cooling rates at two volcanic centers within the AVF. Rangitoto is the youngest edifice in the field (504 ya; [3]), and is located 13 km offshore Auckland. Te Kōpuke/Mount St. John (75 ka; [2]), is located in the city limits and produced the longest lava flow in the AVF (11 km; [4]). Differences in groundmass plagioclase crystallinities in proximal and distal samples help to determine microphenocryst growth rates. Results indicate flow durations of 8.5 hours for Rangitoto and 141.9 hours for Te Kōpuke/Mount St. John. These values correspond to emplacement rates of 0.18 km/hr and 0.07 km/hr, respectively. The effusion rate and eruption duration for Rangitoto are 1 m³/s and 70 hours, respectively, based on relationships with flow lengths and cone heights [5]. Using emplacement parameters predicted by FLOWGO [6] and Q-LavHA, [7] emplacement models generate final lava flow extents and aspect ratios that closely match observed morphologies for Rangitoto. Further work will use 1-atm cooling experiments to reproduce natural groundmass crystallinities to refine AVF lava cooling rates and emplacement durations. Emplacement parameters in the AVF will be further constrained using multiple lines of evidence of lava flow measurements, predictive flow models (FLOWGO and Q-LavHA), and experimental results. These parameters may ultimately support civil defense and emergency management efforts by improving estimates of emplacement timelines during potential future eruptions.

[1] Hopkins et al., 2020; [2] Leonard et al., 2017; [3] Needham et al., 2011; [4] Rhodé, 2016; [5] Browne et al., 2010; [6] Harris and Rowland, 2000; [7] Mossoux, 2016

Geological Society of America Abstracts with Programs. Vol. 58, No. 3, 2026

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