Integrating LiDAR to unravel the volcanic architecture and eruptive history of the peralkaline Tūhua (Mayor Island) volcano, New Zealand

Abstract

Tūhua (Mayor Island), located off New Zealand's Bay of Plenty coastline, is a compound, shield-like volcano dominated by peralkaline rhyolite lavas and pyroclastic rocks. Previous studies have established the likely different timing and types of volcanism expressed by the volcano, but interpretation has been hindered by the rugged, shrub-covered terrain. Here we present a revised geological map, stratigraphic framework and geological history based on existing work, a 1 m digital elevation model, 100 m bathymetry and new field observations.

We identify three caldera/crater structures; the 36,000 year old C1 caldera, 9,200 year old C2 caldera and a newly identified 7,600 year old C3 crater. Our analysis suggests that the Tūhua eruption (7,600 years ago) is not related to collapse or formation of the C2 caldera, as interpreted by previous studies, but the newly identified C3 crater and its associated ejecta ring.

Coastal exposures include thick cone building pyroclastics and deposits of pyroclastic density currents alternating with lava flows exhibit the dominance of hydrovolcanism for explosive activity. Consequently, explosive interaction between magma and water is the most probable scenario for the initial stage of future eruptions.