Understanding the evolution of magma systems between two super-eruptions to support inter-agency planning and unrest response

The two youngest supereruptions in the central Taupō Volcanic Zone (TVZ), Whakamaru (349 ka) and Ōruanui (25.4 ka), have been extensively studied but the tempo and nature of volcanism in the Taupō-Maroa area between these two events is less documented. Eruptives spanning this period have been studied using petrology and dating in collaboration with emergency managers, mana whenua (sub-tribe that has authority) and GeoNet volcano monitoring through the Caldera Advisory Group. There were six magma systems in existence from 349-25.4 ka, which in turn had deeper crustal roots reflecting two crustal greywacke terranes. Lavas of the Western Dome Belt age-bracket the Whakamaru event and reflect a long-lived magmatic system that was seemingly independent of the much larger Whakamaru system.

To support risk management and the interpretation of modern unrest through CAG, we have found that lava dome distributions in the area are influenced by tectonic structures and dome eruptions occur more frequently than previously thought, suggesting the most probable eruptive mode of rhyolitic caldera volcanoes is smaller dome-building eruptions. Temporal and spatial patterns of large explosive versus dome-building eruptions in the central TVZ during the 349-25.4 ka period strongly imply that the extreme thermal fluxes needed to drive magmatic systems for the large explosive eruptions varied greatly in intensity and moved around over a ~80 x 40 km area. This knowledge assisted with calibration of probabilities of the range in future scenarios during the recent 2022-23 unrest at Taupō, that led to the first ever supervolcano volcanic alert level rise.