MODELLING HEAT EXTRACTION FROM MAGMA BODIES AT DEPTH IN THE CENTRAL TVZ

Improving our understanding of how large (>50 km³), eruptible magma bodies interact with overlying hydrothermal systems and the crust is important for improving volcanic monitoring and geothermal energy systems. The Central Taupo Volcanic Zone is an ideal place for this research due to its history of caldera-forming eruptions and hydrothermal energy in the region. It has been shown that pumice-hosted quartz crystals present in the pyroclastic deposits of these caldera-forming eruptions crystallized on the order of decades prior to eruption; however, there is currently no understanding of a mechanism for heat extraction that could facilitate such rapid time scales. This study uses rhyolite-MELTS and multiple heat transfer equations for conductive and convective heat loss in order to establish if heat can be lost from a large cooling magma body over decades. Conductive heat transfer alone is found to transfer the heat required over millennia, and convective heat transfer with a power output of ≤775 MW transfers the required heat on the order of centuries. We conclude that no singular modern hydrothermal system with power output of <1000 MW can extract enough heat from a large, eruptible, silicic magma body on the order of decades; however, multiple hydrothermal systems of ~500 MW in close proximity may be candidates for this rapid heat transfer. Our findings suggest that hydrothermal systems may be a necessary mechanism for rapid decadal-scale quartz crystallization and eruption of shallow silicic magma bodies, and thus further research could provide new insight into the monitoring of restless calderas.