A future magma inflation event under the rhyolitic Taupo volcano, New Zealand: Numerical models based on constraints from geochemical, geological, and geophysical data

Catastrophic, caldera-forming silicic eruptions and intervening smaller intra-caldera events represent a major volcanic hazard in many parts of the world. Central to monitoring and forecasting future eruptive activity at caldera volcanoes are (1) an accurate assessment of the present state of the volcanic system, and (2) a detailed understanding of the inter-relationships between the volcanic system and regional tectonics and crustal structure. Using Taupo volcano in the central North Island of New Zealand as a case example, we combine geochemical and geological information from the past behaviour of magma bodies with knowledge of the present geophysical state of the crust, in order to model a hypothetical inflation event in the subsurface magmatic system. Numerical models of the crust incorporating inelastic rheology, an extensional regional stress field, weak caldera fill, and embedded weak caldera-bounding faults show that these factors can substantially influence and localise the processes and signals accompanying the hypothetical pre-eruptive ascent and accumulation of magma. For Taupo volcano, the models demonstrate that surface displacements associated with inflation of magma bodies up to the order of 10  km3 in volume may be almost entirely hidden beneath Lake Taupo. These results highlight the difficulties in prediction of inflation events beneath calderas. There is a feedback between inflation and extensional tectonics, so that surface uplift on short timescales can be followed by subsidence on longer timescales. The model predictions provide a quantitative, targeted framework for monitoring Taupo volcano and for identifying any anomalous behaviour that may represent the onset of a future eruption. The results may also prove useful for interpretation of surface deformation on other caldera locations around the world.