CHARACTERIZATION OF FLANK ERUPTIONS USING PALEO-STRESS FIELDS: AKAROA, NEW ZEALAND

Flank eruptions pose a considerable hazard to communities living on active volcanic systems and significantly increase the area volcanologists must monitor for signs of unrest. Evaluating volcanic activity for signs of potential flank eruption poses considerable challenges. However, investigating the stress evolution of a growing volcanic system can reduce the spatial uncertainty of eruption forecasts and help us assess the potential for flank eruption. In this study, we combine field, petrographic, and seismic tomography data from New Zealand’s Akaroa volcano with finite element models to investigate the system’s paleo-stress field during the emplacement of a suite of radiating dikes and flank eruptions. Field mapping indicates that dikes exposed along Akaroa’s erosional crater rim have predominantly radial orientations and are found within a narrow elevation range. As no obvious material or structural control is evident to explain the observed elevation range, we postulate the depth of dike emplacement was dictated by the presence of a stress barrier along which ascending, radially aligned dikes deflected before emplacement on the flanks of Akaroa. Numerical simulations of the Akaroa system designed to test this hypothesis suggest the dikes were emplaced after the Akaroa volcano reached its maximum edifice height. Stresses generated by viscoelastic relaxation and lithospheric flexure are not favorable for the propagation and emplacement of radial dikes. This study provides a new technique for investigating the stress evolution of a volcanic system, and potentially forecasting eruptions at active analogs to the Akaroa system, such as Hawaii’s Kilauea volcano.