Physical factors that impact the faulting and stability of ocean island volcano flanks

Ocean island volcanoes expand laterally when their flanks slip outward along faults or, on rare occasions, when they catastrophically collapse. The south flank of Kīlauea, a volcano on the Big Island of Hawai‘i, for example, slips seaward along both its basal décollement as well as along the Hilina normal fault, a potentially shallower structure interpreted from seismic profiles. Our goal was to explore the physical conditions that promote flank stability versus basal slipping or shallow faulting. With 2-D finite-difference models, we characterized fault behavior in response to variations in physical parameters, including volcanic slope, presence and location of a shoreline, frictional strength, pore-fluid pressure, and magmatic intrusions. Models successfully produced stable and unstable flanks consistent with the angle of repose for either subaerial or submarine flanks. Models also indicated that the presence of a shoreline—a dual subaerial-submarine case—as well as high pore-fluid pressure tended to destabilize the flank. Models run with magma chambers did not show that the stability of the flank depends on the presence of low viscosity bodies, but there were many variables introduced in this category and not all of them were tested for their contributions to the flank’s stability.