Spatial and temporal variability in Hawaiian hotspot volcanism induced by small-scale convection

Volcanism far from plate boundaries is often attributed to an underlying mantle plume(1-6). However, enigmatic observations of Hawaiian volcanism, such as variations in the volume of erupted volcanic material through time(7,8), a geographical asymmetry in the geochemistry of the lavas(9-18) and secondary volcanism that occurs far away from the hotspot(15-20), cannot be explained by the classical mantle plume concept. Here we present a numerical model of mantle plume upwelling beneath Hawaii. We find that small-scale convection in the ambient mantle can erode the base of the lithosphere, creating a washboard topography on the underside of the plate. As the plate migrates over the upwelling plume, the plume interacts with alternating thicker and thinner sections of lithosphere to generate temporal variations in the flux of erupted volcanic material. The pre-existing washboard topography also causes the plume to spread and melt asymmetrically. In our simulations, this asymmetry in mantle flow generates an asymmetry in the chemistry of the erupted lavas. Finally, a more vigorous type of small-scale convection develops within the spreading plume, generating localized zones of upwelling well away from the hotspot. The associated magmatism is fed by chemically distinct material originating from the edges of the plume conduit. Our results show that shallow processes have an important influence on the character of volcanism fed by deep-rooted mantle plumes.