Interplay of Tectonics and Topography Facilitated Sudden Dyke Intrusion in 2022 at São Jorge Island, Azores

Oblique slow rifting in a hotspot setting has created a distributed volcanic zone in the central part of the Azores but it's unclear what causes focusing of magma upflow under the islands within a wide plate boundary deformation zone. For São Jorge Island, we use a three-dimensional finite element model to evaluate crustal stress from the interplay between topography and stretching of an elastic-viscoelastic lithosphere. This interplay generates high extensional stress beneath the island, favorable for dike injections. In 2022, geodetic and seismic observations reveal that magma ascended through a dyke to 2–3 km of the surface within hours, before propagating laterally and downward. Our model indicates that shallow ascent was mainly driven by topographic loading, while lateral migration was mainly promoted by tectonic spreading and a thickened viscoelastic crust.