Fig. 4

Dyke propagation paths. a–c Dyke trajectories with increasing effective volcanic loading (EVL), and constant unloading (quadratic decay), d–f dyke trajectories with constant EVL magnitude, constant unloading (quadratic decay), but with varying EVL types (d-triangular, e-trapezoidal and f-planar), g–i dyke trajectories with EVL₂ = 0.4 but with different unloading (linear, quadratic and cubic decay, from g to i, respectively), l–n same as g–i, respectively, but with reduced buoyancy of the dyke intrusions. In all panels, the colour contour is the horizontal stress change due to the topography (superposition of loading and unloading stresses). The grey dashed lines indicate the directions of maximum compression. The dyke initial cross sections are shown in red. Dyke paths are the black solid curves. The dashed line at z = 0 represents the sea level, and the solid line at z = −2 km is the base of the volcanic edifice (upper boundary of the numerical model). The grey area represents the unloading force distribution used to simulate the flank collapse. A simplified cross section of the W-E topography profile of Fogo Island is shown in each panel. x = 0 is the position of the Pico do Fogo stratocone. x _e is the arrival position of the upper tip of the closest dyke to Pico do Fogo. x* marks the position at the base of the crust (z = −15 km), where dykes separate between those that will propagate towards the western flank and those that will propagate towards the eastern flank of the volcano. The initial dyke distribution is centred at x = −4 km, i.e., the centre of the pre-collapse volcanic cone