Role of tectonic stress and topography on repeated lateral dikes: application to the 1975-1984 Krafla and 2023-2025 Svartsengi rifting episodes in Iceland.

Lateral dike intrusions into rift zones, repeated in temporal sequences, depend on intrinsic and extrinsic factors including pressure build-up where magma accumulates between intrusions, and the local stress regime influenced by tectonic stress and topography. We reexamine these effects by revising a simplified elastic model of rifting by Buck et al. (2006), where topographic gradients and tectonic stress, in addition to magma accumulation, contribute to the driving pressure of dike propagation. Our model (i) introduces a three-section dike geometry, (ii) assumes lateral dike intrusions follow a positive pressure gradient and open in the part of the rift zone where the local maximum of driving pressure occurs, (iii) restricts the amount of dike opening according to tectonic stress stored prior to a rifting episode, and (iv) incorporates magma compressibility to better understand volume change in a magma domain. As successive intrusions redistribute stress, dike opening is favored at different parts along the rift zone. When applied to the 1975-1984 Krafla rifting episode, the model predicts a spatial distribution of dike openings consistent with geophysical observations, with magma flow into the Krafla fissure swarm through an inlet located ~ 2-4 km north of the Krafla caldera center. Inferred magma pressure at the inlet at the initiation of the first dike is ~ 1-10 MPa above lithostatic stress, whereas tectonic stress and topographic effects contributed > 20 MPa to the driving pressure. The failure pressure limit for the first dike is found to be larger than that for later dikes by a factor of 2. The lower failure limit for later dikes and tectonic stress allow magma flow into subsequent dikes when magma pressure at the inlet is below lithostatic. The model is also applied to fit the spatial distribution of dike openings in the beginning of the 2023-2025 Svartsengi rifting episode in SW Iceland. There, topographic effects contribute ~ 2 MPa of driving pressure to the southern propagation of the first dike. Tectonic stress and significant magma buoyancy (up to 9 MPa) enable dike initiations when the overpressure from magma recharge in the domain was below lithostatic. Tectonic stress inhibited eruption from the initial dike of the Svartsengi rifting episode. Our findings demonstrate that tectonic stress and topographic effects are critical factors driving lateral dike propagation, allowing magma flow into dikes or eruptions under low magma pressure, even lower than lithostatic pressure. Supplementary information: The online version contains supplementary material available at 10.1007/s00445-025-01897-y.