EGU General Assembly 2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Dyke-sill propagation in glacial-volcanotectonic regimes: The case study of Stardalur laccolith, SW Iceland

Kyriaki Drymoni1, Alessandro Tibaldi1,2, Federico Pasquaré Mariotto3, and Fabio Luca Bonali1,2
Kyriaki Drymoni et al.
  • 1Department of Earth and Environmental Sciences, University of Milan-Bicocca, 20126 Milan, Italy
  • 2CRUST-Interuniversity Center for 3D Seismotectonics with Territorial Applications, 66100 Chieti Scalo, Italy
  • 3Department of Human and Innovation Sciences, Insubria University, Como, Italy

Dykes (Mode I extension fractures) supply magma from deep reservoirs to the surface and subject to their propagation paths, they can sometimes reach the surface and feed volcanic eruptions. Most of the times they mechanically stall in the heterogeneous crust or deflect through pre-existing fractures forming sills. Although several studies have explored dyking in heterogeneous regimes, the conditions under which dykes propagate in glacial-volcanotectonic regimes remain unclear.

Here, we coupled field observations with FEM numerical modelling using the software COMSOL Multiphysics (v5.6) to explore the mechanical and geometrical conditions that promote (or not), dyke-sill propagation in glacial-tectonic conditions. We used as a field example the Stardalur cone sheet-laccolith system, located in the Esja peninsula proximal to the western rift zone. The laccolith is composed of several vertical dykes that bend into sills and form a unique stacked sill ‘flower structure’. We modelled a heterogeneous crustal segment composed of lavas (top) and hyaloclastites (bottom). We then studied the emplacement of a dyke with varied overpressure values (Po = 1-10 MPa) and regional extension (Fe = 0.5-3 MPa) loading conditions at the lava/hyaloclastite contact. In the second stage, we added an ice cap as a body load to explore dyking subject to unloading due to glacier thickness variations (0-1 km).

Our results have shown that the presence of the ice cap can affect the dyke-sill propagation and the spatial accumulation of tensile and shear stresses below the cap. The observed field structure in non-glacial regimes has been formed either due to the mechanical contrast (Young’s modulus) of the studied contact, a compressional regime due to pre-existing dyking or faulting, or finally, high overpressure values (Po  ≥ 5 MPa). Instead, in a glacial regime, the local extensional stress field below the ice cap encourages the formation of the laccolith when the ice cap becomes thinner (lower vertical loads). Our models can be applied to universal volcanoes related to glacier thickness variation and sill emplacement.

How to cite: Drymoni, K., Tibaldi, A., Pasquaré Mariotto, F., and Bonali, F. L.: Dyke-sill propagation in glacial-volcanotectonic regimes: The case study of Stardalur laccolith, SW Iceland, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-6230,, 2023.