Abstract
Dikes feed most eruptions, so understanding their mechanism of propagation is fundamental for volcanic hazard assessment. The variation in geometry of a propagating dike as a function of the injection rate remains poorly studied. Here we use experiments injecting water into gelatin to investigate the variation of the thickness, width and length of a flux-driven dike connected to its source as a function of the injection time and intruded volume. Results show that the thickness of vertically propagating dikes is proportional to the injection rate and remains constant as long as the latter is constant. Neither buoyancy nor injected volume influence the thickness. The along-strike width of the dike is, however, proportional to the injected volume. These results, consistent with the inferred behavior of several dikes observed during emplacement, open new opportunities to better understand how dikes propagate and also to forecast how emplacing dikes may propagate once their geometric features are detected in real-time through monitoring data.
Highlights
The dominant mechanism of magma transfer in the upper crust is via magma-filled cracks, including steeply dipping dikes
We have investigated the variation of the geometric parameters of a continuously fed flux-driven dike as a function of the injection rate
As we wanted to test the role of the injection rate on the geometry of the propagating dike, we did not change any other possible parameter affecting the dike geometry, such as the viscosity of magma and the mechanical properties of the host rock, which may vary in nature (Lister and Kerr, 1991; Rivalta et al, 2005; Rivalta and Dahm, 2006; Rivalta et al, 2015)
Summary
The dominant mechanism of magma transfer in the upper crust is via magma-filled cracks, including steeply dipping dikes. There are several external factors potentially controlling dike propagation, such as tectonic stresses or topographic loads, the main pressures acting on a propagating dike fed by its source are the excess or elastic pressure Pe, the source pressure ΔPr, the buoyancy pressure Pb, the viscous pressure drop Pv, and the fracture pressure Pf (Pollard, 1987; Lister and Kerr, 1991; Rubin, 1995; Menand and Tait, 2002; Canon-Tapia and Merle, 2006; Taisne et al, 2011; Kavanagh et al, 2013; Rivalta et al, 2015). Laboratory experiments modeling a flux-driven dike fed from its source show an increase in width with time and with volume (Kavanagh et al, 2018); the possibility that different injection rates determine different dike widths remains unclear
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