How Magmatic Storage Regions Attract and Repel Propagating Dikes

Abstract

We investigate the effect of magmatic reservoir pressure on the propagation of dikes that approach from below, using analogue experiments. We injected oil into gelatin and observed how dike propagation responded to the stress field around a pressurized, spherical reservoir, filled with water. The reservoir was modeled using two different setups: one simply using an inflatable rubber balloon and the other by constructing a liquid-filled cavity. We find that the dike's response is dependent on the sign of the reservoir pressure (i.e., inflated/overpressurized and deflated/underpressurized) as well as on the dike's initial orientation (i.e., if its strike is radially, circumferentially, or obliquely oriented to the reservoir). Dikes that are initially strike radial respond, respectively, by propagating toward or away from overpressurized or underpressurized reservoirs, taking advantage of the reservoir's hoop stresses. Otherwise-oriented dikes respond by changing orientation, twisting and curling into a form dictated by the principal stresses in the medium. For overpressurized reservoirs, they are coaxed to propagate radially to, and therefore approach, the reservoir. For underpressurized reservoirs, they generally reorient to propagate tangentially, which causes them to avoid the reservoir. The magnitude of reservoir pressure controls at which distance dikes can be affected, and, at natural scales, we estimate that this occurs within a radius of a few tens of kilometers. This diminishes with time, due to viscous stress relaxation of the crust, which will occur on a timescale of hundreds of years.Plain Language Summary Magma commonly moves up toward the surface by creating cracks in the crust. It flows inside of the cracks and propagates by applying pressure that drives the flow and damages surrounding rocks. Nature always finds the easiest path for the crack, so if it takes less pressure to push apart the ground vertically or horizontally, the crack will grow accordingly. As it makes its way to the surface, it may encounter local stress variations that change its propagating direction. This applies near magma storage regions, below volcanoes. If such a region is highly pressurized or deflated, then nearby cracks will "feel" the change in their surrounding conditions and react by aligning in a direction of favorable stress. This makes it look like they are growing toward or circling around the storage region, respectively. We studied this behavior using scaled model experiments in laboratory conditions. We use different types of materials to represent nature, such as gelatin as rock and oil as magma. We were able to show how these cracks change shape for different reservoir pressures. We found that after a large eruption, subsequent eruptions are more likely to occur farther from the summit of a volcano.

New Insight Into a Volcanic System: Analogue Investigation of Bubble‐Driven Deformation in an Elastic Conduit

“…Indeed, gelatin shows a variable behavior depending on its state (elastic to viscoelastic rheology in the solid one and viscous rheology in the nonsolid one), composition, concentration, temperature, ageing, and the applied strain rate (Barrangou et al, ; Bot et al, , ; Kavanagh et al, ; Kavanagh & Ross‐Murphy, ; Norziah et al, ). Gelatin is often used as rock analogue to study shallow crustal processes, especially propagation of dykes (Heimpel & Olson, ; Muller et al, ; Pansino et al, ; Pansino & Taisne, ; Rivalta et al, ; Takada, ) as it can scale to the Earth's crust. It has also been used to simulate the volcanic edifice (Acocella & Tibaldi, ; Walter & Troll, ).…”

“…The characteristics of this state of the gelatin are assumed to be representative of the elastic way the Earth's upper crust behaves in presence of instantaneously applied stress (Ranalli, ). Following Pansino and Taisne (), we measured the shear modulus before each experiment, which was consistent across experiments. An average value of 5000 Pa is used in this study.…”

The dynamics of large silicic systems from satellite remote sensing observations: the intriguing case of Domuyo volcano, Argentina

“…Such systems can have significant variations in the duration and intensity of deflation and inflation episodes, sometimes with eruptions, that are attributable to the steady growth of caldera resurgence 33 . Beyond conceptual models for surface manifestations of magma influx at depth, physics-based laboratory and numerical models suggest that magma emplacement history and the flux of magmatic episodes play roles in determining whether magma remains trapped in the upper crust or leads to dike propagation to the surface 44,45 . Scaled laboratory models 45 suggest that the threshold for propagating dikes that lead to eruption is around 1 m 3 /s, or about 0.03 km 3 /year.…”

“…Beyond conceptual models for surface manifestations of magma influx at depth, physics-based laboratory and numerical models suggest that magma emplacement history and the flux of magmatic episodes play roles in determining whether magma remains trapped in the upper crust or leads to dike propagation to the surface 44,45 . Scaled laboratory models 45 suggest that the threshold for propagating dikes that lead to eruption is around 1 m 3 /s, or about 0.03 km 3 /year. This is approximately the influx rate we infer for Domuyo (< 0.037 km 3 /year), and also similar to that of nearby Laguna del Maule 15,46 (~ 0.03-0.04 km 3 /year).…”

An experimental approach to dike propagation : the effects of stress, solidification and internal flow

“…We recorded the experiments using typical cameras, which took a time lapse of photographs from different perspectives and allowed us to track the dikes' position and geometry (see Pansino & Taisne, 2018, for data repository). We took photos in 18-MP resolution at a frequency of 6 photos per minute, which was high relative to the dike velocity (generally <1 mm of propagation between photos).…”