360 Intrusions in a Miniature Volcano: Birth, Growth, and Evolution of an Analog Edifice

Allan Derrien,Benoit Taisne

doi:10.3389/feart.2019.00019

Abstract

Volcanoes throughout the world have been monitored with complete geophysical data for no more than three decades, a relatively short time compared to their overall life. The consequence is that we lack a long observation of volcanic growth and behavior to get a more complete picture of the interaction between edifice stress state and magma transfer. Here we present the birth and evolution of a 83x83 cm analog model, where we reproduce for the first time volcanic growth over 360 successive intrusions (15 mL every half hour, at a rate of 3 mL/min) in an analog elasticity-dominated material (pigskin gelatine). Our model volcano started as a flat topography and ended 3.82 cm in height at the summit. It displayed cyclic eruptive patterns with alternating phases of eruptive and purely intrusive behavior. Alike to many intraplate volcanoes in nature, main dyke swarms produced in the experiment were disposed in a three-branched star pattern centered above the injection source (“volcanic rift zones”). Two radial sill networks, at source depth and edifice base, surrounded them. The interaction of edifice growth and magma transfer was dominated by long-term radial compressive stress building during dyke swarming and radial compressive stress release/compensation during sill emplacement. Near-surface stresses, deduced from the main orientation eruptive fissures and “dry” fractures, became more localised as the volcano grew. At the end of the experiment, the shallow stress field was interpreted as generally extensional radial at the summit, extensional tangential on the flanks, and compressive radial in distal areas.

Highlights

Shield oceanic island volcanoes, such as Kilauea, Piton de la Fournaise or Pico de Fogo, often form far from active tectonics boundaries
If the regional stress field is weak, dyke propagation is likely to be influenced by volcano-related stress fields, as reservoir overpressure, cumulative edifice deformation under repeated intrusions, edifice gravitational loading (Hyndman and Alt, 1987; Kervyn et al, 2009; Roman and Jaupart, 2014) or unloading (e.g., Corbi et al, 2015; Maccaferri et al, 2017)
We found scaling surprisingly close in this case, suggesting that experiments such as the one presented in this communication might be of worth for real-world volcanoes studies. This model was limited by the use of gelatine as a crustal analog: it proved hard, even with precautions learnt from earlier experiences, to maintain its stability and mechanical properties after 400 injections (8 days), and achieve longer observation periods

Summary

Introduction

Shield oceanic island volcanoes, such as Kilauea, Piton de la Fournaise or Pico de Fogo, often form far from active tectonics boundaries. The source of magma for this final transfer can vary greatly It can display a well-developed reservoir with a complex geometry as Kilauea (e.g., Ryan, 1988; Zhai and Shirzaei, 2016), include a single main chamber as Piton de la Fournaise (e.g., Michon et al, 2015, 2016), or have no identified voluminous shallow reservoir as Pico de Fogo (e.g., Mata et al, 2017) (Figure 1). In this ultimate phase of the volcanic fluids journey to the surface, magma usually propagates through the intrusion of dykes or sills into the host rock, if no open conduit is available

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Conclusion