Evolution of magma conduits during the 1998–2000 eruptions of Piton de la Fournaise volcano, Réunion Island

Abstract

[1] At basaltic volcanoes, magma is transported to the surface through dikes (magmafilled fractures), but the evolution of these dikes as eruptions proceed is rarely documented. In March 1998, after five and a half years of quiescence, Piton de la Fournaise volcano (Réunion Island) entered into a new eruptive phase characterized by intense eruptive activity. Coeruptive displacements recorded by interferometric synthetic aperture radar (InSAR) for the first five eruptions of the cycle are analyzed using 3-D boundary element models combined with a Monte Carlo inversion method. We show that the eruptions are associated with the emplacement of lateral dikes rooted at depths of less than about 1000 m, except for the first March 1998 event where an additional deeper source is required. The dikes are located above preeruptive seismic swarms. This is consistent with nearly isotropic stress caused by repeated dike intrusions and low confining pressure enhanced by the presence of pores in the shallowest 1000 m of the edifice. The volumes of the modeled dikes represent 17% of the volume of emitted lava, showing that exogenous growth plays a major role in building the volcano. By taking into account the preeruptive seismicity and tilt data together with the results of InSAR data modeling, we find that dikes first propagate vertically from a source region below sea level before being injected laterally at shallow depth. This behavior is consistent with the presence of levels of neutral buoyancy at shallow depth in the edifice.

Magma sources involved in the 2002 Nyiragongo eruption, as inferred from an InSAR analysis

“…Indeed, the data fit breaks down when the southernmost part of the shallow dike is shortened by 5 km and replaced with a 5 km-long dike connecting the eruptive fissure to the deep dike. A similarly narrow path is also postulated for other volcanoes such as Piton de la Fournaise [Fukushima et al, 2010;Traversa et al, 2010].…”

“…[27] Here, following Fukushima et al [2005Fukushima et al [ , 2010 for dikes and Sun et al [2011] for faults, we determine the sources of the observed InSAR displacements by simultaneously inverting for a quadrangular fracture geometry, location and uniform stress changes on the dikes or faults, leading to non-uniform displacement distributions. The method used here [Fukushima et al, 2005] combines 3D numerical models, based on a boundary element numerical method [Cayol and Cornet, 1997], with nonlinear inversions, based on a near neighborhood algorithm [Sambridge, 1999a[Sambridge, , 1999b.…”

The interplay between collapse structures, hydrothermal systems, and magma intrusions: the case of the central area of Piton de la Fournaise volcano

“…At shallower depth, they can migrate laterally, probably because they encounter a level of neutral buoyancy Fukushima et al 2010). The column therefore also acts as a guide for the intrusions.…”

“…Modeling of ground displacements caused by dikes feeding the eruptions (e.g., Peltier et al 2005 and references therein; e.g., Fukushima et al 2010) shows that all the intrusions start at depth and rise vertically in the fractured column. At shallower depth, they can migrate laterally, probably because they encounter a level of neutral buoyancy Fukushima et al 2010).…”

Laboratory Modelling of Volcano Plumbing Systems: A Review

“…They are able to detect even subtle ground movements induced by changes in magma pressure or distribution at depth. Data from these methods are widely used to (i) forecast that an eruption is imminent (Sigmundsson et al 2010) and (ii) infer the geometry of volcanic plumbing system components, such as dykes (Wright et al 2006Fukushima et al 2010, cone sheets (Chadwick et al 2011), sills (Amelung et al 2000;Sigmundsson et al 2010) and magma reservoirs (Chang et al 2007).…”