The June 2014 eruption at Piton de la Fournaise: Robust methods developed for monitoring challenging eruptive processes

Nicolas Villeneuve1, Valerie Ferrazzini1, Andrea Di Muro2, Aline Peltier1, Francois Beauducel3, Genevieve C Roult4, Thomas Lecocq5, Florent Brenguier6, Ivan Vlastelic7, Lucia Gurioli7, Stephane Guyard8, Thibault Catry9, Jean-Luc Froger10, Diego Coppola11, Andrew John Lang Harris7, Massimiliano Favalli12, Alessandro Aiupa13, Marco Liuzzo14, Gaetano Giudice15, Patrice Boissier1, Christophe Brunet1, Philippe Catherine1, Fabrice J Fontaine1, Laura Henriette1, Frederic Lauret1, Audrey Riviere1 and Philippe Kowalski1, (1)IPGP, Observatoire Volcanologique du Piton de la Fournaise, Bourg Murat, France, (2)Université de Paris, Institut de Physique du Globe de Paris, Paris, France, (3)Université de Paris, Institut de Physique du Globe de Paris (IPGP), UMR 7154, Paris, France, (4)Institut de Physique du Globe de Paris, Paris, France, (5)Royal Observatory of Belgium, Brussels, Belgium, (6)University Grenoble Alpes, ISTerre, Grenoble, France, (7)Laboratoire Magmas et Volcans, Université Blaise Pascal, CNRS UMR 6524, IRD R 163, Clermont-Ferrand Cedex, France, (8)Conseil Régional de La Réunion, DADT-SIG/SEAS-OI, Saint Pierre, Reunion, (9)IRD, SEAS-OI, Saint Pierre, Reunion, (10)Saint Etienne Université, Saint Etienne, France, (11)University of Turin, Department of Earth Sciences, Turin, Italy, (12)Istituto Nazionale di Geofisica e Vulcanologia, Pisa, Italy, (13)Università di Palermo, CFTA, Palermo, Italy, (14)Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Palermo, Palermo, Italy, (15)Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo, Catania, Italy
Abstract:
After almost 3.5 years of quiescence, Piton de la Fournaise (PdF) produced a small summit eruption on 20 June 2014 at 21:35 (GMT). The eruption lasted 20 hours and was preceded by:

i) onset of deep eccentric seismicity (15-20 km bsl; 9 km NW of the volcano summit) in March and April 2014;

ii) enhanced CO2 soil flux along the NW rift zone;

iii) increase in the number and energy of shallow (<1.5 km asl) VT events.

The increase in VT events occurred on 9 June. Their signature, and shallow location, was not characteristic of an eruptive crisis. However, at 20:06 on 20/06 their character changed. This was 74 minutes before the onset of tremor. Deformations then began at 20:20.

Since 2007, PdF has emitted small magma volumes (<3 Mm3) in events preceded by weak and short precursory phases. To respond to this challenging activity style, new monitoring methods were deployed at OVPF. While the JERK and MSNoise methods were developed for processing of seismic data, borehole tiltmeters and permanent monitoring of summit gas emissions, plus CO2 soil flux, were used to track precursory activity. JERK, based on an analysis of the acceleration slope of a broad-band seismometer data, allowed advanced notice of the new eruption by 50 minutes. MSNoise, based on seismic velocity determination, showed a significant decrease 7 days before the eruption. These signals were coupled with change in summit fumarole composition.

Remote sensing allowed the following syn-eruptive observations:

- INSAR confirmed measurements made by the OVPF geodetic network, showing that deformation was localized around the eruptive fissures;

- A SPOT5 image acquired at 05:41 on 21/06 allowed definition of the flow field area (194 500 m2);

- A MODIS image acquired at 06:35 on 21/06 gave a lava discharge rate of 6.9±2.8 m3 s-1, giving an erupted volume of 0.3 and 0.4 Mm3.

- This rate was used with the DOWNFLOW and FLOWGO models, calibrated with the textural data from Piton’s 2010 lava, to run lava flow projections; showing that the event was volume limited.

Preliminary sample analyses suggest that the olivine rich lavas have a differentiated character (melt MgO: 5.8 - 6.2 wt.%); proof of chamber residence. However, some aphyric tephra are more primitive (MgO: 8.2 wt.%). This suggests eruption due to injection of a small volume of new magma that destabilized an old magma pocket.

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