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

Thursday, 18 December 2014
Nicolas Villeneuve1, Valerie Ferrazzini1, Andrea Di Muro1, Aline Peltier1, Francois Beauducel2, Genevieve C Roult2, Thomas Lecocq3, Florent Brenguier4, Ivan Vlastelic5, Lucia Gurioli5, Stephane Guyard6, Thibault Catry7, Jean Luc Froger5, Diego Coppola8, Andrew John Lang Harris5, Massimiliano Favalli9, Alessandro Aiuppa10, Marco Liuzzo11, Gaetano Giudice11, 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)Institut de Physique du Globe de Paris, Paris, France, (3)Royal Observatory of Belgium, Brussels, Belgium, (4)University Joseph Fourier Grenoble, Grenboble, France, (5)Laboratoire Magmas et Volcans, Université Blaise Pascal, CNRS UMR 6524, IRD R 163, Clermont-Ferrand Cedex, France, (6)Conseil Régional de La Réunion, DADT-SIG/SEAS-OI, Saint Pierre, Reunion, (7)IRD, SEAS-OI, Saint Pierre, Reunion, (8)Università di Torino, Dipartimento di Scienze della Terra, Turin, Italy, (9)Istituto Nazionale di Geofisica e Vulcanologia, Pisa, Italy, (10)Università di Palermo, CFTA, Palermo, Italy, (11)Istituto Nazionale di Geofisica e Vulcanologia, Palermo, Italy
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.