Rift zones of Piton de la Fournaise determined from the density maps computed from (a) 644 cinder cones (blue) and (b) 788 eruptive fissures (black lines). PRVA: Puy Ramond volcanic alignment. The dashed lines highlight cones organised concentrically around the western rim of the Enclos Fouqué caldera. Micron et al. (2015)

Understanding how and where magmas rises in the volcanic edifices of La Réunion is of importance for many topics, including volcanic hazard assessment and geothermal energy. The LGSR team has been devoted to this work for decades.

Our work shows that magma rises toward Piton de La Fournaise through complex, inclined pathways that are influenced by the fabric of the oceanic crust under La Réunion.

Magma ascent at Piton des Neiges has been also influenced by this crustal fabric.

 

Featured publication : Michon, L., Ferrazzini, V., Di Muro, A., Villeneuve, N., & Famin, V. (2015). Rift zones and magma plumbing system of Piton de la Fournaise volcano: How do they differ from Hawaii and Etna? Journal of Volcanology and Geothermal Research, 303, 112–129. doi.org/10.1016/j.jvolgeores.2015.07.031

 

 

 

Gravitational deformation (known as spreading) is concurrent to volcano growth during the lifetime of a volcanic edifice. Spreading may occur during eruption or in inter-eruptive periods, and may lead to rare bu catastrophic mass wasting events, such as for Mount St Helens in 1980.

Our team has devoted a large attention to the deformation of basaltic volcanoes in relationship with their eruptive or intrusive activity. Field work on an eroded volcano (Piton des Neiges) showed that sill intrusion is the most common mode of magma injection in an edifice. Sill intrusion may be explained by recurrent stress permutation in a volcanic edifice. Numerical simulation of sill intrusion suggests sills are able to generate lateral flank deformation. These simulations lead us to search for evidence of co-intrusive flank displacement during sill intrusion, which was found in 2016. Applying these results to Piton de la Fournaise, it is likely that the large flank sliding that occurred during the April 2007 eruption was due to a sill intrusion in the eastern flank of the edifice.

Featured publications :

Chaput, M., Famin, V., & Michon, L. (2014). Deformation of basaltic shield volcanoes under cointrusive stress permutations. Journal of Geophysical Research: Solid Earth, 119(1), 274–301.

Berthod, C., Famin, V., Bascou, J., Michon, L., Ildefonse, B., & Monié, P. (2016). Evidence of sheared sills related to flank destabilization in a basaltic volcano. Tectonophysics, 674, 195–209. http://doi.org/http://dx.doi.org/10.1016/j.tecto.2016.02.017

Cayol, V., Catry, T., Michon, L., Chaput, M., Famin, V., Bodart, O., … Romagnoli, C. (2014). Sheared sheet intrusions as mechanism for lateral flank displacement on basaltic volcanoes: Applications to Réunion Island volcanoes. Journal of Geophysical Research B: Solid Earth, 119(10), 7607–7635.

Froger, J. L., Famin, V., Cayol, V., Augier, A., Michon, L., & Lénat, J. F. (2015). Time-dependent displacements during and after the April 2007 eruption of Piton de la Fournaise, revealed by interferometric data. Journal of Volcanology and Geothermal Research, 296, 55–68.

Famin, V., & Michon, L. (2010). Volcano destabilization by magma injections in a detachment. Geology, 38(3), 219–222.

 

General view of the contact between mass wasting deposits (breccia) and a sill underneath. Note the sheared fabric of the two breccia layers, the contact sill and a sheared sill underneath. (Fig. 2 in Berthod et al., 206)

Displacement associated with the 2007 eruption, computed from two Envisat and three ALOS interferograms. The black box indicates the area for which ratios of displacements are computed. The coordinates are UTM WGS84 (zone 40S). Froger et al. (2015).

Sketches highlighting the differences in deformation and magmatic activity between Hawaiian and Réunion-like volcanoes. (a) The spreading model of Hawaiian volcanoes: a décollement, possibly activated by creeping cumulates, very active and persistent rift zones, and compression at the base of the edifice. (b) The stress permutation model of Réunion-like volcanoes: no basal creep, smaller magmatic system, intrusions alternatively captured into sill zones and diffuse rift zones (RZ), and intermittent compression in the upper part of the edifice. (Figure 15 in Chaput et al., 2014)

Dimensionless internal displacement, surface displacement, and slope changes associated with different types of subhorizontal fractures (dip = 10°): purely opened sheet intrusions (driving pressure Δσn), sheared sheet intrusions, and faults. The contour lines indicate the ground surface elevations. They are every 500 m (Figure 6 in Cayol et al., 2014)

Outer flank activity of Piton de la Fournaise