Structural control of collapse events inferred by self-potential mapping on the Piton de la Fournaise volcano (La Réunion Island)

Abstract

International audienceField surveys were performed on the terminal cone of Piton de la Fournaise in 2006 and 2008 to precisely map the self potential (SP) signal and determine the zonation of the hydrothermal activity both on the flanks of the cone and in the summit area, including inside the Bory and Dolomieu craters. SP maps inside the craters have been performed 8 months before the 5–7 April 2007 caldera collapse. Zonations appear both at the scale of the cone and of the summit and allow new interpretation of the electrical signal distribution on the terminal cone of Piton de la Fournaise. Superimposed to the SP maxima linked to the rift-zones, several areas of SP maxima associated with collapse structures have been detected: (1) in the summit area, the Bory and Dolomieu craters show the strongest SP values with amplitudes exceeding 2 V with respect to the base of the cone, and with a sharp lateral variation to the East, corresponding to the inner boundary of the Dolomieu caldera, collapsed on 5–7 April 2007, and (2) in the paleo pit craters surrounding the summit which show amplitudes similar to the Dolomieu–Bory craters. The analysis of the variations of the signal with time evi-dences a modification of the fluid flow pattern with a higher associated SP signature to the east in 2008. We interpret the amplification of fluid flow to the east in 2008 as a consequence of the eastward motion of the eastern flank of the volcano during the April 2007 eruption. The acquisition of SP data during two periods separated by the April 2007 eruption turns out to be a good opportunity to correlate the SP signal to the Piton de la Fournaise structure and to its evolution in term of hydrothermal and eruptive activity

Hydrothermal system of Central Tenerife Volcanic Complex, Canary Islands (Spain), inferred from self-potential measurements

“…Positive SP values are indeed detected in the outer parts of the NW rift zone, but they are readily explained by a combination of the topographic effect and the presence of a shallower water-table laterally confined by the dense web of mafic dykes reaching the surface at the rift, without need to invoke any hydrothermal activity. This absence of continuous hydrothermal activity from the summit of the rift zones is in contrast with what is known from other volcanic islands like Hawaii (Zablocki, 1976) or La Reunion island (Barde-Cabusson et al, 2012), where either shallow mafic magma reservoirs below rift systems or high magma extrusion rates and correspondingly long-lived thermal anomalies sustain active hydrothermal convection that is detected by continuous positive SP anomalies running from the summit towards the rift zone axis.…”

“…Hydrothermal systems can develop a strong coupling with the eruptive activity of their parent magmatic systems and sometimes the state of the hydrothermal system, its spatial dimensions and the intensity of the heat transfer can be used as a volcano monitoring tool (Aubert et al, 2008;Gaudin et al, 2013). The lateral extension and the geometry of a hydrothermal system are highly variable, depending on diverse factors, both internal to the volcanic system, like structural boundaries (caldera, craters, regional faults, weakness areas) and also external, like the pattern and magnitude of meteoric groundwater recharge by rain and snow Tort and Finizola, 2005;Barde-Cabusson et al, 2012;Peltier et al, 2012).…”

Electric potential anomaly induced by humid air convection within Piton de La Fournaise volcano, La Réunion Island

“…However, surprisingly, SP amplitudes as high as 3 V are observed between the periphery and the terminal cone (Michel and Zlotnicki, 1998;Barde-Cabusson et al, 2012) (Fig. 2).…”

“…SP anomalies have been observed on active volcanoes with an amplitude ranging from a few hundreds millivolts up to several volts (Michel and Zlotnicki, 1998;Finizola et al, 2004;Aizawa, 2008;Barde-Cabusson et al, 2012;Brothelande et al, 2014). Saturated ground water flow is usually considered as the main process (so-called electrokinetic phenomenon) inducing the SP signal (Malengreau et al, 1994;Michel, 1998;Aubert et al, 2000;Finizola et al, 2004;Ishido, 2004;Bedrosian et al, 2007).…”

Lead isotopes behavior in the fumarolic environment of the Piton de la Fournaise volcano (Réunion Island)

“…Hydrothermal activity seems to be confined to the summit crater, under which a low-resistivity zone was identified (Lénat et al, 2000). Lower hydrothermal activity has also been evidenced with self-potential technique along the North-South rift zone crossing the summit area (Barde-Cabusson et al, 2012). Piton de la Fournaise lacks persistent and localized degassing activity, so that sampling of magmatic gas is systematically hampered by atmospheric contamination.…”