Transient self-potential anomalies associated with recent lava flows at Piton de la Fournaise volcano (Réunion Island, Indian Ocean)

International audienceSelf-potential signals are sensitive to various phenomena including ground water flow (streaming potential), thermal gradients (thermoelectric potential), and potentially rapid fluid disruption associated with vaporization of water. We describe transient self-potential anomalies observed over recent (< 9 years) lava flows at Piton de la Fournaise volcano (Reunion Island, Indian Ocean). Repeated self-potential measurements are used to determine the decay of the self-potential signals with time since the emplacement of a set of lava flow. We performed a 9 km-long self-potential profile in February 2004 in the Grand Brûlé area. This profile was repeated in July–August 2006. The second repetition of this profile crossed eight lava flows emplaced between 1998 and 2005 during seven eruptions of Piton de la Fournaise volcano. The self-potential data show clear positive anomalies (up to 330 mV) and spatially correlated with the presence of recent lava flows. The amplitude of the self-potential anomalies decreases exponentially with the age of the lava flows with a relaxation time of not, vert, similar 44 months. We explain these anomalies by the shallow convection of meteoric water and the associated streaming potential distribution but we cannot exclude possible contributions from the thermoelectric effect and the rapid fluid disruption mechanism. This field case evidences for the first time transient self-potential signals associated with recent volcanic deposits. It can be also a shallow analogue to understand the variation of self-potential signals in active geothermal areas and transient self-potential signals associated with dike intrusion at larger depths. The empirical equation we proposed can also be used to diagnose the cooling of recent lava flow on shield volcanoes

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

Field 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 evidences 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. © 2011 Elsevier B.V.The field work was supported by The Université de la Réunion (BQR 2005–2006).Peer Reviewe

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

Field 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 8months 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 2V 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 evidences 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

Transient self-potential anomalies associated with recent lava flows at Piton de la Fournaise volcano (Réunion Island, Indian Ocean)

International audienceSelf-potential signals are sensitive to various phenomena including ground water flow (streaming potential), thermal gradients (thermoelectric potential), and potentially rapid fluid disruption associated with vaporization of water. We describe transient self-potential anomalies observed over recent (< 9 years) lava flows at Piton de la Fournaise volcano (Reunion Island, Indian Ocean). Repeated self-potential measurements are used to determine the decay of the self-potential signals with time since the emplacement of a set of lava flow. We performed a 9 km-long self-potential profile in February 2004 in the Grand Brûlé area. This profile was repeated in July–August 2006. The second repetition of this profile crossed eight lava flows emplaced between 1998 and 2005 during seven eruptions of Piton de la Fournaise volcano. The self-potential data show clear positive anomalies (up to 330 mV) and spatially correlated with the presence of recent lava flows. The amplitude of the self-potential anomalies decreases exponentially with the age of the lava flows with a relaxation time of not, vert, similar 44 months. We explain these anomalies by the shallow convection of meteoric water and the associated streaming potential distribution but we cannot exclude possible contributions from the thermoelectric effect and the rapid fluid disruption mechanism. This field case evidences for the first time transient self-potential signals associated with recent volcanic deposits. It can be also a shallow analogue to understand the variation of self-potential signals in active geothermal areas and transient self-potential signals associated with dike intrusion at larger depths. The empirical equation we proposed can also be used to diagnose the cooling of recent lava flow on shield volcanoes