Investigating the deepest part of a volcano plumbing system: Evidence for an active magma path below the western flank of Piton de la Fournaise (La Réunion Island)

Abstract

Peripheral diffuse degassing of CO 2 from the soil occurs across the western flank of Piton de la Fournaise volcano (La Réunion Island, Indian Ocean) along a narrow zone. In this area, carbon isotopic analysis on soil gas samples highlights significant mixing between magmatic and organic end-members. The zones with the strongest magmatic signature (highest δ 13 C) overlap spatial distribution of hypocenters recorded shortly before and during volcano reactivation and allow discriminating a N135° degassing lineament, with a minimum length of 11 km and 140 ± 20 m-width. Such orientation is in accordance with that of an old dyke network along the rift zone and with N120-130° and N140-155° lineaments related to the inheritance of oceanic lithosphere structures. Our findings show that this N135° lineament represents a preferential magmatic pathway for deep magma transfer below the volcano flank. Moreover, spatial distributions of recent eccentric cones indicate a well-founded possibility that future eruptions may by-pass the shallow plumbing system of the central area of the volcano, taking a lateral pathway along this structure. Our results also confirm that Piton de la Fournaise activity is linked to a laterally shifted plumbing system and represent a major improvement in identifying the main high-risk area on the densely populated western flank of the volcano.

Integrating field, textural, and geochemical monitoring to track eruption triggers and dynamics: a case study from Piton de la Fournaise

“…From 2011, the deformation at PdF was constant with two distinct types of behaviour: (i) a summit contraction of a few centimetres every year ( Fig. 1d) and (ii) a preferential displacement of the east flank at a rate of 1-3 cm per year (Brenguier et al, 2012;Staudacher and Peltier, 2015). The background microseismicity was very low (less than five shallow events per day below volcano summit) and low-temperature summit intracaldera fumaroles emitted very little sulfur (H 2 S or SO 2 ) and carbon (CO 2 ) (Di .…”

Extensive CO2 degassing in the upper mantle beneath oceanic basaltic volcanoes: First insights from Piton de la Fournaise volcano (La Réunion Island)

“…l.) and is in accordance with most of the barometric data obtained on NWRZ eruptive products (Bureau et al, 1998;Boudoire, 2017). Based on the spatio-temporal location of recent seismic hypocenters, some authors have proposed that central crustal reservoirs are fed by lateral transfers of melts at mantle level below the NWRZ, starting from a 30 km-deep offset deep plumbing system located between PdF and Piton des Neiges volcanoes Boudoire et al, 2017aBoudoire et al, , 2017b. Interestingly, this zone located between both volcanic edifices is also set by the highest soil CO 2 fluxes, which contrasts with the weakness of inter-eruptive gas emissions in the central area (Liuzzo et al, 2015;Di Muro et al, 2016).…”

Complex structure of Piton de la Fournaise and its underlying lithosphere revealed by magnetotelluric 3D inversion

“…Earthquakes are observed from about 8 km in depth to the surface before and during volcanic crises with an overall lateral migration of the seismic swarms along 10-11 km, from the Plain des Sables toward the presently active area of Piton de la Fournaise. In addition, a high resolution survey of soil CO 2 emissions carried out on the western flank of Piton de la Fournaise (Boudoire et al, 2017) has evidenced that narrow zones of high fluxes are aligned along a well-defined N135° axis coincident with seismic swarms detected during the reawakening of the volcano (2014-2015). The authors have called this alignment the Songit Lineament (Fig.…”