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)

• Published in: Journal of volcanology and geothermal research 2017-07, Vol.341, p.193-207
• Main Authors: Boudoire, G., Liuzzo, M., Di Muro, A., Ferrazzini, V., Michon, L., Grassa, F., Derrien, A., Villeneuve, N., Bourdeu, A., Brunet, C., Giudice, G., Gurrieri, S.
• Format: Article
• Language: English
• Subjects: Earth Sciences; Geochemistry; Geophysics; magma migration; photogrammetry; Sciences of the Universe; seismicity; Soil CO2 emissions; Volcanology; δ13C - isotope tracers
• ISSN: 0377-0273; 1872-6097
• DOI: 10.1016/j.jvolgeores.2017.05.026

Peripheral diffuse degassing of CO2 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 δ13C) overlap spatial distribution of hypocenters recorded shortly before and during volcano reactivation and allow discriminating a N135° degassing lineament, with a minimum length of 11km and 140±20m-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. •Multidisciplinary approach leading to the identification of magma pathways.•Volcano reawakening may be heralded by structure reactivation.•Identified degassing structures open prospects for volcano monitoring.•Laterally shifted deep magmatic plumbing system is confirmed at Piton de la Fournaise.