New evidence of CO₂ soil degassing anomalies on Piton de la Fournaise volcano and the link with volcano tectonic structures

Abstract

Piton de la Fournaise (PdF) is recognized as one of the world's most active volcanoes in terms of eruptive frequency and the substantial quantity of lava produced. Yet with the sole exception of rather modest intracrateric fumarole activity, this seems to be in contrast with an apparent absence of any type of natural fluid emission during periods of quiescence. Measurement campaigns were undertaken during a long-lasting quiescent period (2012)(2013)(2014) and just after a short-lived summit eruption (June 2014) in order to identify potential degassing areas in relation to the main structural features of the volcano (e.g., rift zones) with the aim of developing a broader understanding of the geometry of the plumbing and degassing system. In order to assess the possible existence of anomalous soil CO 2 flux, 513 measurements were taken along transects roughly orthogonal to the known tectonic lineaments crossing PdF edifice. In addition, 53 samples of gas for C isotope analysis were taken at measurement points that showed a relatively high CO 2 concentration in the soil.

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)

“…and vegetation cover. For comparison, the search for CO 2 anomalies performed by Liuzzo et al (2015) was performed with an average spacing of 100 m. The reported profiles represent the best choice to obtain long and high-resolution measurements with a nearly constant spacing. Field measurements were carried out during the eruptive phase of August 2015, while the more proximal GIT profile was measured in May 15, 2015 during a sequence of earthquakes whose hypocentres showed a progressive upward migration below the central area ( Lengliné et al, 2016), concomitant with CO 2 enrichment in the summit fumaroles emissions (Peltier et al, 2016).…”

“…1; Bachèlery, 1981;Chevallier and Bachèlery, 1981;Villeneuve and Bachèlery, 2006;Bonali et al, 2011;Liuzzo et al, 2015;Michon et al, 2015Michon et al, , 2016. The two most active of these are the SE and NE rift zones (SERZ and NERZ), which have been interpreted as shallow lateral pathways of magma initially injected below the central area.…”

“…The SERZ and NERZ are thought to be closely linked to the central shallow plumbing system of Piton de la Fournaise and to result from the seawards displacement of the steep eastern flank (Bonali et al, 2011;Michon et al, 2015 ). On the aseismic SERZ and NERZ, Liuzzo et al (2015) have reported high soil CO 2 emissions, possibly defining a secondary deep magma transfer especially along recently active zones or/and possible tectonic structures oriented N90° cutting the western flank.…”

“…The third and largest rift zone, the NWRZ, has been characterised by peripheral eruptions for at least 29 ky (McDougall, 1971; Liuzzo et al, 2015;Michon et al, 2015). Seismicity shallower than 11 km (bsl) mainly occurs below the central cone (Enclos Fouqué) and is related to the shallow plumbing system of Piton de la Fournaise.…”

“…At Piton de la Fournaise (La Réunion Island), diffuse flank CO 2 degassing is generally very weak (Seidel et al, 1988;Marty et al, 1993;Toutain et al, 2002;Liuzzo et al, 2015 ) and includes a significant biogenic component. This peculiar condition is explicable, most probably, by the tropical oceanic climate, which is marked by extreme precipitation rates and a high average temperature, allowing substratum degradation and fast vegetation development.…”