Control of source fertility on the eruptive activity of Piton de la Fournaise volcano, La Réunion

Abstract

The eruptive activity of basaltic hotspot volcanoes displays major fluctuations on times scales of years to decades. Theses fluctuations are thought to reflect changes in the rate of mantle melt supply. However, the crustal filter generally masks the mantle processes involved. Here, we show that the cyclic and generally increasing activity of the Piton de la Fournaise volcano (La Réunion) since the mid 20th century is tightly linked to the fertility of its source, as recorded by 87Sr/86Sr and incompatible trace elements ratios of lavas. We identify a twofold control of source fertility on eruptive activity: melt extraction from fertile, incompatible element-enriched veins initiates decadal-scale eruptive sequences, so that vein distribution in the plume source directly controls the cyclic activity. Indirectly, reactive flow of enriched melts increases mantle porosity and promotes melts extraction from the peridotite matrix. This process is thought to have caused a fourfold increase in magma supply between 1998 and 2014 at Piton de la Fournaise, and could also explain magma surges at other frequently active hotspot volcanoes, such as Kilauea, Hawaii. The short-term eruptive activity of hotspot volcanoes appears to be ultimately linked to the distribution and size of lithological heterogeneities in mantle plumes.

Combining InSAR and GNSS to Track Magma Transport at Basaltic Volcanoes

“…GNSS stations installed in this area after the eruption, combined with InSAR monitoring, indicate an ongoing eastward motion of about ∼2 cm·year −1 [35]. A new eruption cycle started in June 2014 [36,37]. Since then 16 eruptions have occurred on the flanks of the cone, inside the caldera-shaped depression including the May 2016 eruption studied here.…”

Lava flow hazard map of Piton de la Fournaise volcano

“…The inventory of all eruptions since record allows (beginning of the 18 th century since the first confidently dated eruption in 1708) has been detailed by several studies (Michon et al, 2013;Morandi et al, 2016;Villeneuve and Bachèlery, 2006). By compiling these studies and the exhaustive record since establishment of the OVPF (Peltier et al, 2009;Roult et al, 2012;Vlastélic et al, 2018), as well as recent OVPF reports (ISSN 2610-5101), we estimate that Piton de la Fournaise had about 250 eruptive events over a period of three centuries. About 95 % of these have occurred inside the Enclos (Table S1).…”

“…They may end with a large-volume, distal eruption at a distance of more than 4 km from the summit, as was the case in 2007, or an Hors Enclos eruption, as was the case for the cycle that ended in 1977. In addition to these superficial cycles, lava composition seems to be affected by cyclic changes in the "fertility" of the source magma as observed since 1930, the date since which the petrology of the volcanic products has been well documented (Vlastélic et al, 2018). These deep source-related cycles are typically of longer duration (20-30 years) and are characterized by a continuous increase followed by a continuous decrease in source fertility, until a minima is reached which marks the end of a cycle and the beginning of a new one (Vlastélic et al, 2018).…”

“…In addition to these superficial cycles, lava composition seems to be affected by cyclic changes in the "fertility" of the source magma as observed since 1930, the date since which the petrology of the volcanic products has been well documented (Vlastélic et al, 2018). These deep source-related cycles are typically of longer duration (20-30 years) and are characterized by a continuous increase followed by a continuous decrease in source fertility, until a minima is reached which marks the end of a cycle and the beginning of a new one (Vlastélic et al, 2018). High-volume distal eruptions associated to crater collapse occurring in 1931-35, 1961, 1986 and 2007 mean that three-quarters of such cycles are characterized by such "atypical", low flank events, where they typically occur just after the peak of source fertility (Derrien, 2019).…”

“…For any eruption at Piton de la Fournaise a fissure typically opens perpendicular to the slope, the magma erupts uniformly along the fissure to feed several lava flow units simultaneously to form a flow field of many overlapping flow units. In such a case we count only a single flow, the longest, and do not consider all units that comprise the compound lava flow field in the data base (e.g., Walker, 1973). In the case where there is a pause in the eruption and new flows are emitted in a second phase of activity, then the longest flow after the hiatus is also counted, so that the eruption has two flows associated with it in the data base.…”