Explosive activity of the summit cone of Piton de la Fournaise volcano (La Réunion island): A historical and geological review

Abstract

International audienceSummit explosive activity and collapses that form pit craters and calderas represent major volcanic hazards on a dominantly effusive, frequently active volcano like Piton de la Fournaise. Only three summit collapse events (1986, 2002, 2007) have been recorded since the foundation of the Piton de la Fournaise volcano observatory (OVPF) in 1979, and two of them (1986 and 2007) were associated with weak phreatic activity. At Piton de la Fournaise, the normal explosive activity consists of short-lived and mild (< 20 m-high) lava fountains, which quickly evolve into strombolian activity during the eruptions. Based on comprehensive literature review and high-resolution image analysis of surface outcrops and summit caldera walls, we reconstructed the time distribution of recent explosive events (phreatomagmatic; phreatic) and their link with summit collapses and lateral (flank) effusive eruptions. In historical time (post-1640 CE), we recognise two main clusters of explosive events. Frequent and violent phreatomagmatic to phreatic explosions occurred during the oldest cluster (1708–1878) and alternated with long-lasting periods (years to decades) of summit effusive activity. In contrast, scarce, and on average, weak explosions occurred during the youngest cluster (1897–2012), when discrete and short-lived (< 6 months) effusive eruptions represent the main eruptive dynamics. Historical summit collapses (pit craters and caldera), all localised at the top of the summit cone, were related to voluminous lateral eruptions and were followed by a significant decrease in eruptive rate. However, magma draining during lateral eruptions was not systematically associated with summit collapses or explosions. The long-lasting occurrence of magma at very shallow depth below the volcano summit, followed by a rapid lateral drainage, apparently represents a critical condition favouring magma–groundwater interaction to produce explosive activity. The prehistoric growth of the Piton de la Fournaise summit cone results chiefly from long-lasting to continuous activity, centred below its western side (Bory crater containing lava lakes). High lava fountains, long-lasting effusive activity, lava lakes, ash plumes and block ejections were common types of eruptive dynamics in the historical past, between 1640 and 1878. In this perspective, short-lived, small volume eruptions and long pauses, up to six years, during the last century of activity of Piton de la Fournaise can be considered as a lull, despite the high frequency of eruption (1 eruption/9 months on average). Temporal and spatial variations in recurrence rate and eruptive dynamics of basaltic volcanism, such as those recognised at Piton de la Fournaise, should be considered in the formulation of hazard assessments and in the interpretation of precursory patterns

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)

“…PdF is one of the world's most active volcanoes, averaging one eruption every nine months since 1930 ( Peltier et al, 2009;Roult et al, 2012). Recorded observations since 1640 show that eruptions have been mostly restricted within the seawards oriented, horseshoe-shaped, open Enclos Fouqué caldera ( Villeneuve and Bachèlery, 2006;Michon et al, 2013) whose formation occurred between 5465 and 2971 calendar years BP (Bachèlery, 1981;Upton et al, 2000;Ort et al, 2016). Seismic activity within this central area is restricted to a crustal depth range shallower than 8-9 km bsl (Battaglia et al, 2005;.…”

Effusive crises at Piton de la Fournaise 2014–2015: a review of a multi-national response model

“…Large-volume eruptions have been documented, with that of April 2007 ), being of quite shortduration (less than 1 month). Effusive events can also be long-lasting (several years), where decade-long phases of continuous activity, punctuated by short-lived explosive events, have been observed in the geological record (Peltier et al 2012;Michon et al 2013). In 2007, the most voluminous eruption of historical times occurred at an altitude of 570 m above sea level, 400 m north of the southern wall of the Enclos Fouqué caldera.…”

First results of the Piton de la Fournaise STRAP 2015 experiment: multidisciplinary tracking of a volcanic gas and aerosol plume

“…Even if phreatic and phreatomagmatic eruptions have been described in the 18th and 19th centuries Michon et al, 2013), since the end of the 18th century the eruptive activity has mostly consisted of dominantly effusive or weakly explosive eruptions. A characteristic of Piton de la Fournaise eruptions consists of the opening of en echelon fissures, with an activity rapidly declining in intensity and focusing on the lowest point of the feeding fissure and forming a small cone from the accumulation of ejecta (Hibert et al, 2015).…”

“…The 2015 STRAP experiment has been performed on the Piton de la Fournaise (PdF) volcano and has benefited of a strong cross-disciplinary collaboration between European scientists from 10 laboratories (France, Italy, Sweden, Cyprus). Piton de la Fournaise was selected as it is a well-known, very active volcano (four eruptions in 2015) and emits lava flows and gas plumes carrying negligible amounts of ash (Roult et al, 2012;Michon et al, 2013). Very few data exist on the composition and fluxes of high-temperature volcanic gases emitted by PdF eruptions (see Di Muro et al (2016a) for a recent review).…”