Andrea Di Muro

The 2007 eruptions and caldera collapse of the Piton de la Fournaise volcano (La Réunion Island) from tilt analysis at a single very broadband seismic station

Seismic records from La Reunion Island very broadband Geoscope station are investigated to constrain the link between the 2007 eruptive sequence and the related caldera collapse of the Piton de la Fournaise volcano. Tilt estimated from seismic records reveals that the three 2007 eruptions belong to a single inflation-deflation cycle. Tilt trend indicates that the small-volume summit eruption of 18 February occurred during a phase of continuous inflation that started in January 2007. Inflation decelerated 24 days before a second short-lived, small-volume eruption on 30 March, almost simultaneous with a sudden, large-scale deflation of the volcano. Deflation rate, which had stabilized at relatively low level, increased anew on 1 April while no magma was erupted, followed on 2 April by a major distal eruption and on 5 April by a summit caldera collapse. Long-term tilt variation suggests that the 2007 eruptive succession was triggered by a deep magma input.

Magma Degassing at Piton de la Fournaise Volcano

Since about 1860 AD, magmatic gas release at Piton de la Fournaise volcano is very weak during intra-eruptive phases and essentially occurs during the relatively short-lived eruptions. Recent gas measurements performed during an eruption in October 2010, combined with detailed review of melt and fluid inclusion composition in magmas erupted over the past 50 kyrs, indicate that most PdF eruptions extrude magmas having variably degassed at shallow depth (P 1 kbar) and the shallow magmas, whose fluids are efficiently scrubbed by the hydrothermal system and the water table. Quantification of SO2 fluxes permits to track syn-eruptive magma ascent at shallow level (above sea level). Deeper exsolution of CO2 (below sea level) provides a potential long-term geochemical precursor for the detection of new magma recharges and volcano unrest.

Fifteen Years of Intense Eruptive Activity (1998–2013) at Piton de la Fournaise Volcano: A Review

Piton de la Fournaise (La Reunion Island) is amongst the most active volcanoes in the world, having had about 130 eruptions during the last century. Over the last 50 years it has produced 970 Mm3 of magma, at a mean eruption rate of 19.4 Mm3 per year, of which 489 Mm3 had been erupted over the last 15 years (at a rate of 32.7 Mm3 per year). This indicates a relative increase in its output. In this paper we present a detailed description of the high volcanic activity spanning the 1998–2013 period (eruptive precursors, location, characteristics and volume of emitted lavas, …). This period of high volcanic activity has been the subject of numerous studies that have led to significant advances in the knowledge of the shape and dynamics of the shallow plumbing system of the volcano.

Modeling the lava heat flux during severe effusive volcanic eruption: An important impact on surface air quality

The April 2007 eruption of Piton de la Fournaise, one of the most active volcanoes in the world, was the strongest eruption in recent decades with 230Mm3 of lava emitted and more 300KT of SO2 degased. The surface concentrations of SO2 have been measured by the ORA (Air Observatory of the Reunion Island) and showed that many stations exceeded the critic threshold for health. These high concentrations led to important health issues, accompanied by environmental and infrastructure degradations. Realized with MesoNH atmospheric model, our simulations show the transport of sulfur and his component between 2 April and 6 April 2007, with a focus on the influence of heat flow from lava. For this purpose, we have implemented ForeFire, a surface model initially realized to simulate forest fire, by adapting it to reproduce the dynamic of a lava flow. Thus, all flows (SO2, heat, vapor, CO2, CO) are triggered depending on its dynamic. With this first approach, our simulations reproduce quite faithfully the surface field observation of SO2 provides by ORA. Various sensitivity analyzes exhibit that volcano sulfur distribution was mainly controlled by the lava heat flow. Without heat flow parameterization, the surface concentrations are multiplied by a factor 30 compared to the reference simulation. Simulations also put in evidence that the 5 April, during the height of the eruption, changes in meteorological conditions, especially weakening of atmospheric boundary layer stability, led to various pollutants to be transported in higher altitude (8000m). The main consequence is the volcanic pollutants are transported off the east coast of Reunion Island.

Magma Paths at Piton de la Fournaise Volcano

Several patterns of magma paths have been proposed since the 1980s for Piton de la Fournaise volcano. Given the significant differences, which are presented here, we propose a reappraisal of the magma intrusion paths using a 17-years-long database of volcano-tectonic seismic events and a detailed mapping of the scoria cones. At the edifice scale, the magma propagates along two N120 trending rift zones. They are wide, linear, spotted by small to large scoria cones and related lava flows and involving magma resulting from high-pressure fractionation of ol ± cpx and presents an eruption periodicity of around 200 years over the last 30 kiloyears. The upper plumbing system originates at the base of the edifice below the Enclos Fouque caldera. It feeds frequent (1 eruption every 9 months on average), short-lived summit and distal (flank) eruptions along summit and outer rift zones, respectively. Summit rift zones are short and present an orthogonal pattern restricted to the central active cone of Piton de la Fournaise whereas outer rift zones extend from inside the Enclos Fouque caldera to the NE and SE volcano flanks. To sum up, rift zones of Piton de la Fournaise present strong geometrical and dynamical differences. On the one hand, the lower plumbing system feeds rift zones showing striking similarities to those developed in Hawaii during the alkaline postshield stage. On the other hand, the rift zones connected to upper plumbing system can be compared the rift system of Mount Etna, whose dynamics is know to be linked with the lateral displacement of the east flank.

Geology and Morphostructural Evolution of Piton de la Fournaise

The morphology of Piton de la Fournaise volcano results from the succession of construction, destruction and deformation processes that occurred since at least 530 ka. The chaotic surface of the gently dipping submarine flanks indicates that volcaniclastic deposits related to massive flank landslides and erosion cover most of the submarine flanks. Only a few seamounts like Cone Elianne and the submarine continuation of the rift zones are built by lava flows. In the subaerial domain, Piton de la Fournaise exhibits deeply incised canyons evidencing intense erosion and eastward verging scarps whose origin is still controversial. The different interpretations invoking flank landslides and/or summit collapse calderas are summarized. Geological data indicate a twofold construction of Piton de la Fournaise. Between 530 and 60 kyrs, the volcanic centre located in the current Plaine des Sables led to the building of the western part of the massif. The volcanic centre migrated eastwards to its current location, possibly at 60–40 kyrs. Then Piton de la Fournaise experienced caldera collapses and recurrent phreatomagmatic eruptions especially between 4880 and 2340 yr BP as evidenced by the Bellecombe ash deposit. Most of the recent volcanic activity is now currently focused restricted inside the Enclos Fouque caldera where lava flow accumulation and rare explosive events built the 400-m-high Central Cone.

Pre-historic (<5 kiloyear) Explosive Activity at Piton de la Fournaise Volcano

The characterization of the recent (<5 kiloyears) explosive activity and the research of violent paroxystic events over Piton de la Fournaise edifice has been performed through a drilling and excavation campaign supported by the integration of new radiocarbon ages to previous chronologic data. Fine grained “Bellecombe” phreatomagmatic ashes represent the product of the most violent explosive Piton de la Fournaise activity inside the investigated period. This activity results from a series of eruptions occurred over a time span much longer than previously thought. Anyhow, it represents the most traceable horizon (up to 13 km W-NW from the central cone) among the studied deposits and no other pyroclastic blanket exhibits a similar regional dispersion. The lack of a continuous lapilli/ash horizon from the proximal to distal areas points out that the lapilli cover on the volcano flank result of several local blankets linked to as many Hawaiian to Strombolian emission centers. As highlighted by new radiocarbon ages this kind of activity persisted along the N120 rift zone up to very recent times and ended probably just before the island’s colonization, leaving no trace in historical records. The maximum expected magmatic event (Chisny-type eruption) has therefore to be related to intense Hawaiian fountaining. Its dangerousness is restricted to a relatively brief distance from the source and a regional deposition is strongly unlikely. The hazard represented by this type of activity resides in the possible positioning of the vent close to inhabited areas and in the possible occurrence of repeated events with short but unpredictable time interval from one to the other. Forecasting the location of the future eccentric eruptions is thus of paramount importance to minimize the potential impact of mild explosive eruptions on the inhabitants and the infrastructures.

Petrological and Experimental Constraints on the Evolution of Piton de la Fournaise Magmas

This chapter outlines essential petrological features of Piton de la Fournaise magmas. The main characteristics of the different magma types, and of their components (mineral and glass phases) are detailed. The available geophysical and petrological informations on the structure of the feeding system are combined and the magmatic conditions (temperature, volatile concentrations, redox state) summarized. Experimental modelling of the magmatic evolution is limited by the presently available database which concerns volatile-free compositions mostly from Piton des Neiges.

Volcanological Map of the Plaine des Sables, Piton de la Fournaise

This detailed volcanological map of Plain des Sables (PdS) put in evidence the existence of three polygenetic centers (Demi Piton, Piton Chisny, and Piton Hauy) that developed in very recent times. This fact imply that PdS must be considered as one of the most active and potentially hazardous sectors of the Piton de la Fournaise volcano.