Andrea Morandi

Andrea Di Muro

Claudia Principe
email: c.principe@igg.cnr.it

Laurent Michon

Gabrielle Leroi

Francesco Norelli

Patrick Bachèlery

Á G Leroi

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.

Introduction

Piton de la Fournaise (PdF) is one of the most active basaltic intra-plate volcanoes. Even if the number of identified eruptive events depends on the completeness of written records (Lénat 2016, Chap. 1), at least 238 eruptions have been recognized since the second half of the 17th century, when permanent settlement on the island began [START_REF] Ludden | Eruptive patterns for the volcano Piton de la Fournaise, Reunion Island[END_REF][START_REF] Bachèlery | Le Piton de la Fournaise (Ile de la Réunion). Etude Volcanologique, Structurale et Pétrologique[END_REF]; Lénat and Bachèlery 1988;[START_REF] Stieltjes | A statistical and probabilistic study of the historic activity of the Piton de la Fournaise, Réunion Island, Indian Ocean[END_REF][START_REF] Roult | A new comprehensive classification of the Piton de la Fournaise activity spanning the 1985-2010 period. Search and analysis of short-term precursors from a broad-band seismological station[END_REF][START_REF] Muro | Evaluation de l'alea volcanique a La Réunion[END_REF][START_REF] Michon | Explosive activity of the summit cone of Piton de la Fournaise volcano (La Réunion island): a historical and geological review[END_REF]. Since the establishment of permanent monitoring networks, coinciding with the foundation of Piton de la Fournaise Observatory (OVPF/IPGP) in 1979, there have been 61 instrumentally recorded eruptions. During the last 100 year, the average eruptive rate has been of about 1 eruption every 10 months and the longest eruptive pauses have occurred in recent times (1966-1972; 1992-1998) and have lasted up to 6 years. During recorded history, most of the eruptive vents were located close to the PdF central cone and more generally inside the horseshoe-shaped Enclos Fouqué depression, which encloses it. Only rare lateral eruptive fissures opened outside the Enclos Fouqué, along the NE and SE rift zones (Michon et al. 2016, Chap. 7;Staudacher et al. 2016, Chap. 9). Since human settlement on the island on 1638 CE, eruptive events have not been recorded along the third and largest NW rift zone materialized by a N 120°trending cone alignment. However, the first settlements on La Réunion were located on the opposite coast of the island (NW coast) in respect to PdF. The corollary is that written records cover only a very short period at La Réunion, reliable written reports on PdF activity dating only back to 1754 CE [START_REF] Michon | Explosive activity of the summit cone of Piton de la Fournaise volcano (La Réunion island): a historical and geological review[END_REF]. Therefore, it is of paramount importance to assess volcanic hazard over a period long enough to be representative of the variability in eruptive dynamics of PdF.

Nowadays, the island accounts for more than 830,000 permanent residents and ca. 470,000 tourists per year. Densely populated cities and villages are widespread on the whole active volcanic massif and progressively develop towards the most active volcanic zone. In recent times, effusive eruptions have periodically affected important infrastructure like the eastern national road, buildings and farmlands. In 1977 and 1986, the volcanic activity produced the opening of lateral eruptive fissures emitting lava that flowed through inhabited areas (Piton Sainte-Rose and Tremblet, respectively) up to the sea-shore [START_REF] Delorme | March 1986 eruptive episodes at Piton de la Fournaise volcano (Réunion Island)[END_REF][START_REF] Kieffer | Une éruption inhabituelle (Avril 1977) du Piton de La Fournaise (Ile de La Réunion): ses enseignements volcanologiques et structuraux[END_REF].

Recent review of historic reports has revealed that weak to mild phreatic and phreatomagmatic ash plumes (the most violent corresponding to the 1860 CE eruption) repeatedly punctuated the dominantly effusive activity of the central cone, spreading fine ash on the volcano edifice and sometimes over most of La Réunion Island [START_REF] Bachèlery | Le Piton de la Fournaise (Ile de la Réunion). Etude Volcanologique, Structurale et Pétrologique[END_REF][START_REF] Villeneuve | Revue de la typologie des éruptions au Piton de La Fournaise, processus et risques volcaniques associés[END_REF][START_REF] Roult | A new comprehensive classification of the Piton de la Fournaise activity spanning the 1985-2010 period. Search and analysis of short-term precursors from a broad-band seismological station[END_REF][START_REF] Michon | Explosive activity of the summit cone of Piton de la Fournaise volcano (La Réunion island): a historical and geological review[END_REF]. Dispersal of Pele's hairs over the whole island can also occur, as in 1939 and in 2007 [START_REF] Michon | Explosive activity of the summit cone of Piton de la Fournaise volcano (La Réunion island): a historical and geological review[END_REF]. More violent explosive phreatic to phreatomagmatic eruptions of PdF have traditionally been related to major old caldera forming events contributing to the formation of the Enclos Fouqué caldera. The Bellecombe Ash unit would account for such paroxysmal events around 4175-3200 BP [START_REF] Bachèlery | Le Piton de la Fournaise (Ile de la Réunion). Etude Volcanologique, Structurale et Pétrologique[END_REF]Mohamed-Abchir 1996). This chapter reviews the dynamics of pre-historic eruptions of PdF, whose age is comprised between the Bellecombe Ash unit and the recorded history. Magmatic explosive activity, like violent strombolian or subplinian events, cannot be a priori discarded even for a basaltic volcano in an intraplate environment. Even if effusive or mild explosive dynamics of Strombolian and Hawaiian types characterize the basaltic volcanic activity, it has been since long recognized that mafic magmas can produce violent explosive events, with ash columns up to 30 km high and their products spreading over an area of tens to more than 1000 km 2 (MacDonald 1972; [START_REF] Arrighi | Violent strombolian and subplinian eruptions at Vesuvius during post-1631 activity[END_REF][START_REF] Houghton | The influence of conduit processes on changes in style of basaltic Plinian eruptions: Tarawera 1886 and Etna 122 BC[END_REF][START_REF] Sable | Changing conditions of magma ascent and fragmentation during the Etna 122 BC basaltic Plinian eruption: evidence from clast microtextures[END_REF][START_REF] Sable | Eruption mechanisms during the climax of the Tarawera 1886 basaltic Plinian inferred from microtextural characteristics of deposits[END_REF][START_REF] Pioli | Explosive dynamics of violent strombolian eruptions: the eruption of Parícutin volcano 1943-1952 (Mexico)[END_REF][START_REF] Andronico | Shifting styles of basaltic explosive activity during the 2002-03 eruption of Mt. Etna. Italy[END_REF][START_REF] Wong | The middle scoria sequence: a Holocene Subplinian and of Okmok volcano, Alaska[END_REF]. The possible occurrence of such kind of events has thus motivated the recent re-assessment of volcanic hazard at La Réunion (Di [START_REF] Muro | Evaluation de l'alea volcanique a La Réunion[END_REF]. In this chapter, we address this issue by integrating previous and new stratigraphic and chronologic data obtained on stratigraphic sections and shallow drillings (<10 m).

Wind Distribution Over La Réunion Island and Microstratigraphic Drilling Strategy

Wind direction and strength play an important role on the regional distribution of pyroclastic products dispersed by vertical plumes carrying ash and lapilli. This is particularly true for the finest particles that can be carried tens to hundreds of kilometers away from the eruptive source. The main synoptic winds over La Réunion Island are the Trade winds that blow northwestwards dominating the air circulation at ground level [START_REF] Trenberth | The mean annual cycle in global ocean wind stress[END_REF]). Local breezes effects become more influent mostly in downwind and protected areas, where the surface winds are weaker [START_REF] Lesouëf | Numerical simulations of local circulations and pollution transport over Reunion Island[END_REF].

The vertical winds distribution over La Réunion shows a marked inversion of their direction at an altitude of about 3000-4000 m asl [START_REF] Taupin | Tropospheric ozone above the southwestern Indian Ocean is strongly linked to dynamical conditions prevailing in the tropics[END_REF], depending on the season. The dispersion of pyroclasts is therefore strongly controlled by the height of the eruptive column. Examples are given by the ash and aerosol plumes generated during the April 2007 eruption, when an initial westward spreading of small ash and gas plumes was followed by a clockwise rotation toward N and NE sectors as the aerosol plume exceeded 4 km height [START_REF] Tulet | Large scale modeling of the transport, chemical transformation and mass budget of the sulfur emitted during the eruption of April 2007 by the Piton de la Fournaise[END_REF]. Ash dispersal during recent phreatomagmatic explosive eruptions (e.g. 1860 CE) confirms this trend and suggests even the possibility of a splitting of the eruptive columns [START_REF] Hugoulin | Dernière éruption du volcan de l'île de la Réunion (19 mars 1860)[END_REF][START_REF] Villeneuve | Revue de la typologie des éruptions au Piton de La Fournaise, processus et risques volcaniques associés[END_REF]. In agreement with this winds pattern, only sparse low amounts of basaltic shards, possibly attributed to PdF explosive events, were identified during the last 30 k year in a deep-sea marine core located south of the volcano edifice [START_REF] Fretzdorff | Explosive activity of the Reunion Island volcanoes through the past 260,000 years as recorded in deep-sea sediments[END_REF][START_REF] Sisavath | Processes controlling a volcaniclastic turbiditic system during the last climatic cycle: example of the Cilaos deep-sea fan, offshore La Réunion Island[END_REF]. Consequently, we performed in 2011 new microstratigraphic drillings and surface outcrops descriptions along a N-NW axis, between the proximal area (Plaine des Sables, about 5 km from the central cone) and the distal area (Grand Étang, 18 km NW from the summit vents), passing through the N120 rift zone. As a whole, 30 outcrops were described and 5 drillings were performed (Fig. 8.1).

The investigation of the spatial distribution of pyroclastic deposits must take carefully into account their potential preservation over the territory. This is particularly true in the tropical environment of La Réunion where a steep, pronounced topography is associated with extreme weather conditions (up to 6 m of rain per year and wind speed up to 250 km/h; Météo France source). Such a natural background produces a high rate of removal and reworking especially on the incoherent and easy-erodible pyroclastic sediments. The preservation potential of loose lapilli fallouts or thin ash layers (typical of small eruptions or distal outcrops) is therefore very low. As an example, the 1-2 cm-thick ash deposit from the 1986 Dolomieu phreatic explosion on the slopes of the summit cone of PdF was completely removed in less than one week, after two rainy days. In order to overcome these severe constraints, we selected low-energy sedimentation environments as drilling sites. This condition is better achieved in the endorheic volcanic lakes where the sedimentation is a quite sporadic event [START_REF] Principe | Metodologia innovativa di carotaggio microstratigrafico: esempio di applicazione alla tefrostratigrafia di prodotti vulcanici distali[END_REF][START_REF] Principe | Finding distal Vesuvius tephra at the borders of Lago Grande di Monticchio. In: AF shallow coring system micro-cores[END_REF]. In these setting, the deposition of tephra is limited to primary fallout deposits and the reworking is restricted to the bank's material. At La Réunion, this kind of sampling point is represented by intracrateric ponds on the top of strombolian cones spotted over the territory. On the oter hand, we have to stress that the volume of these permanent ponds/lakes is highly sensitive to the alternation of extreme pluviometric conditions and dryer periods. In other terms the sedimentation conditions are never optimal. To reach the selected locations, we used a portable drilling system (AF topcore 40 modified; Fig. 8.2a, b), able to produce 10 m long continuous and undisturbed micro-cores [START_REF] Principe | Metodologia innovativa di carotaggio microstratigrafico: esempio di applicazione alla tefrostratigrafia di prodotti vulcanici distali[END_REF]). This method is able to avoid the loss of information even for very thin layers, due to the presence of a textile sheet around the core (Fig. 8.2c). Wherever possible, the condensed tephra sequences, which sediment on the lakes shores, are drilled in order to reach the maximum length of tephra record with the minimum coring depth [START_REF] Principe | Finding distal Vesuvius tephra at the borders of Lago Grande di Monticchio. In: AF shallow coring system micro-cores[END_REF]. Thanks to the broad spreading of the grey, fine-grained Bellecombe Ash falls and to their peculiar mineral assemblage, i.e. abundant pyroxene + olivine crystals together with gabbro fragments and rare quartz crystals, they represented a perfect stratigraphic marker to identify tephra sequences younger than ca. 4000 year in the proximal-medial areas of the volcano.

In the Grand Étang distal drilling (GDE; Table 8.2) two units of fine ashes overly the proximal facies of a scoria cone, they contain a variable amount of granule to pebble-size clasts, the lower unit is characterized by the presence of organic matter. In the middle sector, Piton de l'Eau core (PDE2; Table 8.3) shows, within the scoria cone edifice (represented by the lower poorly sorted breccia), the presence of fine-grained deposits related to a reddish ashy paleosol containing organic matter and an upper stratigraphic succession of ashes which includes the Bellecombe Ash unit. Piton dans le Bout core (PLB; Table 8.4) is instead made of six units, of approximately alternating lapilli and ash beds. Bellecombe Ash unit underlies the uppermost black lapilli bed. We here stress that the "Bellecombe ash unit" group a sequence of events spanning about 2 millennia. The cpx-gabbro rich "Bellecombe ashes" cropping out in the Piton de l'eau-Piton dans le Bout area has been dated at 3735 ± 90 and 3715 ± 30 BP (Table 8.1). Younger ages in the range 3110 ± 30 BP-3060 ± 35 have been obtained for the uppermost beds of the "Bellecombe ash unit" along the Langevin plateau (Table 8.1). Notably, the ages of the lowermost beds in the "Bellecombe unit" cropping out in the proximal-medial area are somewhat older (4880 ± 35 BP; 4175 ± 145 BP; Table 8.1) than the uppermost beds, which attain the medial and distal sectors.

In the proximal sector, the two cores of the Plaine des Sables (PDS2 and PDS1; Tables 8.5 and 8.6) show, above the Bellecombe Ash unit, the presence of a black, glassy, and largely reworked lapilli sequence, which is intercalated with thin lava flows when approaching the Piton Chisny cone. In Tables 8.2, 8.3, 8.4, 8.5 and 8.6 (continued) a synthesis of all macroscopically and microscopically performed observations performed on drilling cores is presented.

In order to better constrain the explosive activity and the stratigraphic correlations in the N120 rift zone, the excavation of about 30 tephra sections has been performed in the proximal and middle sector of the volcano. It leads to the identification of several, spatially limited, lapilli deposits, and of three major tephra sequences, respectively in the Piton de Partage, Plaine des Sables, and Plaine des Remparts sectors (Fig. 8.1). These three sequences are described in the following.

The Partage Tephra

The "Partage Tephra" (Fig. 8.3) is here defined for the first time. It consists in a <1.5 m thick sequence of ash, lapilli and scoria beds that drape almost continuously the northern wall of the Enclos Fouqué caldera. The sequence attains the maximum thickness close to the northern caldera rim, thins out quickly when moving westward in the Plaine des Sables and is not observed in the Fond de la Rivière de l'Est, neither in more distal areas, as on the Plaine des Remparts plateau. The tephra sequence underlies the modern soil and has been divided in three units (U1; U2; U3 from base to top), on the basis of grain size, componentry and 14 C age. This tephra sequence was initially included in the "Bellecombe ash unit", but it results to be younger. Thin, usually <2 cm-thick, laterally continuous charcoal-rich layers are widespread inside the "Partage Tephra" sequence. The lowermost layer (CC0: 2855 ± 35 BP) occurs in the middle of Unit 1, while the others, CC1 and CC2, occur respectively at the base of Unit 2 (CC1: 2340 ± 30 BP) and of Unit 3 (CC2: 2140 ± 35 BP) (Table 8.1).

Near the Enclos Fouqué cliff, Unit 1 (U1) overlies a thin, usually <0.5 m thick bed of matrix-supported breccia containing scattered angular decimeter-sized lithic clasts ("Bellecombe breccia" sensu [START_REF] Bachèlery | Le Piton de la Fournaise (Ile de la Réunion). Etude Volcanologique, Structurale et Pétrologique[END_REF]. In more distal areas, Unit 1 often overlies older lavas. In 8.1). Average grain size distribution for each Unit is plotted as histogram. The matrix-supported breccia underlying the "Partage Tephra" sequence is attributed to the "Bellecombe Unit" the most proximal outcrops, Unit 1 groups at least four cm thin ash layers, whose maximum global thickness (≈30 cm) is observed close to Piton de Partage site. Piton de Partage scoria cone lies below Bellecombe breccia and "Partage" ashes. U1 ashes are brown to pink colored, fine grained (Md φ < -1.5 φ) and poorly sorted (σ φ = 1.5-2 φ) (Fig. 8.3). The ash layers are composed of minor highly fluidal glassy juvenile clasts in a volumetrically dominant matrix formed by variably altered lava fragments, possible small gabbro clasts, olivine crystals and rare euhedral quartz and magnetite (mostly in the lowermost layers). Similarities (in terms of grain size and componentry) between Unit 1 of the "Partage Tephra" and the (older) "Bellecombe Ash unit" suggest the possibility of an analogous mechanism at the origin of these deposits.

Unit 2 (U2) is a grey homogeneous lapilli and ash bed (Md φ = -1 φ), moderately sorted (σ φ = 1 -1.5 φ), with a high amount of dense clasts (mmto cm-sized grey lava fragments) (Fig. 8.3). Coarse fragments are dispersed in a fine-grained ash matrix containing olivine crystals and rare fluidal glassy fragments, whose amount increases towards the top of the bed. Bed thickness changes between 6 and 12 cm along the outcrop area.

Unit 3 (U3) consists of two scoria-rich beds. In the lower and thinner bed (<5 cm thick), reddish scoriae are supported by an ashy matrix. The upper main bed is a clast-supported deposit of mm-to cm-sized, reddish, variably altered scoriae with a moderate to low amount of crystals and lithic fragments. The bed is weakly normally graded (Md φ = -3 to -2 φ; σ φ = 1 -2 φ). The amount of free olivine crystals increases from the base to the top of the bed. The maximum thickness (1 m) is observed on the Enclos Fouqué wall located in front of the Formica Leo cone and decreases quickly moving away from this location, suggesting a quite narrow isopachs distribution. At Piton de Partage, the U3 thickness is about 35 cm.

The thickness distribution of the "Partage Tephra" sequence strongly supports the emission from one or more sources located close and (at least for U1 and U2 eruptions) inside the Enclos Fouqué. Eruptive dynamics possibly evolve from phreatomagmatic in the lowermost units (U1 and U2) to magmatic in the upper one (U3). U2 bed drapes the inner cliffs of Enclos Fouqué and gives a minimum age to the formation of this depression.

The Plaine des Sables Black Tephra

The black pyroclastic blanket forming the surface of large part of the Plaine des Sables consists mainly of very fresh and vesicular, fine to medium achnelith and black lapillis, which cover the areas surrounding between Piton Chisny and Piton Haüy cones. We have referred to this deposit as "Black Tephra" unit. It shows a maximum thickness of about 2.5 m in the area between Piton Chisny and Demi-Piton cones, near the NW foot of Piton Chisny edifice (Fig. 8.4). The deposit is absent on the Enclos Fouqué rim, while it is still present, although less than 10-20 cm thick, on the west edge of the Plain des Sables. In the proximal area, the "Black Tephra" sequence is a crudely stratified, well-sorted lapilli bed. Locally, a thin and coarse ash layer can be observed at its base (S13 and S20) that vanishes quickly when moving outside the main dispersal axis. In PDS2 core the basal ash layer is almost absent. In the proximal facies, the S20 section shows the presence of some spatter bomb layers. The distal facies (S3 section) is instead characterized by a basal coarse ash, a middle well sorted lapilli body, and a lapilli and ash top layer. Whereas not overlain by lavas, the deposit is often largely reworked (as in PDS1 and PDS2). In the ash fraction, olivine is the only mineral phase. Moving northwards in the Plaine des Sables, the Chisny black lapilli layer overlies the yellowish lapilli layer related to Piton Haüy activity. A dm to m thick bed of reworked ash and lapillis occur between them.

3.3

The "Red Tephra"

In the Plaine des Remparts area, the most widespread deposit consists in a bed of reddish glassy fluidal scoriae, here named "Red Tephra" unit, cropping out between Piton de l'Eau cone and Commerson crater. Maximum thickness (up to 2.5 m) is observed close to Piton des Cailles. Near Piton des Tangues, the fall bed is separated by a decimeter-thick black soil from the underlying Bellecombe Ash unit. The Red Tephra is restricted to the middle-distal sectors and is not observed in the proximal area of Plaine des Sables. As a whole, this unit has not been characterized yet and the source vent is unknown.

4 Frequency of PdF Explosive Activity During the Last 4000 Years

Available ages of PdF pre-historic volcanic events, together with new 14 C dating (Centre de Datation par le Radiocarbone, University Lyon 1), are here reviewed in order to identify the main periods of recent explosive volcanic activity (Table 8.1).

The main tephra identified all around the Enclos Fouqué is the "Bellecombe Ash unit". It corresponds to a complex sequence of ash, crystal and lithic-rich deposits [START_REF] Bachèlery | Le Piton de la Fournaise (Ile de la Réunion). Etude Volcanologique, Structurale et Pétrologique[END_REF]Mohamed-Abchir 1996). This deposit is thought to be emplaced during violent phreatic/phreatomagmatic events related to the flashing of an extensive hydrothermal system during the collapse of the Enclos Fouqué caldera [START_REF] Bachèlery | Le Piton de la Fournaise (Ile de la Réunion). Etude Volcanologique, Structurale et Pétrologique[END_REF]Mohamed-Abchir 1996;[START_REF] Fontaine | Constraints on hydrothermal processes on basaltic edifices: inferences on the conditions leading to hydrovolcanic eruptions at Piton de la Fournaise, Réunion Island, Indian Ocean[END_REF][START_REF] Upton | clasts in the, Piton de la Fournaise, Réunion Island, and their bearing on cumulative processes in the petrogenesis of the Réunion lavas[END_REF].

The ages of the caldera formation and related Bellecombe Ash unit are poorly constrained. They are likely comprised in a time span ranging between the emplacement of the lavas forming the uppermost part of the Enclos Fouqué walls that underly Bellecombe and Partage ashes (4745 ± 130 BP, 3340 ± 1012; respectively Er-39 and Er-41 in Table 8.1) and that of the crystal and lithic-rich Bellecombe and Partage ashes themselves (several ages between 4175 ± 145 and 2320 ± 90 BP; respectively Er-38, which matches the Bellecombe Ash type-section at the Petite Carrière outcrop, and Er-28 in Table 8.1). Interestingly, Vergniolle and Bachèlery (1982) report that ashes with an age of 2140 ± 80 BP (U3 of the "Partage Tephra" sequence, in this paper) drape the lower and inner wall of Bellecombe cliff. This possibly represents the upper age for a series of caldera-forming events.

Most of the eruptive products, lavas and tephras, cropping out inside the Enclos Fouqué caldera are much younger than 2320 BP, actually younger than 1750 CE (Table 8.1), final age of the widespread pāhoehoe lava field named CLEF by [START_REF] Lénat | Genèse du champ de lave de l'Enclos Fouqué: une éruption d'envergure exceptionnelle du Piton de la Fournaise (Réunion) au 18 ème siècle[END_REF]. Notable exceptions are the central cone and small scoria cones, like Formica Leo and Puy Mi-côte (Fig. 8.1), of unknown age, but covered by the CLEF pāhoehoe lava field.

Recent and detailed stratigraphic analysis of the 340 m high walls of the summit PdF caldera [START_REF] Roult | A new comprehensive classification of the Piton de la Fournaise activity spanning the 1985-2010 period. Search and analysis of short-term precursors from a broad-band seismological station[END_REF][START_REF] Michon | Explosive activity of the summit cone of Piton de la Fournaise volcano (La Réunion island): a historical and geological review[END_REF] failed in identifying deposits that could be related to major summit explosive events. [START_REF] Michon | Explosive activity of the summit cone of Piton de la Fournaise volcano (La Réunion island): a historical and geological review[END_REF] highlight that the summit cone evolution is mainly made by the alternation of crater collapse, lava infilling and outpouring episodes, suggesting a dominant effusive magmatic style punctuated by mild to weak explosive events unable to leave significant and durable traces on the territory. Moreover, the span of time covered by these processes is probably short [START_REF] Michon | Explosive activity of the summit cone of Piton de la Fournaise volcano (La Réunion island): a historical and geological review[END_REF]. For instance, caldera filling appears to be relatively rapid. The ca. 300 m-deep, 600 m-across 1931 summit collapse structure was filled in 2006, just before the major 2007 summit collapse event. This recent and dominantly effusive activity of PdF was preceded by an important strombolian to hawaiian activity, whose remnants is a basal cone made of red to ochre scoriae visible at the bottom of the present Dolomieu crater [START_REF] Michon | Explosive activity of the summit cone of Piton de la Fournaise volcano (La Réunion island): a historical and geological review[END_REF]. Both hawaiian, strombolian and possible phreatomagmatic deposit have been recognized in this lower sequence (Unit 1a and 1b in Peltier et al. 2012; U1a in [START_REF] Michon | Explosive activity of the summit cone of Piton de la Fournaise volcano (La Réunion island): a historical and geological review[END_REF]) at an elevation corresponding to the Enclos Fouqué caldera filling. The deposits related to this explosive phase of unknown age have not been identified outside the Enclos Fouqué [START_REF] Roult | A new comprehensive classification of the Piton de la Fournaise activity spanning the 1985-2010 period. Search and analysis of short-term precursors from a broad-band seismological station[END_REF][START_REF] Michon | Explosive activity of the summit cone of Piton de la Fournaise volcano (La Réunion island): a historical and geological review[END_REF].

Weak to mild explosive eruptions related to the central activity have left very little stratigraphic record, except near the summit cone [START_REF] Michon | Explosive activity of the summit cone of Piton de la Fournaise volcano (La Réunion island): a historical and geological review[END_REF]. For instance, fine ash and Pele's hairs of the 2007 caldera forming event have been quickly eroded away and only little traces are found inside the Bory crater, just 6 years after the event. The deposits of the most intense recent explosive eruptions (1961 and 1860) are only found near the volcano summit.

A notable exception is represented by the "Partage Tephra" sequence. Our new datings clearly indicate that the "Partage Tephra" sequence groups the deposits of several eruptions, which have occurred after a main event of breccia formation. These eruptions occurred in a relatively long period (-1124 to -52 BC; Table 8.1) and possibly represent an unusually violent series of events occurring soon after (and partially associated with) the last phase of Enclos Fouqué caldera collapse. These deposits give thus a lower limit for the age of the PdF central cone.

Along the N120°rift zone, the "Red Tephra" unit seems to pertain to a similar age interval. In this area, two 14 C ages (3735 ± 90 and 3205 ± 75 BP; respectively Er-37 and Er-35 in Table 8.1) are reported bracketing the underlying Bellecombe cpx-gabbro rich ash. Very similar ages (3715 ± 30 and 3220 ± 50 BP) were also found 1 km East from Piton dans le Bout (Er-37, Table 8.1) and in an ash bed underlying the Red Tephra near Commerson crater (Er-35, Table 8.1). The widespread presence in this sector, up to the Caldera des Sables rim (Er-30 to Er-36 in Table 8.1), of ash beds belonging to the "Bellecombe Ash unit" provide hence a upper limit for the age of the Red Tephra.

All tephra units identified in the period succeeding the "Partage" and "Red" tephra sequences have a very limited degree of dispersion. For instance, Er-21 and Er-20 new radiocarbon ages, respectively dated to 868 ± 30 and 620 ± 30 BP, identify two relatively recent and very localized events occurred close to Langevin area, inasmuch their deposits are absents both within the near Plaine des Sables (PDS2 core) and Pas des Sables (section S3; Fig. 8.4).

The most widespread lapilli bed of the Piton de la Fournaise's recent history is the "Black Tephra" unit, which marks the beginning of Chisny cone activity and is here dated for the first time at 381 ± 26 BP (Er-14 Table 8.1). It likely represents the most explosive magmatic event of a series of eccentric eruptions that have occurred along the three rift zones (NW, SE and NE) in a short and recent period (1400-1600 CE; Er-10 to Er-18 Table 8.1; [START_REF] Tanguy | Archeomagnetism of Piton de la Fournaise: bearing on volcanic activity at La Réunion Island and geomagnetic secular variation in Southern Indian Ocean[END_REF]). Interestingly, this series of closely spaced violent eruptions immediately preceded the first permanent human settlements on the island; consequently, without leaving any trace in the historical record.

Concluding Discussion

The characterization of the explosive activity and the research of violent paroxystic events over PdF massif has been performed through a drilling and excavation campaign supported by the integration of new radiocarbon ages to previous chronologic data. The use of a light shallow and continuous drilling system has proved to be a suitable methodology to execute surveys in an impervious territory, such in La Réunion, and to realize a detailed micro-stratigraphic study of the tephra emitted by the volcano over a relative recent period (last 5 kiloyear).

The stratigraphic study carried out on the cores confirms the presence of the "Bellecombe Ash unit" in a relatively superficial position, over a wide area ranging from the proximal area, near the Bellecombe caldera cliff and the Plaine des Sables, to at least the Plaine des Remparts, the middle-distal sector. The observation made at the microscopic scale does not allow us to extend this correlation to the most distal Grand Étang drill, located at 18 km from the PdF central cone, suggesting either the lacking of this deposit in the more distal areas or an age of the cones of Grand Étang younger than 3 kiloyear. Actually, the uncertainty about the age of the pyroclastic cones which close the Grand Etang lake basin (younger than 5730 ± 110 year BP; [START_REF] Banton | Rapport de thèse: Etude hydrogéologique d'un complexe alluvial en pays volcanique, sous climat tropical, site du Grand Étang-Ile de la Réunion[END_REF] does not permit to constrain its stratigraphic position with respect to -Bellecombe ashes. Occurrence of "Bellecombe" layers (<20 cm total thickness) on the Trous Blancs area ca. 13 km W-NW from the central cone suggest that this is the main dispersion axis of these ashes.

The review of the Bellecombe Ash unit shows that only few ash fallout beds attain the medial area, with a thickness quickly decreasing when moving away from the Enclos Fouqué caldera. These decimeter-thick beds correspond to the upper part of the type-section described by Mohamed-Abchir (1996) in proximal areas. The age interval (3735-3060 BP) of the upper beds results significantly younger than that of the lower beds (4880-4175 BP) and of the lava flow underlying the ashes near the rim of the Enclos Fouqué caldera (4745 BP) [START_REF] Bachèlery | Le Piton de la Fournaise (Ile de la Réunion). Etude Volcanologique, Structurale et Pétrologique[END_REF][START_REF] Staudacher | Ages of the second caldera of Piton de la Fournaise volcano (Réunion) determined by cosmic ray produced 3He and 21Ne[END_REF]. The "Partage Tephra" sequence, here described for the first time, can thus represent a sequence of events marking the end of the "Bellecombe ash unit" and puts an upper limit for the Enclos Fouqué caldera collapse events (2340 year BP for Unit 2). Therefore the Bellecombe Ash unit groups a sequence of eruptive events, which span a much wider time-period than previously thought. Anyhow, it represents the most traceable horizon (Fig. 8.5) among the studied deposits and no other pyroclastic blanket exhibits a similar regional dispersion in the last 5 kiloyear.

A second, more limited, correlation has been found in the drilling cores. It involves the "Black Tephra" lapilli bed drilled in the Plaine des Sables (PDS1 and PDS2, Fig. 8.5). The "Black Tephra" originates and is mainly distributed westward (Fig. 8.4) within the Plaine des Sables from possibly linear (fracture) source structure. The deposit dispersal exhibits a W elongation, in agreement with the Easterlies direction at Pas de Bellecombe (inset in Fig. 8.4, ground level records by Météo France). Such fact highlights that an eventual plume generated during the eruption was confined below the Trade winds inversion zone, at about 4 km a.s.l., and thus cannot exceeds the height of about 2 km inasmuch the tephra source is located at an altitude of 2300 m a.s.l. The Black Tephra maximum dispersal seems to vanish quickly, within about 3.7 km in the downwind direction and over an area of less than 13 km 2 . This deposit presents the typical features of the hawaiian activity. In particular it seems to be related to a lava fountaining generated through a fissural source. This activity results to be very young (381 ± 26 BP); calibrated ages (1447-1628 CE) suggest this unusual event occurred shortly before the beginning of permanent settlement on La Réunion island.

A fountaining activity of similar intensity to that of the Chisny event is possibly represented by the Red Tephra unit dispersed in the medial area. This deposit could be represented in the PLB core (Plaine des Remparts West) upper black lapilli sequence at least by the basal red ash-coated lapilli (Table 8.4) and in the PDE2 core (Plaine des Remparts East) by the reddish ash layer overlying the Bellecombe Ash unit (Table 8.3). However this correlation still remains a hypothesis to verify cause of the scarce characterization for the middle-distal sector deposits. The age of this event (younger than 3200 BP) and its stratigraphic position suggests that it occurred near the end of the Bellecombe ash unit emplacement.

Besides the Bellecombe Ash unit, the lack of regionally distributed lapilli blankets suggests that no violent strombolian or more intense eruptions (subplinian to plinian) have occurred in the recent story of the volcano's activity (<5 kiloyear). In particular, the distribution of the "Partage Tephra" sequence highlights that phreatomagmatic events can impact the proximal areas outside the Enclos Fouqué caldera, but with a limited extension. Moreover, the lack of a continuous lapilli/ash horizon from the proximal to distal areas points out that the lapilli cover that overlay the Plaine des Sables and the Plaine des Remparts is the result of several local blankets linked to several hawaiian to strombolian emission centers. As highlighted by new radiocarbon ages obtained on tephra lying on the Langevin Plateau and Plaine des Sables (respectively 868, 620 and 381 year BP in Table 8.1) this kind of activity persisted in the N120°rift up to very recent times and ended probably just before the island's colonization, leaving no trace in historical records. The eccentric activity persisted instead along the NE and SE rift zones but with a dominantly effusive style [START_REF] Michon | Explosive activity of the summit cone of Piton de la Fournaise volcano (La Réunion island): a historical and geological review[END_REF].

The maximum expected magmatic events have therefore to be related to intense hawaiian fountaining. The Black Tephra unit, emitted by a source area located near the Piton Chisny cone, represents a very recent and intense manifestation of this typology. The low amount of fine ashes and the NW elongation of its deposit, in fact, suggest the absence of the well-developed "cineritic" plume, which characterizes violent strombolian eruptions. Therefore, the implication for the risk assessment, and consequently for risk maps production and organization, must consider that lava fountaining, even if more vigorous than the normal, is the maximum magmatic explosive activity produced by Piton de la Fournaise in the last 5000 years. It implies that its dangerousness is restricted to a relatively brief distance from the source and that 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 eruptions on the inhabitants and the structures.

Fig. 8 . 1

 81 Fig. 8.1 Drilling locations (yellow dots) and dated eruptive events, inside stratigraphic sections, younger than 5000 year (green dots) on the NW rift. In the upper right corner: the Enclos Fouqué rim (light blue) and the three major rift zones (red areas) intersecting the PdF massif are shown. NW, SE and NE stand respectively for NW, SE and NE rift; R-B is the Ramond-Baril eruptive axis, corresponding to a N-S scoria cones alignment

Fig. 8

 8 Fig. 8.2 AF topcore 40 modified coring system and drilling operation. a The infission is performed by a jackhammer thrust, while b the extraction by a mechanical jack system. c Thin ash beds preserved in the PDS2 core

Fig. 8

 8 Fig. 8.3 "Partage Tephra" sequence. C1, C2, C3 fine ash (U1); C4 coarse ash (U2); C5 lapilli and ash, C6 well-sorted lapilli bed (U3); cc0, cc1, cc2 charcoal-rich layers (respectively dated to 2855, 2340 and 2140 year BP; Table8.1). Average grain size distribution for each Unit is plotted as histogram. The matrix-supported breccia underlying the "Partage Tephra" sequence is attributed to the "Bellecombe Unit"

Fig. 8

 8 Fig. 8.4 "Black Tephra" unit maximum dispersal. S3, S13 and S20 are the sites whose logs are shown in Fig. 7.5 . Wind strength and direction records at Pas de Bellecombe between 01/09/2007 and 15/03/2011 are reported in the down right corner (source Meteo France)

Fig. 8 . 5

 85 Fig. 8.5 Stratigraphic correlations from the distal to the proximal sector at NW of Piton de la Fournaise volcano. CdB Bellecombe Ashes; TN Black Tephra; TR? Red Tephra possible correlation; Rw reworked lapilli and ash

Table 8 .

 8 1 Dated eruptive event at Piton de La Fournaise volcano

	Eruption ID	Location	Unit name	Unit type	Note on the sample	Coordinates		Dating method	Age	±	Median	Calibrated	Calibrated
						x	y		(BP)		probability (A.D.)	min (A.D) 2σ	max (A.D.) 2σ
	Er-1	RZNE	1998 lava flow	Lava flow							1998	1998	1998
	Er-2	RZSE	1986 lava flow	Lava flow							1986	1986	1986
	Er-3	RZNE	1977 lava flow	Lava flow							1977	1977	1977
	REU140212-10/9	Central activity	Partage cliff	Ash beds	Historical eruptions;	366,212.7	7,653,718.8	14C	120		1831	1939	1679
					B layer; multiple
					fragments
	REU140212-S1-2b	Central activity	Partage cliff	Ash beds	Historical eruptions;	365,582.4	7,653,224.7	14C	130		1821	1941	1675
					B1 layer; top of
					historical sequence;
					single fragment
	Er-4	RZSE	1800 lava flow	Lava flow							1802	1802	1802
	Er-10	N120	Piton Rampe 14	Strombolian	Below the lava flow	363,034.827	7,654,507.466	14C	140		1791	nd	1528
				cone
	AND 02 / REU140721 / S1	N120	Trous Blancs area	Modern soil	Uppermost layer rich	355,338.72	7,655,654.69	14C	145		1801	1948	1668
					in roots and organic
					matter; multiple
					fragments
	REU031014-3	N120	Rivière des					14C	150		1785	1950 (nd)	1667
			Remparts
	Er-5	RZSE	1776 lava flow	Lava flow							1776	1776	1776
	Er-6	RZSE	1774 lava flow	Lava flow							1776	1774	1774
	REU140212-S4-2	Central activity	Partage cliff	Ash beds	Historical eruptions;	364,086.9	7,653,098.6	14C	160		1773	1950 (nd)	1664
					B layer; top of
					historical sequence;
					multiple fragments
	REU140521-BB1	RZNE	Piton Moka (near	Ash beds	In lapilli fall above the	376,943.4	7,656,622.4	14C	175		1770	1950 (nd)	1657
			Anses des		lahar reworking
			Cascades)		Bellecombe breccia;
					modern agricultural
					activity? multiple
					fragments
	AND 08 /	N120	Top of Trous	Modern soil		355,672.20	7,654,589.84	14C	195		1770	1950 (nd)	1648
	REU140728-2a / S1		Blancs site
	Er-7	RZSE	Puy Raymond	Strombolian	Inside ashes. 1 m	365,883.571	7,645,619.532	14C	45-115			nd	nd
				cone	below the lava flow
													(continued)

Table 8

 8

	.1 (continued)
	Eruption ID	Location	Unit name	Unit type	Note on the sample	Coordinates		Dating method	Age	±	Median	Calibrated	Calibrated
						x	y		(BP)		probability (A.D.)	min (A.D) 2σ	max (A.D.) 2σ
	Er-8	EF (lava above the	CLEF lava field	Lava field	Pahoehoe lava	364,160.653	7,652,535.955	Archeomagnetic			1750	ca. 1750
		Formica leo cone)
	Er-8	EF	CLEF lava field	Lava field	Pahoehoe lava			Historical			1740	1730	1750
								sources
	Er-9	RZNE	1708 lava flow	Lava flow							1708	1708	1708
	Er-8	EF (lava close to	CLEF lava field	Lava field	Sample RE-90-28;	364,160.653	7652535.955	Cosmogenic	250		1700	nd	nd
		Bellecombe steps)			pahohehoe
	REU140212-S1-2a	Central activity	Partage cliff	Ash beds	Historical eruptions;	365,582.4	7,653,224.7	14C	255		1650	1950 (nd)	1521
					B1 layer; top of
					historical sequence;
					multiple fragments
	Er-11	RZNE	Piton Nelson-	Strombolian	Near Bois Blanc	374,006.015	7,654,760.755	14C	260		1643	nd	1450
			Piton de Bois	cone	village
			Blancs
	REU140320-S5-4	Central activity	Partage cliff	Ash beds	Historical eruptions;	366,109.7	7,653,616.5	14C	340		1559	1639	1470
					multiple fragments
	Er-12	RZSE	Piton Taipoul	Strombolian	Below the scoriae of	366,430.576	7,645,458.601	14C	355		1549	1794	1427
				cone	the cone and above an
					ash bed
	Er-13	RZSE	Mare Longue lava	Lava flow	Below the lava flow			14C	364		1517	1632	1451
			flow
	Er-15	N120	Piton Chisny-lava	Polyphase	Near Chisny cone;			Archeomagnetic			1500	1600	1400
			with dunite	cone	phase 2 in Bachèlery
			enclaves near		1981
			Chisny cone
	Er-16	RZNE	Piton Indivis -Bois	Strombolian		376,033.1	7,655,634.376	14C	420		1500	1649	1327
			Blanc	cone
	Er-14	N120	Piton Chisny-	Multiple	Section 20; Plaine des	361,198.937	7,651,746.67	14C	381		1493	1630	1445
			Plaine des Sables	cones	Sables. near Piton
			black scoria fall		Chisny
	Er-17	RZSE	Ravine d'Ango	Strombolian	In conglomerate	374,511.652	7,638,425.555	14C	455		1457	1635	1318
			lava	cone	below the lava (the
					soil is not burned)
	Er-18	N120	Petit Cratère	Strombolian	Below the lava flow	361,293.907	7,655,150.227	14C	470		1443	1634	1305
				cone
	Er-19	RZSE	Le Baril 1 (Brulé	Strombolian	Basal scoriae below	365,841.284	7,638,409.566	14C	575		1358	1444	1281
			du Baril)	cone	the lava flow (Ravine
													(continued)

Table 8

 8

	.1 (continued)
	Eruption ID	Location	Unit name	Unit type	Note on the sample	Coordinates		Dating method	Age	±	Median	Calibrated	Calibrated
						x	y		(BP)		probability (A.D.)	min (A.D) 2σ	max (A.D.) 2σ
					Perote river) and
					above a soil
	Er-20	N120	Langevin plateau	Scoriae bed	Section 1-Caldera	360,176.998	7,650,157.619	14C	620		1349	1399	1292
			fall-bed 4		des Sables cliff
	Er-21	N120	Langevin plateau	Scoriae bed	Section 1-Caldera	360,176.998	7,650,157.619	14C	868		1177	1251	1046
			fall-bed 5		des Sables cliff
	Er-22	N120	"Piton Chisny	Lava flow	Below aa lava flow in	359,323.842	7,640,947.249	14C	1105		925	1022	775
			lavas" in Langevin		the Langevin valley
			valley
	Er-24	N120	Piton sous le Gite	Strombolian	Below the lava flow	363,211.109	7,653,672.45	14C	1465		578	675	420
				cone
	Er-23	Central activity?	Ashes on western	Ash beds		362,860.285	7,650,591.453	14C	1450		576	1122	50
			rim of Enclos
			Fouqué (near
			Chisny)
	Er-25	N120	Tephra on Les	Scoria bed	Sample REU	356,229.000	7,654,133.000	14C	1495		573	641	434
			Trous Blancs		1301-243 Trou Blanc
	Er-26	N120	Commerson crater	Scoria bed		359,258.678	7,654,094.665	14C	1890		119	249	-20
	Er-27	Central activity	Partage Tephra	Scoria bed	Section 6 (Partage	365,088.054	7,653,096.733	14C	2140		-179	-52	-356
			(Unit 3; CC2 layer)		cliff)
	Er-27	Central activity	Ashes on NW cliff	Ash bed	Ashes draping the	363495.684	7652284.643	14C	2140		-184	1	-381
			of Enclos Fouqué		lower third of the
			(Bellecombe cliff)		Enclos Fouqué cliff
	Er-28	Central activity	Ashes near the	Ash beds	Sampled near the	363,223.126	7,653,091.586	14C	2320		-403	-178	-755
			"Gite du Volcan"		Gites du Volcan
			("Cendres de
			Bellecombe" in
			B'81 and V&B'82)
	Er-28	Central activity	Partage Tephra	Ash bed	Section 6 (Partage	365,088.054	7,653,096.733	14C	2340		-402	-366	-506
			(Unit 2; CC1 layer)		cliff)
	Er-28	Central activity	Ashes near the	Ash beds	Upper part of an ash	365,412.448	7,653,098.027	14C	2390		-521	-235	-784
			"Gite du Volcan"		bed. below a bed of
					scoriae
	Er-28?	N120	Piton des Tangues	Lapilli bed?	Ash or lapilli bed			14C	2665		-841	608	-2345
			tephra (Below Red		above the Upper
			Tephra Unit)		Bellecombe ash
	Er-29	Central activity	Partage Tephra	Ash bed	Section 6 (Partage	365,088.054	7,653,096.733	14C	2855		-1021	-919	-1121
			(Unit1; CC0 layer)		cliff)
	REU140825-PDT2	N120	Near Piton des	Ash beds	Black soil below red	360,408.8	7,656,179.8	14C	2920		-1115	-1020	-1211
			Tangues parking		tephra lapillis
					covering Bellecombe
					falls
													(continued)

Table 8

 8

	.1 (continued)
	Eruption ID	Location	Unit name	Unit type	Note on the sample	Coordinates		Dating method	Age	±	Median	Calibrated	Calibrated
						x	y		(BP)		probability (A.D.)	min (A.D) 2σ	max (A.D.) 2σ
	Er-30	Central activity	Upper unit of	Ash bed	Sample REU 1303-07	359,775.000	7,654,645.000	14C	3060		-1326	-1228	-1411
			Bellecombe ash		A1
	Er-31	N120	Piton Sauvetage	Strombolian	Ash bed	361,424.89	7,655,382.022	14C	3085		-1335	-1127	-1501
				cone
	Er-32	Central activity	Upper unit of	Ash bed	Sample REU 1303-07	359,728.000	7,654,714.000	14C	3095		-1350	-1280	-1428
			Bellecombe ash		A2 2A
	Er-33	N120	Langevin plateau	Ash and	Section 1-Caldera	360,176.998	7,650,157.619	14C	3100		-1355	-1284	-1431
			fall-bed 6	lapilli bed	des Sables cliff
	Er-34	Central activity	Upper unit of	Ash bed	Sample REU 1303-07	359,728.000	7,654,714.000	14C	3110		-1377	-1288	-1437
			Bellecombe ash		A2 2C/1 km west of
					Piton des Basaltes
	Er-41	Central activity	Lava3 of W Enclos	Lava flow	Sample RE-90-15b	362,889.735	7,650,907.916	Cosmogenic	3340		-1390
			Fouqué rim		(below Bellecombe
					ash); oceanite
	REU140822-2	N120	0.5 km from Nez	Ash beds	Soil above	357,317	7,655,847	14C	3130		-1407	-1300	-1494
			de Boeuf. above		Bellecombe and
			Bellecombe ash fall		below a thin lapilli
					layer
	Er-41	Central activity	Lava3 of W Enclos	Lava flow	Sample RE-90-15a	362,889.735	7,650,907.916	Cosmogenic	3420		-1470
			Fouqué rim		(below Bellecombe
					ash); oceanite
	Er-35	N120	Piton des Tangues	Ash bed	Cpx-gabbro rich ash	360,442.092	7,656,281.636	14C	3205		-1483	-1288	-1656
			ashes ; Upper		bed (above Piton des
			Bellecombe ash		Tangues cone; Below
			(U3a)?		Red Tephra Unit)
	Er-35	N120	Ashes near	Ash bed	Fine ash bed near	359,258.678	7,654,094.665	14C	3220		-1495	-1411	-1615
			commerson (below		commerson
			red tephra unit)
	Er-42	Central activity	Lava2 of NW	Lava flow	Sample RE-90-31	363,890.37	7652624.595	Cosmogenic	3500		-1550
			Enclos Fouqué rim		(below partage unit)
	Er-36	N120	Piton des Basaltes	Strombolian	Scoriae bed	360,326.603	7,653,622.523	14C	3305		-1584	-1453	-1735
				cone
	Er-37	Central activity	Bellecombe ash;	Ash bed	Sample REU 1303-07	358,895.000	7,655,721.000	14C	3715		-2098	-2029	-2200
			upper bellecombe		A6/About 1 km east
			ash (U3a?)		of Piton dans l'bout
													(continued)

Table 8

 8

	.1 (continued)
	Eruption ID	Location	Unit name	Unit type	Note on the sample	Coordinates		Dating method	Age	±	Median	Calibrated	Calibrated
						x	y		(BP)		probability (A.D.)	min (A.D) 2σ	max (A.D.) 2σ
	Er-37	Central activity	Piton des Tangues	Ash beds	Cpx-gabbro rich ash	362,534.552	7,657,077.969	14C	3735		-2148	-1920	-2456
			ashes; upper		bed (above Piton des
			Bellecombe ash		Tangues lava; below
			(U3a)?		red Tephra unit)
	Er-43	Central activity	Lava1 of W Enclos	Lava flow	Sample RE-90-24a	362,798.548	7,650,082.1	Cosmogenic	4310		-2360
			Fouqué rim
	Er-43	Central activity	Lava1 of W Enclos	Lava flow	Sample RE-90-25	362,806.183	7,650,013.384	Cosmogenic	4550		-2600
			Fouqué rim
	AND 02/ REU140721/ S3b	N120	Trous Blanc site	Ash beds	Charcoals at the base	355,338.72	7,655,654.69	14C	4115		-2693	-2577	-2865
			(S3b ash below		of S3B yellow layer
			Bellecombe and		(unit just below
			above Trous Blanc		Bellecombe fall)
			eruption)
	Er-38	Central activity	Lower Bellecombe	Ash beds	Fossil wood	362,477.784	7,652,096.79	14C	4175		-2746	-2307	-3316
			ash Unit (U1b)		(unburned)
	AND 04/ REU140723-1/	N120	Piton Sec (S3b ash	Ash beds	Charcoals at the base	355,201.53	7,655,305.20	14C	4400		-3013	-2917	-3261
	S3b		below Bellecombe)		of S3B yellow layer
					(unit just below
					Bellecombe fall)
	AND 08/ REU140728-2a/	N120	Trous Blancs site;	Ash beds	Charcoals at the base	355,672.20	7,654,589.84	14C	4685		-3447	-3370	-3625
	bglaBR		top of the Trous		of L2(?) orange red
			Blancs Breccia		layer (unit just below
					Bellecombe fall)
	AND 12/ REU140801-2	N120	At the feet of Nez	Ash beds	Soi below thin lapilli;	356,562.22	7,654,352.30	14C	4695		-3454	-3370	-3629
			de Boeuf spatter		layer just below
			(below		Bellecombe fall
			Bellecombe)
	Er-39	Central activity	Lava2 of NW	Lava flow	Basal scoriae below	364,873.000	7,653,932.000	14C	4745		-3515	-3100	-3794
			Enclos Fouqué rim		the uppermost lava
					flow near Bellecombe
					(below Partage unit)
	Er-40	Central activity	Second unit of	Ash bed	Sample REU 1303-07	359,728.000	7,654,714.000	14C	4880		-3669	-3540	-3758
			Bellecombe ash		A2 2b/1 km west of
					Piton des Basaltes
	Er-43	Central activity	Lava1 of W Enclos	Lava flow	Sample RE-90-24b;	362,798.548	7,650,082.1	Cosmogenic	5130		-3180
			Fouqué rim		oceanite
	AND 02/	N120	Trous Blancs area	Ash beds	S3a ashes above the	355338.72	7655654.69	14C	5400		-4277	-4077	-4341
	REU140721/ S3a				Trous Blanc eruption
													(continued)

Table 8

 8

	.1 (continued)
	Eruption ID	Location	Unit name	Unit type	Note on the sample	Coordinates		Dating method	Age	±	Median	Calibrated	Calibrated
						x	y		(BP)		probability (A.D.)	min (A.D) 2σ	max (A.D.) 2σ
	REU140825-PDT1	N120	Piton des Tangues	Ash beds	Thick red lahar below	360,408.8	7,656,179.8	14C	5570		-4406	-4346	-4460
			parking		Bellecombe falls
	Er-44	Piton des Neiges?	Grand Etang deep	Conglomerate	Fossil wood	359,436.931	7,666,718.692	14C	5730		-4584	-4352	-4823
			drilling		(unburned) in
					conglomerates at the
					base of the Puy de
					l'Etang ashes
	Er-45	N120	"Les Trous Blancs"	Lava flow		356,050.106	7,654,462.838	Stratigraphic	6500
			lava field
	Er-46	N120	Ashes along the	Ash beds	Section 12; layer 5	360,408.937	7,656,181.043	14C	6965		-5847	-5745	-5975
			path to "Piton des		(above the "Cendres
			Tangues"		de Notre Dame" unit)
	Er-47	N120	Piton textor	Ash beds		358,199.373	7,656,293.751	14C	7125		-5999	-5740	-6231
	Er-48	N120	Ashes between	Ash beds		358,729.735	7,656,540.14	14C	7930		-6837	-6611	-7060
			Piton textor and
			Piton des Cailles
	AND 04/ REU140723-1/	N120	Trous Blancs area	Ash beds	S3a ash layer	355,201.53	7,655,305.20	14C	7985		-6915	-6709	-7051
	S3a		(near Piton sec;
			abobe Trous
			Blancs eruption)
	Er-49	N120	Piton dans le bout	Strombolian		358,474.994	7,655,901.2	14C	9355		-8658	-8254	-9223
				cone
	AND 06/ REU140723-3/	N120	Near Piton Sec	Ash beds		355,352.97	7,655,202.68	14C	9430		-8712	-8572	-8823
	S3b		(S3b ashes above
			the Trous Blanc
			eruption)
	Er-50	Piton des la	Grand Etang deep	Conglomerate	Fossil wood in	359,436.931	7,666,718.692	14C	10,650		-10,644	-10,238	-10,801
		Fournaise?	drilling		conglomerate below
					the deep lavas
					(-40 m) met by the
					drill
	REU031014-1BC	Piton des Neiges	Bras des Lianes					14C	12,040		-11,942	-11,802	-12,111
	Er-51	Central activity	Notre Dame de la	Ash beds		353,792.779	7,646,998.349	14C	15,200		-16,378	-12,873	-19,716
			Paix -2
	LAS 17/	N120	Bois Court lava	Lava flow		348,715.72	7,655,411.65	14C	17,780		-19,582	-19,222	-19,908
	REU140718-1/ Part B		flow
													(continued)

Table 8

 8

	.1 (continued)
	Eruption ID		Location	Unit name	Unit type	Note on the sample	Coordinates			Dating method	Age	±	Median	Calibrated	Calibrated
								x	y				(BP)		probability (A.D.)	min (A.D) 2σ	max (A.D.) 2σ
	LAS 17/ REU140718-1/	N120		Bois Court lava	Lava flow		348,715.72	7,655,411.65	14C		17,840	100	-19,664	-19,347	-19,948
	Part A				flow
	LAS 17/ REU140718-1/	N120		Bois Court lava	Lava flow		348,715.72	7,655,411.65	14C		17,970	100	-19,817	-19,507	-20,114
	Part C				flow
	Er-52		Central activity	"Cendres de Notre	Ash beds					Stratigraphic		19,000-
					Dame" Unit								37,000
	Er-53		N120		Bois court	Strombolian	Altered ash layer.	348,644.795	7,655,086.233	14C		19,185	265	-21,168	-20,540	-21,776
						cone	below the lava flow
	Er-54		Central activity	Plaine des Sables	Caldera fault	Sample RE-90-07;	360,074.551	7,650,976.811	Cosmogenic		23,800	2000	-21,850	-21,478	-30,115
					caldera fault		surface of the caldera
							fault
	Er-55		N120		Piton Manuel-	Strombolian		351,186.326	7,653,685.743	K/Ar		29,000		-27,050
					Piton des Cabris	cone
	Er-56		Central activity	Notre Dame de la	Ash beds		354,230.713	7,647,126.81	14C		37,200	1500	-39,467	-36,591	-42,016
					Paix -1
	Er-57		N120 SVZ	Piton Rouge (St.	Strombolian		356,019.22	7,638,466.955	K/Ar		57,000		-55,050
					Joseph)	cone
	Er-58		Central activity	Summit lava of the	Lava flow	Sample RE-90-06;	359,640.634	7,651,410.728	Cosmogenic		62,000	4000	-60,050
					Plaine des		last lavas of the
					Ramparts		caldeira
	Er-59		Central activity?	Submarine tephra	Ash bed	Sample R4-1; basaltic				18O		67,000	5000	-65,050
					(S17-656 drill)		ash
	Eruption ID	Location	Unit name	Unit type	Note on the sample	Calibrated probability		Calibrated probability	Calibrated probability	Reference
								distribution (A.D.)-Max	distribution (A.D.)	distribution (A.D.)-Tertiary
								probability 2σ		-Secondary probability 2σ	probability 2σ
								Min age	Max	%	Min age	Max	%	Min age	Max	%
									age	prob.		age	prob.			age	prob.
	Er-1	RZNE		1998 lava flow	Lava flow											Michon et al.
																(2013)
	Er-2	RZSE		1986 lava flow	Lava flow											Michon et al.
																(2013)
	Er-3	RZNE		1977 lava flow	Lava flow											Michon et al.
																(2013)
	REU140212-10/9	Central		Partage cliff	Ash beds	Historical eruptions; B layer;	1939	1801	65.9	1764	1679	34.1			This chapter
		activity				multiple fragments
	REU140212-S1-2b	Central		Partage cliff	Ash beds	Historical eruptions; B1 layer; top	1894	1799	44.4	1777	1675	39.9	1941		1905	15.7	This chapter
		activity				of historical sequence; single
						fragment
																(continued)

Table 8

 8

	.1 (continued)
	Eruption ID	Location	Unit name	Unit type	Note on the sample	Calibrated probability		Calibrated probability		Calibrated probability		Reference
						distribution (A.D.)-Max	distribution (A.D.)		distribution (A.D.)-Tertiary
						probability 2σ		-Secondary probability 2σ	probability 2σ
						Min age	Max	%	Min age	Max	%	Min age	Max	%
							age	prob.		age	prob.		age	prob.
	Er-4	RZSE	1800 lava flow	Lava flow											Michon et al.
															(2013)
	Er-10	N120	Piton Rampe 14	Strombolian	Below the lava flow										-
				cone
	AND 02 /	N120	Trous Blancs area	Modern soil	Uppermost layer rich in roots and	1890	1797	35	1781	1716	30.7	1711	1668	17.2	This chapter
	REU140721 / S1				organic matter; multiple fragments
	REU031014-3	N120	Rivière des Remparts			1783	1717	33.2	1889	1831	19.5	nd	1910	18.1	This chapter
	Er-5	RZSE	1776 lava flow	Lava flow											Michon et al.
															(2013)
	Er-6	RZSE	1774 lava flow	Lava flow											Michon et al.
															(2013)
	REU140212-S4-2	Central	Partage cliff	Ash beds	Historical eruptions; B layer; top of	1820	1719	50.1	nd	1913	18.4	1706	1664	17.8	This chapter
		activity			historical sequence; multiple
					fragments
	REU140521-BB1	RZNE	Piton Moka (near Anses	Ash beds	In lapilli fall above the lahar	1815	1725	55.6	1696	1657	19.4	nd	1917	18.7	This chapter
			des Cascades)		reworking Bellecombe breccia;
					modern agricultural activity?
					multiple fragments
	AND 08 /	N120	Top of Trous Blancs site	Modern soil		1811	1728	57.6	1691	1648	25.2	nd	1922	17.2	This chapter
	REU140728-2a /
	S1
	Er-7	RZSE	Puy Raymond	Strombolian	Inside ashes. 1 m below the lava										-
				cone	flow
	Er-8	EF (lava	CLEF lava field	Lava field	Pahoehoe lava										Tanguy et al.
		above the													(2011)
		Formica leo
		cone)
	Er-8	EF	CLEF lava field	Lava field	Pahoehoe lava										Michon et al.
															(2013)
	Er-9	RZNE	1708 lava flow	Lava flow											Michon et al.
															(2013)
	Er-8	EF (lava	CLEF lava field	Lava field	Sample RE-90-28; pahohehoe										-
		close to
		Bellecombe
		steps)
															(continued)

Table 8

 8

	.1 (continued)
	Eruption ID	Location	Unit name	Unit type	Note on the sample	Calibrated probability		Calibrated probability		Calibrated probability		Reference
						distribution (A.D.)-Max	distribution (A.D.)		distribution (A.D.)-Tertiary
						probability 2σ		-Secondary probability 2σ	probability 2σ
						Min age	Max	%	Min age	Max	%	Min age	Max	%
							age	prob.		age	prob.		age	prob.
	REU140212-S1-2a	Central	Partage cliff	Ash beds	Historical eruptions; B1 layer; top	1675	1621	59.1	1579	1521	21.3	1799	1777	16.4	This chapter
		activity			of historical sequence; multiple
					fragments
	Er-11	RZNE	Piton Nelson-Piton de	Strombolian	Near Bois Blanc village										Bachèlery
			Bois Blancs	cone											(1981)
	REU140320-S5-4	Central	Partage cliff	Ash beds	Historical eruptions; multiple	1639	1470	100							This chapter
		activity			fragments
	Er-12	RZSE	Piton Taipoul	Strombolian	Below the scoriae of the cone and										Tanguy et al.
				cone	above an ash bed										(2011)
	Er-13	RZSE	Mare Longue lava flow	Lava flow	Below the lava flow										Straberg (comm
															pers)
	Er-15	N120	Piton Chisny-lava with	Polyphase	Near Chisny cone; phase 2 in										Tanguy et al.
			dunite enclaves near	cone	Bachèlery (1981)										(2011)
			Chisny cone
	Er-16	RZNE	Piton Indivis-Bois Blanc	Strombolian											Bachèlery
				cone											(1981), map,
															Tanguy et al.
															(2011)
	Er-14	N120	Piton Chisny-Plaine des	Multiple	Section 20; Plaine des Sables. near										Di Muro et al.
			Sables black scoria fall	cones	Piton Chisny										(2012)
	Er-17	RZSE	Ravine d'Ango lava	Strombolian	In conglomerate below the lava (the										Tanguy et al.
				cone	soil is not burned)										(2011)
	Er-18	N120	Petit Cratère	Strombolian	Below the lava flow	1529	1384	69.8	1634	1544	17	1364	1305	13.2	Tanguy et al.
				cone											(2011)
	Er-19	RZSE	Le Baril 1 (Brulé du Baril)	Strombolian	Basal scoriae below the lava flow	1444	1281	100							Tanguy et al.
				cone	(Ravine Perote river) and above a										(2011)
					soil
	Er-20	N120	Langevin plateau fall-	Scoriae bed	Section 1-Caldera des Sables cliff	1399	1292	100							Di Muro et al.
			bed 4												(2012)
															(continued)

Table 8

 8

	.1 (continued)
	Eruption ID	Location	Unit name	Unit type	Note on the sample	Calibrated probability		Calibrated probability		Calibrated probability		Reference
						distribution (A.D.)-Max	distribution (A.D.)		distribution (A.D.)-Tertiary
						probability 2σ		-Secondary probability 2σ	probability 2σ
						Min age	Max	%	Min age	Max	%	Min age	Max	%
							age	prob.		age	prob.		age	prob.
	Er-21	N120	Langevin plateau fall-	Scoriae bed	Section 1-Caldera des Sables cliff	1251	1148	79.5	1090	1046	16.1	1139	112	4.4	Di Muro et al.
			bed 5												(2012)
	Er-22	N120	"Piton Chisny lavas" in	Lava flow	Below aa lava flow in the Langevin	1022	775	100							Albarède et al.
			Langevin valley		valley										(1997), pg. 174,
															Tanguy et al.
															(2011)
	Er-24	N120	Piton sous le Gite	Strombolian	Below the lava flow	675	420	100							-
				cone
	Er-23	Central	Ashes on western rim of	Ash beds		1047	50	98.9	1122	1088	0.7				Bachèlery
		activity?	Enclos Fouqué (near												(1981), pg. 137
			Chisny)
	Er-25	N120	Tephra on Les Trous	Scoria bed	Sample REU 1301-243 Trou Blanc	641	534	93.8	487	470	3.2	453	434	2.9	This chapter
			Blancs
	Er-26	N120	Commerson crater	Scoria bed		249	-1	99.5	-12	-20	0.5				Bachèlery
															(1981), Tanguy
															et al. (2011)
	Er-27	Central	Partage Tephra (Unit 3;	Scoria bed	Section 6 (Partage cliff)	-54	-231	78.2	-292	-354	21.8				Di Muro et al.
		activity	CC2 layer)												(2012)
	Er-27	Central	Ashes on NW cliff of	Ash bed	Ashes draping the lower third of the	1	-380	100							-
		activity	Enclos Fouqué		Enclos Fouqué cliff
			(Bellecombe cliff)
	Er-28	Central	Ashes near the "Gite du	Ash beds	Sampled near the Gites du Volcan	-178	-597	86	-680	-755	8.7	-607	-671	5.4	Bachèlery
		activity	Volcan" ("Cendres de												(1981)
			Bellecombe" in B'81 and
			V&B'82)
	Er-28	Central	Partage Tephra (Unit 2;	Ash bed	Section 6 (Partage cliff)	-366	-490	99.2	-501	-506	0.8				Di Muro et al.
		activity	CC1 layer)												(2012)
	Er-28	Central	Ashes near the "Gite du	Ash beds	Upper part of an ash bed. below a	-357	-784	97.5	-255	-283	1.9	-235	-246	0.6	-
		activity	Volcan"		bed of scoriae
	Er-28?	N120	Piton des Tangues tephra	Lapilli bed?	Ash or lapilli bed above the Upper	608	-2345	100							Abchir (1996),
			(Below Red Tephra Unit)		Bellecombe ash										pg. 86
	Er-29	Central	Partage Tephra (Unit1;	Ash bed	Section 6 (Partage cliff)	-919	-1121	100							Di Muro et al.
		activity	CC0 layer)												(2012)
															(continued)

Table 8

 8

	.1 (continued)
	Eruption ID	Location	Unit name	Unit type	Note on the sample	Calibrated probability		Calibrated probability		Calibrated probability		Reference
						distribution (A.D.)-Max	distribution (A.D.)		distribution (A.D.)-Tertiary
						probability 2σ		-Secondary probability 2σ	probability 2σ
						Min age	Max	%	Min age	Max	%	Min age	Max	%
							age	prob.		age	prob.		age	prob.
	Er-43	Central	Lava1 of W Enclos	Lava flow	Sample RE-90-25										-
		activity	Fouqué rim
	AND 02/	N120	Trous Blanc site (S3b ash	Ash beds	Charcoals at the base of S3B yellow	-2577	-2764	73.5	-2804	-2865	26.2	-2770	-2773	0.3	This chapter
	REU140721/ S3b		below Bellecombe and		layer (unit just below Bellecombe
			above Trous Blanc		fall)
			eruption)
	Er-38	Central	Lower Bellecombe ash	Ash beds	Fossil wood (unburned)	-2336	-3110	97.9	-3237	-3266	0.8	-3293	-3316	0.6	Abchir (1996),
		activity	Unit (U1b)												pg. 86
	AND 04/	N120	Piton Sec (S3b ash below	Ash beds	Charcoals at the base of S3B yellow	-2917	-3098	99.1	-3254	-3261	0.9				This chapter
	REU140723-1/		Bellecombe)		layer (unit just below Bellecombe
	S3b				fall)
	AND 08/	N120	Trous Blancs site; top of	Ash beds	Charcoals at the base of L2(?)	-3370	-3477	68.9	-3482	-3525	23.7	-3600	-3625	7.4	This chapter
	REU140728-2a/		the Trous Blancs Breccia		orange red layer (unit just below
	bglaBR				Bellecombe fall)
	AND 12/	N120	At the feet of Nez de Boeuf	Ash beds	Soi below thin lapilli; layer just	-3370	-3476	60.7	-3483	-3532	23.4	-3582	-3629	15.9	This chapter
	REU140801-2		spatter (below		below Bellecombe fall
			Bellecombe)
	Er-39	Central	Lava2 of NW Enclos	Lava flow	Basal scoriae below the uppermost	-3263	-3794	92.3	-3100	-3246	7.7				Bachèlery
		activity	Fouqué rim		lava flow near Bellecombe (below										(1981)
					Partage unit)
	Er-40	Central	Second unit of Bellecombe	Ash bed	Sample REU 1303-07 A2 2b/1 km	-3634	-3713	97.2	-3540	-3556	1.6	-3743	-3758	1.3	This chapter
		activity	ash		west of Piton des Basaltes
	Er-43	Central	Lava1 of W Enclos	Lava flow	Sample RE-90-24b; oceanite										-
		activity	Fouqué rim
	AND 02/	N120	Trous Blancs area	Ash beds	S3a ashes above the Trous Blanc	-4227	-4341	89.5	-4167	-4202	7.8	-4077	-4095	2	This chapter
	REU140721/ S3a				eruption
	REU140825-PDT1	N120	Piton des Tangues parking	Ash beds	Thick red lahar below Bellecombe	-4346	-4460	100							This chapter
					falls
	Er-44	Piton des	Grand Etang deep drilling	Conglomerate	Fossil wood (unburned) in	-4352	-4800	99.7	-4819	-4823	0.3				Banton (1985)
		Neiges?			conglomerates at the base of the
					Puy de l'Etang ashes

Table 8

 8

	.1 (continued)
	Eruption ID	Location	Unit name	Unit type	Note on the sample	Calibrated probability		Calibrated probability		Calibrated probability		Reference
						distribution (A.D.)-Max	distribution (A.D.)		distribution (A.D.)-Tertiary
						probability 2σ		-Secondary probability 2σ	probability 2σ
						Min age	Max	%	Min age	Max	%	Min age	Max	%
							age	prob.		age	prob.		age	prob.
	Er-45	N120	"Les Trous Blancs" lava	Lava flow											Villeneuve and
			field												Bachèlery
															(2006)
	Er-46	N120	Ashes along the path to	Ash beds	Section 12; layer 5 (above the	-5745	-5918	93.4	-5950	-5975	6.6				Di Muro et al.
			"Piton des Tangues"		"Cendres de Notre Dame" unit)										(2012)
	Er-47	N120	Piton textor	Ash beds		-5740	-6231	100							Bachèlery
															(1981)
	Er-48	N120	Ashes between Piton	Ash beds		-6611	-7060	100							Bachèlery
			textor and Piton des												(1981)
			Cailles
	AND 04/	N120	Trous Blancs area (near	Ash beds	S3a ash layer	-6752	-7051	98.7	-6709	-6720	1.3				This chapter
	REU140723-1/		Piton sec; abobe Trous
	S3a		Blancs eruption)
	Er-49	N120	Piton dans le bout	Strombolian		-8254	-9223	100							Bachèlery
				cone											(1981)
	AND 06/	N120	near Piton Sec (S3b ashes	Ash beds		-8597	-8823	99.2	-8572	-8565	0.8				This chapter
	REU140723-3/		above the Trous Blanc
	S3b		eruption)
	Er-50	Piton des la	Grand Etang deep drilling	Conglomerate	Fossil wood in conglomerate below	-10,427	-10,801	96.2	-10,287	-10,339	2	-10,350	-10,396	1.5	Banton (1985)
		Fournaise?			the deep lavas (-40 m) met by the
					drill
	REU031014-1BC	Piton des	Bras des Lianes			-11,802	-12,111	100							This chapter
		Neiges
	Er-51	Central	Notre Dame de la Paix -2	Ash beds		-12,873	-19,716	100							-
		activity
	LAS 17/	N120	Bois Court lava flow	Lava flow		-19,222	-19,908	100							This chapter
	REU140718-1/
	Part B
	LAS 17/	N120	Bois Court lava flow	Lava flow		-19,347	-19,948	100							This chapter
	REU140718-1/
	Part A
															(continued)

Table 8

 8

	.1 (continued)
	Eruption ID	Location	Unit name	Unit type	Note on the sample	Calibrated probability		Calibrated probability	Calibrated probability	Reference
						distribution (A.D.)-Max	distribution (A.D.)	distribution (A.D.)-Tertiary
						probability 2σ		-Secondary probability 2σ	probability 2σ
						Min age	Max	%	Min age	Max	%	Min age	Max	%
							age	prob.		age	prob.	age	prob.
	LAS 17/	N120	Bois Court lava flow	Lava flow		-19,507	-20,114	100		This chapter
	REU140718-1/
	Part C
	Er-52	Central	"Cendres de Notre Dame"	Ash beds
		activity	Unit
	Er-53	N120	Bois court	Strombolian	Altered ash layer. below the lava	-20,540	-21,776	100		-
				cone	flow
	Er-54	Central	Plaine des Sables caldera	Caldera fault	Sample RE-90-07; surface of the					-
		activity	fault		caldera fault
	Er-55	N120	Piton Manuel-Piton des	Strombolian						-
			Cabris	cone
	Er-56	Central	Notre Dame de la Paix -1	Ash beds		-36,591	-42,016	100		-
		activity
	Er-57	N120 SVZ	Piton Rouge (St. Joseph)	Strombolian						-
				cone
	Er-58	Central	Summit lava of the Plaine	Lava flow	Sample RE-90-06; last lavas of the					-
		activity	des Ramparts		caldeira
	Er-59	Central	Submarine tephra	Ash bed	Sample R4-1; basaltic ash					Fretzdorff et al.
		activity?	(S17-656 drill)							(2000)

Abbreviation: EF Enclos Fouqué; CLEF Enclos Fouqué Lava Field; RZSE SE rift zone; RZNE NE rift zone; N120 NW rift zone

Table 8 .

 8 2 GDE core description and coarse ash (710 < φ < 1000 μm) optic microscope analysis

	106-168
	168-176
	176-179
	179-200
	200-207
	207-214
	214-347
	347-350
	350-362
	362-371
	371-378
	378-381
	381-397
	397-409
	409-623

Legend Stratigraphic log: G gravel; GS gravel and sand; S sand; C Clay; R coherent rock. Microscopic analysis: ol olivine; pl plagioclase; px pyroxene; qz quartz; mt magnetite; v glass; μxx microcrystalline; xx crystals; ag fine sand aggregates; lth lithics/lava fragments (as part of μxx). Quantities: x abundant/frequent; x some; x few; tr trace Table

8

.3 PDE2core description and coarse ash (710 < φ < 1000 μm) optic microscope analysis Legend Stratigraphic log: G gravel; GS gravel and sand; S sand; C Clay; R coherent rock. Microscopic analysis: ol olivine; pl plagioclase; px pyroxene; qz quartz; mt magnetite; v glass; μxx microcrystalline; xx crystals; ag fine sand aggregates; lth lithics/lava fragments (as part of μxx). Quantities: x abundant/frequent; x some; x few; tr trace Table

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.4 PLB core description and coarse ash (710 < φ < 1000 μm) optic microscope analysis Legend Stratigraphic log: G gravel; GS gravel and sand; S sand; C Clay; R coherent rock. Microscopic analysis: ol olivine; pl plagioclase; px pyroxene; qz quartz; mt magnetite; v glass; μxx microcrystalline; xx crystals; ag fine sand aggregates; lth lithics/lava fragments (as part of μxx). Quantities: x abundant/frequent; x some; x few; tr trace Table

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.5 PDS2 core description and coarse ash (710 < φ < 1000 μm) optic microscope analysis Legend Stratigraphic log: G gravel; GS gravel and sand; S sand; C Clay; R coherent rock. Microscopic analysis: ol olivine; pl plagioclase; px pyroxene; qz quartz; mt magnetite; v glass; μxx microcrystalline; xx crystals; ag fine sand aggregates; lth lithics/lava fragments (as part of μxx). Quantities: x abundant/frequent; x some; x few; tr trace Table

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.6 PDS1 core description and coarse ash (710 < φ < 1000 μm) optic microscope analysis Legend Stratigraphic log: G gravel; GS gravel and sand; S sand; C = Clay; R coherent rock. Microscopic analysis: ol olivine; pl plagioclase; px pyroxene; qz quartz; mt magnetite; v glass; μxx microcrystalline; xx crystals; ag fine sand aggregates; lth lithics/lava fragments (as part of μxx). Quantities: x abundant/frequent; x some; x few; tr trace

Acknowledgments The Préfecture, Protection Civile and DEAL of the La Réunion and the MEEDDAT (Ministère de l'Ecologie, du Développement Durable et de l'Energie) are acknowledged for promoting, supporting and partially financing this project on volcanic hazard assessment at Piton de la Fournaise (convention n°11_037 and 1321; 2011-2014). A. Morandi was supported by a grant of the Department of Earth Sciences of the University of Florence (entitled to prof. Orlando Vaselli).


Claudia Principe

Andrea Morandi

Andrea Di Muro

Laurent Michon

Laurent Michon Volcanological

Patrick Bachelery

Jean-François Lenat

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

niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Volcanological Map of the Plaine des Sables, Piton de la Fournaise Claudia Principe, Andrea Morandi, Andrea Di Muro and Laurent Michon

The "Plaine des Sables" (PdS) is the main entry door for the visitor approaching the summit area of Piton de la Fournaise (PdF) basaltic shield volcano. The plain, located between 2300 and 2400 m asl and 5 km west of PdF summit crater, owes its name to a m-thick continuous cover of basaltic lapilli that strongly contrast with the dominantly effusive behavior of PdF. Several cones of variable volume and size and related lava flows occur scattered inside the PdS.

This map is the first detailed map of PdS and represents a first attempt to introduce synthematic units for the study of the Piton de la Fournaise volcanological district. The new cartography is offered in this first version with a relatively detailed resolution (1:5000) and on a DEM base (courtesy of N. Villeneuve, OVPF). Synthematic mapping is based on unconformity surfaces, which permit to define key geological events inside the stratigraphic succession of volcanic deposits [START_REF] Salvador | Unconformity-bounded stratigraphic units[END_REF]). In the PdS case, this approach allowed grouping the whole PdS activity occurred after the collapse of the "Plaine des Sable" caldera (Plaine des Sables Synthem; <60-24 ka; [START_REF] Merle | Calderas, landslides and paleo-canyons on Piton de la Fournaise volcano (La Réunion island, Indian Ocean)[END_REF][START_REF] Staudacher | Ages of the second caldera of Piton de la Fournaise volcano (Réunion) determined by cosmic ray produced 3 He and 21 Ne[END_REF] by means of a first order unconformity represented by the collapse scarp itself. The eastern side of the PdS is bounded by a second scarp related to the younger (<4.8 ka) "Enclos Fouqué" caldera [START_REF] Bachèlery | Le Piton de la Fournaise (Ile de la Reunion). Etude volcanologique, structurale et petrologique du Piton de la Fournaise, Ile de La Reunion -Volcanological, structural and petrological study of Piton de la Fournaise, La Réunion island[END_REF]Ort et al. 2015). Inside the PdS Synthem, the stratigraphic unit of Bellecombe ashes (#bac) groups at least three eruptive events occurred between 4880 ± 35 BP and 2855 ± 35 BP [START_REF] Morandi | Pre-historic explosive activity at Piton de la Fournaise volcano[END_REF]Ort et al. 2015) and represents the main depositional marker over the whole PdS area. Bellecombe ashes were emplaced during the main explosive (phreatomagmatic) event known at PdF [START_REF] Bachèlery | Le Piton de la Fournaise (Ile de la Reunion). Etude volcanologique, structurale et petrologique du Piton de la Fournaise, Ile de La Reunion -Volcanological, structural and petrological study of Piton de la Fournaise, La Réunion island[END_REF][START_REF] Michon | Explosive activity of the summit cone of Piton de la Fournaise volcano (La Réunion island): a historical and geological review[END_REF][START_REF] Morandi | Pre-historic explosive activity at Piton de la Fournaise volcano[END_REF]) and whose source area was partly located inside the PdS itself (Ort et al. 2015). Several cones (e.g. #c) and voluminous lava units (#ol and #oc) predate Bellecombe activity. The age of #oc lavas emitted before Enclos Fouqué collapse by central vents located east of the PdS is in the range 5.1-3.5 ka [START_REF] Staudacher | Ages of the second caldera of Piton de la Fournaise volcano (Réunion) determined by cosmic ray produced 3 He and 21 Ne[END_REF] aphyric to olivine-rich (oceanite) basalts and span the whole range of surface textures known at PdF (Morandi et al. 2015). An outstanding feature of many lavas cropping out in the PdS is the abundance of ultramaphic (dunite-werhlite) nodules, testifying unusually deep magmatic storage levels [START_REF] Bureau | Magma-conduit interaction at Piton de la Fournaise volcano (Réunion island): a melt and fluid inclusion study[END_REF].

Two main lapilli units (Chisny Black Tephra, #bt and Haüy Yellow Tephra #h2) permit stratigraphic correlation across most of the PdS area. Beside typical monogenetic activity widespread on PdF massif, at least three large polygenetic centers can be identified inside PdS: Demi Piton, Piton Chisny, and Piton Haüy [START_REF] Michon | Rift zones and magma plumbing system of Piton de la Fournaise: how do they differ from Hawaii and Etna?[END_REF]Morandi et al. 2015[START_REF] Morandi | Pre-historic explosive activity at Piton de la Fournaise volcano[END_REF]. Their eruptive dynamics ranges from violent lava fountaining (e.g. #bt and #h2) to long lasting effusive behavior (e.g. 'Gueule Rouge' lava lake, east of Chisny Rampart; #gr3). With the notable exception of Bellecombe ashes, phreatomagmatic activity seems to play only a very minor role in the activity of the PdS. Bellecombe ashes have been grouped in a single sub-synthem, which permits to propose a relative chronology for the largest cones of the PdS, namely Demi Piton #dp (pre-Bellecombe), Haüy #h and Chisny cones #cy and #pcy (post-Bellecombe). The main age constraints for the youngest part of the volcanic sequence correspond to a radiocarbon age of 1105 ± 60 BP for a lava down the Langevin valley (Bachelery 1981;[START_REF] Tanguy | Archeomagnetism of Piton de la Fournaise: bearing on volcanic activity at La Réunion Island and geomagnetic secular variation in Southern Indian Ocean[END_REF]) and an even younger age for the Black Tephra fall emplaced during the late activity of Chisny cone (381 ± 26 BP; [START_REF] Morandi | Pre-historic explosive activity at Piton de la Fournaise volcano[END_REF]. Mapping of Piton Chisny and Piton Haüy products highlights the presence of two Debris Avalanches deposits (DAD #cy1 and #h3b) and related scarps and hummocks, as well as the morphological evidence of a number of eruptive and non-eruptive fractures.

The unvegetated lapilli cover which gives the name to the Plaine des Sables was mainly originated from the young activity of lava fountaining of Chisny (southern part of the plain) and Haüy (northern part of the plain) eruptive centers. In the central and northern portion of the map, other minor lapilli blankets are present, but have very limited dispersion, confined close to the source areas [START_REF] Morandi | Pre-historic explosive activity at Piton de la Fournaise volcano[END_REF].

Our work demonstrates that the Plaine des Sables has been the site of frequent and sometimes violent eruptive activity even in recent times, shortly before the beginning of human settlement on the La Réunion island. This excentric activity of PdF was periodically able to shed ashes and lapillis all over and outside the Plain des Sables. The most voluminous eruptions emitted lavas able to propagate down the main valleys, towards the villages and the towns located at the feet of the PdF massif. Most important, this excentric activity does not correspond only to monotonous piling of lavas or mild strombolian activity from a single constant source. PdS activity indeed developed on scattered and sometimes long-living eruptive centers and was able to produce a wide span of eruptive behaviors and volcanic hazards. The Plaine des Sables must therefore be considered as one of the most active and potentially hazardous sectors of the PdF massif [START_REF] Muro | Evaluation de l'aléa volcanique a La Réunion[END_REF]2015).

  Fig. S1Supplementary figure: Volcanological map of Plain des Sables, Piton de la Fournaise (Ile de la Réunion, France)