20 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 (Salvador 1987). 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; Merle et al. 2010; Staudacher and Allègre 1993) by means of a first order unconformity represented by the collapse scarp itself. The east- ern side of the PdS is bounded by a second scarp related to the younger (<4.8 ka) “Enclos Fouqué” caldera (Bachèlery 1981; Ort et al. 2015). Inside the PdS Synthem, the stratigraphic unit of Belle- combe ashes (#bac) groups at least three eruptive events occurred between 4880 ± 35 BP and 2855 ± 35 BP (Morandi et al. 2016; Ort et al. 2015) and represents the main depositional marker over the whole PdS area. Bellecombe ashes were emplaced during the main explosive (phreato- magmatic) event known at PdF (Bachèlery 1981; Michon et al. 2013; Morandi et al. 2016) 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 (Staudacher and Allègre 1993). Lavas range from Electronic supplementary material The online version of this chapter (doi:10.1007/978-3-642-31395- 0_20) contains supplementary material, which is available to authorized users. C. Principe (&) Á A. Di Muro Istituto di Geoscienze e Georisorse, CNR Pisa, Italy e-mail: c.principe@igg.cnr.it A. Morandi Dipartimento di Scienze della Terra, University of Florence, Florence, Italy A. Di Muro Observatoire Volcanologique du Piton de la Fournaise (OVPF), IPGP, Bourg Murat, France L. Michon Laboratoire GéoSciences, Université de La Réunion and IPGP, Saint Denis, France © Springer-Verlag Berlin Heidelberg 2016 P. Bachèlery et al. (eds.), Active Volcanoes of the Southwest Indian Ocean, Active Volcanoes of the World, DOI 10.1007/978-3-642-31395-0_20 327