Geomorphic evolution of the Piton des Neiges volcano (Réunion Island, Indian Ocean): Competition between volcanic construction and erosion since 1.4 Ma Tiffany Salvany a, b , Pierre Lahitte a, ⁎, Pierre Nativel, Pierre-Yves Gillot a a IDES UMR-CNRS 8148, Univ. Paris-Sud, Equipe géochronologie et évolution des systèmes volcaniques, Orsay, F-91405, France b LPGNantes UMR-CNRS 6112, Laboratoire Géosciences, Univ. du Maine, 72085 Le Mans Cedex 9, France abstract article info Article history: Received 2 April 2010 Received in revised form 3 June 2011 Accepted 10 June 2011 Available online 12 July 2011 Keywords: Réunion Island K–Ar dating Geomorphology Erosion Relief inversion Surface modeling Réunion Island (Indian Ocean) is a volcanic complex whose eruptive history was dominated by the activity of two main edifices: Piton des Neiges (PN) and Piton de la Fournaise (PF) volcanoes. The tropical climate induces erosion processes that permanently compete with volcanic constructional processes. Exposed to the trade winds and associated heavy rainfalls, the northeastern part of the island exhibits the most complex morphological evolution. Geomorphological analysis, performed on a 50 m DEM and associated to new K–Ar ages has clarified the overall history of PN volcano. Each massif is assigned to one of the main building stages of the edifice. In addition, the arrangement of these different massifs reveals that the eruptive phases have led to successive relief inversions and successive excavations of large central depressions in the proximal area. As a result, the younger massifs are always located in more proximal parts of the volcano, the youngest being close to the edifice center. In distal areas, early lava flows were channeled into valleys incised along the massif boundaries, leading to a more complex geochronological organization. Quantitative study of the dissection of PN volcano allows us to propose a minimum eroded volume of 101 ± 44 and 105 ± 41 km 3 for the Mafate and Cilaos “Cirques” (depressions), respectively, during the last 180 kyr and a minimum average long-term erosion rate of 1.2 ± 0.4 km 3 /ka. This leads us to estimate the removed volume during the whole history of PN volcano (N 1000 km 3 ) as equivalent to the volume of the deposits identified on the submarine flanks of Piton des Neiges volcano. Therefore, as regressive erosion appears to be the prevailing geomorphic process during the whole PN history, it questions the presence of major flank collapses younger than 1.4 Ma on this volcano. Erosion processes have largely been neglected in recent models, but our study emphasizes them as a key component of landscape development and a major process in the morphological evolution of Réunion Island that has to be fully integrated in future studies. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Growth and destruction of volcanoes result from the complex and close interplay of endogenous and exogenous processes, i.e. from both constructive and destructive phases acting near simulta- neously (Thouret, 1999). Growth rates of shield volcanoes are relatively high (0.02 km 3 /yr; e.g., Moore and Clague, 1992), and as a consequence many of these volcanoes are prone to massive flank collapses or slope failures resulting from structural instability. If such catastrophic events are common in the long-term evolution of volcanic oceanic islands, such as Hawaii and the Canary archipelagos (Moore et al., 1989; Mitchell et al., 2002) and Tahiti Island (Hildenbrand et al., 2004), they represent an infrequent natural hazard. In contrast, smaller and shallow landslides are the usual expression of erosion processes, especially on high-relief volcanoes subjected to heavy rainfalls during cyclonic events in tropical climates (e.g., Garcin et al., 2005). Volcanic geomorphology studies allow discriminating between the respective contributions of these processes in order to reconstruct the volcanic landform history and unravel the succession of building and destruction stages. The comprehension of processes involved in the morphostructural evolution is also essential to establish the past eruptive history. Furthermore, when combined with radiometric ages, geomorpho- metrical studies help to establish the complete eruptive history of the volcanic edifice. In the last decade, remote studies have been greatly simplified by the use of Digital Elevation Models (DEM). In addition to qualitative studies, DEM analysis allows quantitative geomorphology investiga- tions, such as the calculation of built and eroded volumes in order to infer the building and erosion rates. Such studies have been successfully applied to tropical volcanic islands such as Tahiti in the Pacific Ocean (Hildenbrand et al., 2008), Guadeloupe Island, (Lesser Antilles; Samper et al., 2007; Lahitte et al., this issue) or Martinique Island (Lesser Antilles, Germa et al., 2010). Geomorphology 136 (2012) 132–147 ⁎ Corresponding author. Tel.: + 33 1 69156773; fax: + 33 1 69154891. E-mail address: pierre.lahitte@u-psud.fr (P. Lahitte). 0169-555X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.geomorph.2011.06.009 Contents lists available at ScienceDirect Geomorphology journal homepage: www.elsevier.com/locate/geomorph