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Geomorphology of Rodrigues Island, Indian Ocean: implications for the Réunion hotspot

Loraine Gourbe t1, Vincent Famin2,5, Julien Seghi2,5, Ghozy el Fatih3, Daniel O'Hara1, Sean F. Gallen4, Eric Gayer5, Laurent Michon2,5

  • Affiliations: 1GFZ Helmholtz Center for Geosciences, Potsdam, Germany; 2Université de La Réunion, Laboratoire Géosciences Réunion, Saint Denis, France; 3Faculty of Georesources and Materials Engineering, RWTH Aachen University, Aachen, Germany; 4Department of Geosciences, Colorado State University, Fort Collins, USA; 5Université Paris Cité, Institut de Physique du Globe de Paris, Paris, France

  • Presentation type: Poster

  • Presentation time: Tuesday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 174

  • Programme No: 3.5.33

  • Theme 3 > Session 5

Abstract

Rodrigues Island (110 km2, maximum elevation of 398 m) is the third youngest island related to the Réunion hotspot. Based on DEM analysis and observations from field campaigns performed in 2022 and 2024, we aim to i) infer the chronology of the island formation from its morphology, ii) reconstruct the general shape of the island prior to erosion, in order to estimate lava emission rates, and iii) constrain the landscape response time to volcanic activity. In western Rodrigues, a drowned valley, the presence of volcanic islets, and a sinuous coast line suggest an older landscape. This is consistent with recent radiometric dating and field surveys indicating that the island formed in at least two steps, the western part being the older one. Buttes capped by lava flows and paleo-valley refilling correspond to remnants of younger volcanic activity that covered western Rodrigues and formed the central and eastern portions of the island. Valleys in central and eastern Rodrigues form a simple radial drainage network with knickpoints distributed between 100 and 250 m of elevation. Most knickpoints show a rough positive power-function trend with catchment area and distance to river outlet. These knickpoints are likely related to post-eruption regressive erosion, with average horizontal propagation rates of ~1-2 mm/yr. To reconstruct the shape of the younger volcanic edifice, we use two DEM-based geometrical methods that use uneroded surfaces, such as relict portions of the original volcano flanks. We will discuss our results and their implications on the intensity of the Réunion hotspot activity.