Browsing by Author "Etienne, S"

Now showing 1 - 4 of 4
  • No Thumbnail Available
    Item
    Deposits, flow characteristics, and landscape change resulting from the September 2009 South Pacific Tsunami in the Samoan Islands
    (Elsevier Science, 2011-07-01) Richmond, B; Buckley, M; Etienne, S; Chagué-Goff, C; Clark, K; Goff, JR; Dominey-Howes, D; Strotz, L
    The September 29th 2009 tsunami caused widespread coastal modification within the islands of Samoa and northern Tonga in the South Pacific. Preliminary measurements indicate maximum runup values of around 17 m (Okal et al., 2010) and shore-normal inundation distances of up to similar to 620 m (Jaffe et al., 2010). Geological field reconnaissance studies were conducted as part of an UNESCO-IOC International Tsunami Survey Team survey within three weeks of the event in order to document the erosion, transport, and deposition of sediment by the tsunami. Data collected included: a) general morphology and geological characteristics of the coast, b) evidence of tsunami flow (inundation, flow depth and direction, wave height and runup), c) surficial and subsurface sediment samples including deposit thickness and extent, d) topographic mapping, and e) boulder size and location measurements. Four main types of sedimentary deposits were identified: a) gravel fields consisting mostly of isolated cobbles and boulders, b) sand sheets from a few to similar to 25 cm thick, c) piles of organic (mostly vegetation) and man-made material forming debris ramparts, and d) surface mud deposits that settled from suspension from standing water in the tsunami aftermath. Tsunami deposits within the reef system were not widespread, however, surficial changes to the reefs were observed. Published by Elsevier B.V.
  • Thumbnail Image
    Item
    A palaeorainfall record from Central Pacific over the last millennia from speleothems: preliminary results
    (International Union For Quaternary Research (INQUA), 2014-07-07) Couchoud, I; Drysdale, RN; Hellstrom, JC; Hua, Q; Spötl, C; Etienne, S
    The South Pacific Convergence Zone (SPCZ) is a major feature of the South Pacific basin. Its position and activity fluctuate seasonally and at interannual and decadal timescales under the influence of ENSO and the IPO, driving changes in temperature and precipitation in the region. Zonal SPCZ events have also been shown to be associated to cyclogenesis in the Central Pacific, inducing serious hazards for the islands and populations of French Polynesia1. The reconstruction of past SPCZ position and intensity for pre-industrial periods could help to understand its dynamics and improve models aimed at predicting its evolution in a context of global change but long-term, highly resolved and chronologically well-constrained archives of palaeoclimate from the tropical South and Central Pacific are scarce. To address this issue, we collected speleothems from caves located on the uplifted atoll of Rurutu, in the Australes archipelago at the eastern part of the SPCZ. We present preliminary speleothem proxy data of regional palaeohydrology covering the last few millennia.
  • Thumbnail Image
    Item
    Reconstruction des paléoprécipitations sur les îles Australes (Pacifique central) au cours des derniers millénaires à partir de spéléothèmes : résultats préliminaires
    (Société Géologique de France (SGF), 2015-10-13) Couchoud, I; Drysdale, RN; Hellstrom, JC; Hua, Q; Spötl, C; Etienne, S
    La Zone de Convergence du Pacifique Sud (SPCZ) est une caractéristique majeure du bassin Pacifique Sud. Sa position et son intensité fluctuent de manière saisonnière et à des échelles interannuelles et décennales sous l’influence d’ENSO et de l’IPO, conduisant à des changements de température et de précipitations dans la région. L’association entre orientation zonale de la SPCZ et cyclogenèse dans le Pacifique central a été démontrée et induit de sérieux aléas pour les îles et populations de Polynésie française. La reconstruction des positions et intensités passées de la SPCZ pour la période pré-industrielle pourrait aider à comprendre sa dynamique et améliorer les modèles visant à prévoir son évolution dans un contexte de changement climatique global. Toutefois les archives climatiques de la zone tropicale du Pacifique Sud et du Pacifique central sont rares. Pour contribuer à combler cette lacune, nous avons collecté des spéléothèmes provenant de deux grottes localisées sur l’atoll soulevé de Rurutu, dans l’archipel des Australes (Polynésie française), dans la partie orientale de la SPCZ. Les spéléothèmes sont capables d’enregistrer les changements hydrologiques dans leur calcite sous forme de variations des rapports isotopiques de l’oxygène, de concentration en certains éléments traces ou encore de fines couches d’argiles déposées lors d’ennoiements. Nous présentons ici des résultats préliminaires d’analyse de ces proxies, interprétés en termes de paléohydrologie. Leurs enregistrements couvrent les derniers millénaires et sont calés chronologiquement par une combinaison de datations uranium-thorium et radiocarbone.
  • No Thumbnail Available
    Item
    The use of boulders for characterising past tsunamis: lessons from 2004 Indian Ocean and 2009 South Pacific tsunamis
    (Elsevier, 2011-07-01) Etienne, S; Buckley, M; Paris, R; Nandasena, AK; Clark, K; Strotz, L; Chagué-Goff, C; Goff, JR; Richmond, B
    Tsunamis are high energy events capable of transporting extremely heavy loads including boulders. We compare boulder deposits created by two modern tsunami events, the 2004 Indian Ocean and the 2009 South Pacific tsunamis, where the boulder sources were in similar topographic settings, and for which we have accurate data on the wave characteristics. Boulder distribution, preferential orientation and numerical simulation of boulder transport are discussed. A comparison between the impacts of the South Pacific and Indian Ocean tsunamis shows similar characteristics, such as limited landward extent and the absence of landward fining. Differences between the results from modelling and field data are most probably caused by variables such as coastal plain roughness (buildings, trees), microtopography, particle shape, and boulder collision during transport that are summarised as coefficients in the mathematical models. Characterising modern events through coarse sediment deposits provides valuable information to help identify and interpret palaeo-tsunami imprints on coastal landscapes. (C) 2011 Elsevier B.V.