Browsing by Author "Strotz, L"

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    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.
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    Expanding the proxy toolkit to help identify past events: Lessons from the 2004 Indian Ocean Tsunami and the 2009 South Pacific Tsunami
    (Elsevier, 2011-07-01) Chagué-Goff, C; Schneider, JL; Goff, JR; Dominey-Howes, D; Strotz, L
    Some of the proxies used to identify palaeotsunamis are reviewed in light of new findings following the 2004 Indian Ocean Tsunami and the 2009 South Pacific Tsunami, and a revised toolkit provided. The new application of anisotropy of magnetic susceptibility (AMS) to the study of tsunami deposits and its usefulness to determine the hydrodynamic conditions during the emplacement of tsunami sequences, together with data from grain size analysis, are presented. The value of chemical proxies as indicators of saltwater inundation, associated marine shell and/or coral, high-energy depositional environment, and possible contamination, is demonstrated and issues of preservation addressed. We also provide new findings from detailed studies of heavy minerals. New information gathered during the UNESCO - International Oceanographic Commission (IOC) International Tsunami Survey of fine onshore sediments following the 2009 South Pacific Tsunami is presented, and includes grain size, chemical, diatom and foraminifera data. The tsunami deposit varied, ranging from fining-upward sand layers to thin sand layers overlain by a thick layer of organic debris and/or a mud cap. Grain size characteristics, chemical data and microfossil assemblages provide evidence for marine inundation from near shore, and changes in flow dynamics during the tsunami. (C) 2011 Elsevier B.V.
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    Predecessors to the 2009 South Pacific tsunami in the Wallis and Futuna archipelago
    (Elsevier Science, 2011-07-01) Goff, JR; Lamarche, G; Pelletier, B; Chagué-Goff, C; Strotz, L
    Multi-proxy studies of trench sediments from Futuna island, in the Wallis and Futuna archipelago, have produced a record of two palaeotsunamis dated to around 1860-2000 BP and c. 470 BP. One of the most useful proxies in this study has been the archaeological data associated with occupations that immediately underlie the deposits associated with both palaeotsunamis. The reworking of the archaeological material into the palaeotsunami deposits and the additional chronological control provided by artefacts have added value to interpretations based upon more conventional earth science proxies. The identification of tsunamigenic sources for these events is tentative and based upon known potential sources. Based upon a comparison between the effects of the 2009 South Pacific tsunami and those recorded in the trenches, Event 1(1860-2000 BP) appears most likely to be associated with a large tsunami sourced from the Tonga-Kermadec Trench region. There are only rare contemporaneous events reported from around the region, although this appears to be largely due to a lack of similar research as opposed to a lack of evidence. Event 2 (c. 470 BP) is markedly larger than Event 1, with sedimentary evidence indicating significant inland inundation and runup around the entire island. There are several lines of evidence for a contemporaneous event in the South Pacific around 470 BP, although much of this needs further verification. Determining a source for this event is problematic because it must take in to account the regional signal and the significant impacts recorded on Futuna. We propose that the source for this younger event was either a larger Tonga-Kermadec Trench-related earthquake or the Kuwae caldera collapse in 1452/1453 AD. We recognise that as further research is carried out in the Pacific we will greatly improve our abilities to identify past sources and the magnitude and frequency of past events from these areas. This can only serve to improve our understanding of the regional risk from tsunamis. (C) 2010 Elsevier B.V. All rights reserved.
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    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.