Modern and historical tropical cyclone and tsunami deposits at the coast of Myanmar: Implications for their identification and preservation in the geological record
Modern and historical tropical cyclone and tsunami deposits at the coast of Myanmar: Implications for their identification and preservation in the geological record
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DOI：
10.1111/sed.12586
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发表时间：
2020-04-01
期刊：
影响因子：
3.5
通讯作者：
Brueckner, Helmut
中科院分区：
文献类型：
--
作者：
Brill, Dominik;Seeger, Katharina;Brueckner, Helmut
2008年5月热带气旋"纳尔吉斯"造成的灾难性风暴潮表明缅甸面临沿海洪灾。对热带气旋"纳尔吉斯"及其前身留下的沉积物的调查是对该区域今后热带气旋和海啸影响的准备工作的一个重要贡献，因为这可能会扩大长期灾害评估数据库，使之超越相对较短的仪器记录和历史记录。这项研究首次展示了缅甸沿海现代和历史热带气旋和海啸的沉积物。其目的是确定区域沉积特征，以帮助识别和区分地质记录中的气旋和海啸，并记录沉积后最初几年热带风化造成的沉积后变化。这些发现，如果用来解释更老的存款将延长现有的仪器记录的洪水事件在缅甸。对可能与2006年热带气旋马拉和2004年印度洋海啸等特定事件有关的沉积物进行评估，发现这两类沉积物具有相似的沉积特征。向陆地变薄和变细趋势、沿岸的沉积物来源和急剧的下部接触使得可以区分下伏沉积物，而根据所应用的方法，区分热带气旋和海啸起源是具有挑战性的。现代的类似物也表明，由于碳酸盐溶解，有机表层土壤的形成和海岸侵蚀，砂层的保存潜力相当低。然而，在海岸洼地，在海岸线弯曲或稳定的地方，可能会保存足够厚度（> 10 cm）的砂层。在若开邦海岸海滩山脊平原最向海的洼地，除了2006年热带气旋马拉的沉积物外，还发现了两个沙层。根据光释光、放射性碳和Cs-137测年的组合，较年轻的砂层与1982年的热带气旋Gwa有关，而较老的砂层很可能是1950年之前发生的事件的结果。与历史记录的比较表明，档案只对直接在研究区域或以北约几十公里处登陆的4级（或更高）热带气旋敏感。虽然所呈现的热带气旋记录仅限于过去100年，但海滩脊的光激发光年龄表明，本研究中所研究的海滩脊向陆地的洼地可能提供至少过去700年的热带气旋信息。
The catastrophic storm surge of tropical cyclone Nargis in May 2008 demonstrated Myanmar's exposure to coastal flooding. The investigation of sediments left by tropical cyclone Nargis and its predecessors is an important contribution to prepare for the impact of future tropical cyclones and tsunamis in the region, because they may extend the database for long-term hazard assessment beyond the relatively short instrumental and historical record. This study, for the first time, presents deposits of modern and historical tropical cyclones and tsunamis from the coast of Myanmar. The aim is to establish regional sedimentary characteristics that may help to identify and discriminate cyclones and tsunamis in the geological record, and to document post-depositional changes due to tropical weathering in the first years after deposition. These findings if used to interpret older deposits will extend the existing instrumental record of flooding events in Myanmar. Evaluating deposits that can be related to specific events, such as the 2006 tropical cyclone Mala and the 2004 Indian Ocean tsunami, indicates similar sedimentary characteristics for both types of sediments. Landward thinning and fining trends, littoral sediment sources and sharp lower contacts allow for the differentiation from underlying deposits, while discrimination between tropical cyclone and tsunami origin is challenging based on the applied methods. The modern analogues also demonstrate a rather low preservation potential of the sand sheets due to carbonate dissolution, formation of organic top soils, and coastal erosion. However, in coastal depressions sand sheets of sufficient thickness (>10 cm) may be preserved where the shoreline is prograding or stable. In the most seaward swale of a beach-ridge plain at the Rakhine coast, two sand sheets have been identified in addition to the deposits of 2006 tropical cyclone Mala. Based on a combination of optically stimulated luminescence, radiocarbon and Cs-137 dating, the younger sand layer is related to 1982 tropical cyclone Gwa, while the older sand layer is most probably the result of an event that took place prior to 1950. Comparison with historical records indicates that the archive is only sensitive to tropical cyclones of category 4 (or higher) with landfall directly in or a few tens of kilometres north of the study area. While the presented tropical cyclone records are restricted to the last 100 years, optically stimulated luminescence ages of the beach ridges indicate that the swales landward of the one investigated in this study might provide tropical cyclone information for at least the past 700 years.