The tsunami and cyclone hazard in Myanmar - Surveying coastal geoarchives for sedimentary evidence of extreme wave events
Final Report Abstract
During a field survey in Myanmar, deposits of modern and historical tropical cyclones and the 2004 Indian Ocean tsunami (IOT) were identified in various sediment archives at the Rakhine and Tanintharyi coast. Modern analogues such as 2006 TC Mala or the 2004 IOT, for which a correlation between sediment and the respective event is unambiguous, have been used to characterise the local storm and tsunami deposits with regard to sediment composition (grain size, fauna, geochemistry), sedimentary structure and spatial extent. Both types of event deposits show similar characteristics, including sharp lower contacts to the underlying substrate, landward fining and thinning trends, marine fauna from various water depths, high carbonate contents and low concentrations of organic carbon, as well as high values in the marine elements Ca and Sr. While the similarity of sedimentary tsunami and storm properties makes their discrimination challenging, the observation that weak tsunamis generate similar sediments as strong tropical cyclones is an important aspect to the general debate on discrimination criteria between both types of events. In a second step, these local criteria have been used to identify the imprints of tropical cyclones and tsunamis in the geological record. Although the preservation potential under the tropical conditions of the study area is generally low, older tropical cyclone deposits have been identified in the swales of beach-ridge plains at the Rakhine coast. These sand sheets can be correlated with historical tropical cyclones in 1982 (TC Gwa) and the 1950s using a combination of radiocarbon, luminescence and radiocaesium dating, approaches which have been evaluated with regard to dating accuracy using modern analogues. Comparison with the complete historical record indicates that the swales of the beach-ridge plains only archive local tropical cyclones of category 4 or stronger, while less intense cyclones did not leave imprints in the geological record. Thus, sediments stored in the swales can be used to improve the regional long-term hazard assessment by studying older swales of the beach-ridge plain for potential event deposits. Luminescence ages for the formation of some of the ridges indicate that the entire beach-ridge complex has the potential to further extend the regional tropical cyclone record to at least the last 700 years.
Publications
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2019. Modern and historical tropical cyclone and tsunami deposits at the coast of Myanmar: implications for their identification and preservation in the geological record. Sedimentology
Brill, D., Seeger, K., Pint, A., Reize, F., Kay Thwe Hlaing, Seeliger, M., Opitz, S., Khin Mi Mi Win, Win Thuzar Nyunt, Nilar Aye, Aung Aung, Kyaw Kyaw, Kraas, F., Brückner, H.
