Project Report

My EAPSI work focused on coastal hazards in Vietnam, which borders the western South China Sea (Figure 1). My research group analyzed sediment cores from An Cu Lagoon near Da Nang, Vietnam that was affected by large typhoons in 2006 and 2009. We conducted grain size analysis on sediment samples taken from the lagoon in order to identify and characterize overwash storm deposits that were preserved in the sediment record. By characterizing the modern storm deposits, we hope to be able to identify similar storm events deeper in the geologic record. This will allow us to reconstruct the long-term record of storms along the Da Nang coastline. The ability to identify past storms in the sediment record is instrumental to assessing hazards on a coastline that may not have a complete written history of large and destructive storm events. Results from preliminary analysis conducted during the EAPSI summer program show evidence of three higher-energy, coarser-grained deposits in core 3, and two coarser-grained and shelly high-energy deposits in core 4. It is interesting to note that the two cores seem to preserve overwash events differently, with core 3 containing evidence of three distinctive grain size populations while a layer of highly fragmented shells and massive in situ shells dominates the lithology of core 4. The distinctive sediment layers found in each core suggests that different parts of the lagoon may record high-energy storm events in different ways. Future analysis will focus on running treated grain size samples, dating the lagoon sediments, and conducting microfossil analysis. Treating the sediment samples with hydrochloric acid will remove the shells from the sediment and produce more accurate grain size results. In addition, the identification of species and a calculation of the percent of fractured shells will help determine the provenance of the sediment and the magnitude of the high-energy event that deposited the shells in the lagoon. One of the most important aspects of the overwash deposit study is the accurate dating of the lagoon sediments; without a chronology of sediment deposition, the typhoon deposits cannot be related to historical marine inundations with certainty. Future work will focus on the dating of the lagoon sediments from the activity-depth profile of excess 210Pb and 137Cs, naturally occurring radionuclides that are introduced to the lagoon from the atmosphere. Dating the sediments will determine whether the coarser grained and shelly deposits represent the 2006 and 2009 typhoons that are known to have affected the area. Finally, microfossil analysis will help determine the provenance of the overwash deposits. The main focus of the microfossil work will be to identify marine microfossils that were introduced into the brackish lagoon by the storm overwash. An investigation of modern microfossil assemblages in the lagoon sediment and offshore marine sediment will provide baseline information on what microfossils we would expect to find within the lagoon and what microfossils would be indicative of a marine incursion. The research we have conducted in An Cu lagoon is the first of its kind in Vietnam and addresses the need to better understand the potential impact of large storms on coastal populations. Although large storms repeatedly devastate coastal areas, studies focused on understanding the frequency and magnitude of storms are rare. In addition, very few studies have investigated the microfossil assemblages within coastal lagoons and in offshore sediments in Vietnam. We have addressed this problem by investigating the characteristics of overwash deposits produced by modern typhoons and relating the modern deposits to overwash deposits found deeper in the sediment record. In this manner, we can begin to reconstruct a history of storm events along this coastline and better assess coastal hazards in the An Cu region. Characterizing storm overwash deposits in Vietnam will open the door for similar work in the region as the viability of the methodology is realized.

National Science Foundation (NSF)
Office of International and Integrative Activities (IIA)
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Carter Kimsey
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Dura Cristina
United States
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