2008 POST-TSUNAMI FIELD SURVEY REPORT

Transcription

1 2008 POST-TSUNAMI FIELD SURVEY REPORT FIELD SURVEY ON ASSESSMENT OF TSUNAMI LONGTERM EFFECTS AND PILOT PALEOTSUNAMI SURVEY NIRAN CHAIMANEE, WITOLD SZCZUCIŃSKI, PASSKORN KUNTHASAP, WISUT CHOTIKASATHIEN Bangkok, 15th February 2008

2 1. Introduction and objectives This report presents initial results of the field survey conducted three years after the December 2004 tsunami in the coastal zone of the Andaman Sea coast of Thailand (Fig. 1). The survey was a part of cooperation between Department of Mineral Resources of the Kingdom of Thailand and Adam Mickiewicz University in Poznań, Poland, initiated after the 2004 tsunami with the technical assistance of CCOP Geo-Environment Manager. The tsunami caused also changes in coastal ecosystems. One of its indicators are meiofauna communities, which in general showed fast recovery after the tsunami (Kotwicki & Szczuciński 2006). We repeating collected samples from the same locations as in the previous years to monitor any changes and distinguish tsunami caused impacts from long-term trends. Another good environmental indicator is phytoplankton. It was collected in ponds, which were flooded by tsunami waves. Phytoplankton analysis should provide information about algae flora changes in such ponds which were flooded by tsunami waves. Algae flora composition should provide information if any brackish or marine species can still occur in these ponds after two years after tsunami events or if typical freshwater species could adapted to such a drastically change conditions. Tsunami often leaves a layer of sediments that may be preserved in the geologic record. The geologic record may then be used to help assess tsunami hazard. In some cases, this record may be the only evidence that a region may be at risk from a tsunami. Where more than one tsunami deposit is preserved in a stratigraphic sequence, the record may help determine how often a tsunami is likely to occur. Since the tsunami from the December 2004 was the first wave of such a dimension in this region during the human written history it is important to document any earlier events. However, characteristic and preservation potential of tsunami sediments vary from one place to another due to differences in climatic conditions, vegetation cover and morphology. So, one of our objectives was to visit the same locations as in the previous field surveys to document if and in which way the tsunami sediments were altered. Chemical analysis has been carried on to monitor the impact of salt and heavy metal elements contamination discovered since 2004 tsunami. 2

3 Fig.1. The field studies (A, B) along the Andaman Sea of Thailand: several transects from Ao Klong Rion (south of Khao Lak), Laem Pakarang, Bang Sak I and II, Bang Mor, Nham Kem to northern tip of Kho Khao and Phra Thong islands (C) and Tri Trang Beach, Patong and Kamala on Phuket Island (D). 3

4 Paleotsunami sediments are potentially preserved in lake, lagoon or marsh areas. Since they have been reported in Phra Thong Island, we wished to examine if they are any signs of them in other environments. We did several excavations to investigate the sediments of the coastal plain on that island. The main objectives of the fieldwork were: - to collect samples of tsunami deposits and soil from the same locations as before to study the changes in biogeochemistry after the next rainy season; - to collect samples of plants to find out if elevated contents of bioavailable toxic elements in tsunami deposits are transferred and bioaccumulated in plants; - to sample beach environment for meiofauna assemblages to monitor their evolution after the tsunami; - to revisit the same locations as in previous surveys and to document tsunami deposits preservation potential; - to look for paleotsunami record; - to collect diatom samples from modern environments to obtain a reference for using them as a proxy in studies of the last tsunami deposits as well as potential paleotsunami; - to observe landscape changes after the tsunami. Fig.2. The coastal vegetation from northern Khao Lak area fully recovered from the 2004 tsunami. 2. Methods 4

5 At each site all the conditions were noted, taking in account both natural and anthropogenic factors. Detail photo documentation was made as well. In cases of boulder deposits all the major boulders were measured, Samples of tsunami deposits, underlying sediments, modern beach deposits and associated layers were collected from pits up to 1.5 m deep (Fig.4). They were collected in most cases at the same locations as during the previous survey. The geographical coordinates were obtained with GPS. Every time, the sample was averaged and approximately 150 g was taken to the polyethylene bags. Samples collected for chemical analysis were affected by UV irradiation (field lamp with antibacterial fluorescent light Philips) in order to limit biological activity and stabilize a composition of the sample. Fig.3. Trench (over 1.3 m deep) in tsunami impacted area in Phra Thong Island. Plant samples were collected from sites digging out whole plants together with roots and than rinsed with freshwater to remove any air deposits. Next collected plants were dried and transported to laboratory for further analysis Water samples were collected by phytoplankton net for plankton samples (Fig.4), benthic and peryphitic samples were collected using tooth brush. Several stones were usually brushed or submerged plants were squeezed to removed from them attached diatoms. All samples were preserved using Lugol s solution and formaldehyde. Water samples for phytoplankton analysis were collected from surface layer of water column. One liter of water was collected from both sites which enable than to conduct quantitative analysis and note the most abundant species. 5

6 Fig.4. Taking samples of plankton with phytoplankton net. 3. Work report The fieldwork started on the 2nd of February and lasted until the 08th of February The activities were concentrated along a stretch of Andaman Sea coast between Phuket island and northern tip of Kho Khao Island (Phuket and Phang Nga province) (Fig.1). Daily report on the undertaken activities: sampling of tsunami deposits, soils and beach meiofauna communities, observations of tsunami deposits preservation potential on Tri Trang beach and Patong beach (Patong Bay, Phuket Island); Ao Klong Rian observations on tsunami transported boulders (also possible paleotsunami), sampling of tsunami sediments and soils in Bang Sak I and II; sampling of beach meiofauna communities, search for paleotsunami on southern Phra Thong Island; observations of tsunami deposits preservation potential on Laem Pakarang; search for paleotsunami in Bang Sak II; sampling of tsunami deposits and soils, observations of tsunami deposits preservation potential in Bang Mor and Nham Kem; search for paleotsunami in Bang Mor; sampling of beach meiofauna communities, observations of tsunami deposits preservation potential along transects on northern and central Kho Khao island; search for paleotsunami on central Kho Khao; transfer to Bangkok; 6

7 4. Preliminary results and intended analytical work Chemical investigations of the tsunami deposits and soil after rainy season include processes of Samples preparation for the analyses, Determination of the sample s mobile components, Macroelements determination, Heavy metals determination, Speciation analysis and Determination of the elements composition During our survey most of the locations investigated during the previous investigations were visited In general, except places where man-made changes took place or where the tsunami sediment layer was very thin (less than 1 cm) the sedimentary record of the last tsunami is moderately preserved. Usually the uppermost portion (about 1-5 cm) was altered, due to growing plants (e.g. Figs. 5). However, at the locations where some sedimentary structures were preserved within the tsunami sediments (e.g. in Khor Khao) clearly show the different of grain-size and depositional environment (e.g. Figs. 6). These findings are very important in context of paleotsunami studies and suggest possibility of preservation tsunami sediment layer in coastal zone within sequence of coastal plain sands. Fig.5. Bioturbation is the main factor of deterioration of tsunami upper layer. 7

8 Fig.6. mud ball was eroded from lagoonal clay layer (in dark gray color) and mix within tsunami sand layer above. The possibility of finding record of paleotsunami in coastal zone of Thailand was reported in Phra Thong Island. However, this survey did not discover the said record yet. They are not typical settings for preservation tsunami record in sediments. Paleotsunami sediments are usually preserved in lake, lagoon or marsh deposits. We made attempts to find them in lagoonal sediments behind the beach ridge. Due to limited of time, the detail and through survey along the beach barrier on Phra Thong Island will be planned for next year survey. 5. Conclusions The most important preliminary findings of the field survey are: - tsunami sediment layer was moderately preserved after three rainy season (with more than 3000 mm of rainfall) and its preservation potential may be degraded than expected before; -The vegetation in the coastal zone has completely recovered, except some trees; -the nearshore (beach) zone is slightly prograding in some areas and regarding in some parts of the coastline as stable; 6. Acknowledgements We would like to express our deep acknowledgements to many persons and organizations that gave us valuable help and support during the work. We are indebted to Mr.Apichai Chvacharernpun - The Director General of the Department of Mineral Resources of Kingdom of Thailand and Dr. Sommai Techawan Chief of Foreign Affairs section of DMR for initiation of the research and help in logistical part. We thank Professor Stanisław Lorenc Rector of Adam Mickiewicz University in Poznań. Poland,Royal Thai Government and CCOP have been acknowledged for supporting and co-financing of the survey. We appreciate to Professor Bogdan Góralczyk Ambassador of Poland in Thailand and Mr. Krzysztof Dobrowolski for very valuable 8

9 support in organization of the research. We appreciate help of our field assistances: Mr. Therapong and Mr. Prasert Lekngam from DMR. 7. References Kotwicki, L. & Szczuciński, W., 2006: Meiofauna assemblages and sediment characteristic of sandy beaches on the west coast of Thailand after the 2004 tsunami event. Phuket Marine Biological Centre Research Bulletin 67: