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Our study presents the results of determining labile aluminium form in samples from the 2004 tsunamiaffected coastal zone of Thailand. The samples were collected from tsunami deposits, beach sediments, sediments underlying the tsunami deposits (pre 2004 tsunami soil), as well as from soils from areas, that were not flooded. The extraction of the labile form of aluminium was performed using 3 mol L⁻¹ HCl in twelve grain size fractions. In the surface layer samples the highest concentrations were determined in the tsunami deposits in fractions <0.063 mm (5850 mg kg⁻¹). The highest determined concentration in the whole set of investigated samples occurred in soil sample in fractions 0.09-0.125 mm (19770 mg kg⁻¹). An increase in concentration of labile aluminium form, along with decreasing grain diameter, was observed in samples from all the studied settings. In general, concentrations were higher in soil samples not affected by the tsunami. This is probably due to steady weathering of minerals during soil forming processes and removal of sediment grain surface coatings potentially enriched in labile Al during high energy transport by tsunami.
Heavy mineral assemblages were studied in onshore sandy deposits from the 26 December 2004 tsunami on Kho Khao Island, southern Thailand. The most common minerals included tourmalines, zircon, muscovite, biotite, limonites and opaque minerals. An abundance of micas and depletion in tourmalines allowed us to distinguish the tsunami deposits from modern beach sediments and pre-tsunami soils. Major lateral and vertical changes in the studied profiles were related to an increase in flake-shaped micas upward in the tsunami sequence as well as landward. These variations, although documented for one grain size fraction, corresponded well with changes in the grain size distributions of the whole samples. The observed changes probably reflect wave hydrodynamics and a change in the sedimentation mode from bed-load deposition to settling of the suspended load.
Tsunami deposits are often characterized by specific diatom assemblages, which may indicate sediment provenance and help identify paleotsunami deposits. In the present study diatom assemblages were studied in tsunami deposits left by the 2004 tsunami in Thailand, as well as in beach sediments, inner shelf marine sediments and freshwater ponds and streams. The assemblages in tsunami deposits had chaotic structure and consisted of species found in all the studied habitats, suggesting erosion of terrestrial and marine sediments by tsunami. The diatom frustules in tsunami deposits were generally rare and often damaged due to excessive wave force. The most common identified species were Amphora turgida Gregory, Cocconeis scutellum Ehrenberg, Diplomenora cocconeiformis (Schmidt) Blazé, Eunotogramma marinum (W. Smith) Peragallo (typical for benthos of marine and brackish environments), and taxa common in freshwaters, including Cyclotella ocellata Pantocsek, Cocconeis placentula Ehrenberg and Encyonema silesiacum (Bleish) D.G. Mann.
On December 26th, 2004, a tsunami hit the Andaman Sea coast of Thailand, leaving bimodal tsunami deposits in the coastal zone. Granite boulders and sandy tsunami deposits were investigated near Thap Lamu Navy Base in Phang Nga Province, Thailand. Boulders (< 2.5m³) were mostly scattered close to a tidal inlet on a flat plain elevated 1-2m above the high tide water level, reaching up to 140m inland. Most boulders had oyster shell remnants over their surface, which suggests that they were dragged from the nearby shore. The tsunami also brought a sheet of medium to coarse grained sand, with thickness ranging from a few mm up to 37cm. The distribution of deposits was mainly controlled by the existing topography. Another group of granite boulders was found between 150 and 300m from the coastline, at elevations of 2m and more. Their size reached 5.5m³. This second group of boulders may have been transported by an ancient tsunami.
Our paper reports results of a study on the bioavailability of selected elements from sediments deposited by the tsunami event of 26 December 2004 in south Thailand. In January 2005, 15 samples of the sediments deposited by the tsunami were collected at four different localities. The reference sample was collected in an area not affected by the tsunami. In the acid leachable sediments fraction (the bioavailable fraction) the contents of 27 selected elements (Be, Ga, Bi, Rb, Cs, Sn, Mn, Re, Co, Rh, Ru, Mo, V, Nb, Ta, Zr, Sc, Th, Pt, La, Ce, Nd, Eu, Gd, Tb, Ho, Lu) were determined using ICP-MS. The measurements were repeated after one year to establish a potential effect of the rainy season on the content of these elements in this fraction.
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