Effect of the 2004 Asian tsunami in the sea cave of Tham Phaya Nak (Koh Phi Phi archipelago, Thailand) and possible evidence of a prehistoric event

Abstract

:Tsunamis may leave traces on the landscapes whose study provides a prehistorical approach and the analysis of possible recurrences. In karstic areas, caves and speleothems are good recorders for natural or anthropogenic events. They preserve traces of fragile remains as prehistoric paintings and they have been used for palaeoseismology studies. The effects of the 2004 Asian tsunami on the karstic shores have been studied in Western Thailand, close to Phuket. Limestone cliffs of Koh Phi Islands and the marine cave of Phi Phi Leh have been poorly affected, but a prehistoric-event has provoked the deposit of a layer of coral fragments into the cave. This damage could be attributed to a tsunami but a storm cannot be excluded.© 2010 Lavoisier SAS. All rights reservedKeywords: tsunami, karst, coral, speleothems, cave PresentationA major tsunami may provoke the transport of large boulders on variable distances or the deposit of marine sediments: sand, sea shells, coral fragments, several hundreds of meters inland. These morphological effects, and the deposits related to historic events, have been studied since a long time, and many attempts were done to attribute a tsunami cause to marine sediments present on shore. The researches on continental deposits were initiated by Attwater, [1] in Oregon and Dawson et al.,[2] in Scotland. A great number of studies were conducted all over the word ever since.Deposits of coral boulders or coarse clasts and sand, tens to hundreds of meters inland are frequently attributed to prehistoric tsunamis [3,4,5,6,7,8,9].Meanwhile Dawson and Stewart [10] pointed out that evidence of tsunami impact has poor preservation potential, being often difficult to identify except for the largest ones [11]. In a study on several Carribean islands, Morton et al. [12] show that deposits previously attributed to tsunamis are depositional complexes, several centuries old, and are not entirely the result of tsunamis, but involve important storms.Except tsunamis, different mechanisms may explain the presence of marine sediments or blocks inland, sometimes at high altitudes: glacio-eustatism, hydro-isostasy, glacioisostasy, tectonics, storms.If geological or paleogeographical data are available, the question of tectonics or eustatism may easily find answers, but the storms effects are more difficult to estimate. A systematic sedimentological approach is needed to distinguish between 80Eric Gilli / Geodinamica Acta 23/1-3 (2010) [79][80][81][82][83][84][85][86][87][88] storm and tsunami deposits. Recent works focused on tsunami effects after the Papua New Guinea (1998) [3,14], and the Indian Ocean (2004) events [15,16] and several research axis were defined to characterize the sedimentary features of tsunami deposits [16]. The importance of the backwash is outlined [17,10] and several criteria were defined by different authors, as internal stratification of the deposit [15], sediment grain size [18] and micropaleontology [19,20].Boulder complexes deposited by tsunamis are easier to study [10];...

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“…In 2004, Koh Phi Phi Don was badly impacted by a Tsunami damaging nearly the entire tourism infrastructure located on the sand strip connecting the two islands. The waves of the tsunami approaching Koh Phi Phi were up to 6 metres above normal sea level, leading to the destruction of or severe damage to all houses situated below 5 metres of altitude (Gilli, 2010). Local houses made of light materials were swept away and even concrete houses suffered severe impacts (Gilli, 2010).…”

“…The waves of the tsunami approaching Koh Phi Phi were up to 6 metres above normal sea level, leading to the destruction of or severe damage to all houses situated below 5 metres of altitude (Gilli, 2010). Local houses made of light materials were swept away and even concrete houses suffered severe impacts (Gilli, 2010). The event led to a loss of around 70% of all previously available guest rooms on the island (Calgaro et al, 2009).…”