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The tsunami of 2004 in the Indian Ocean transported thousands of meters-long boulders shoreward at Pakarang Cape, Thailand. We investigated size, position and long axis orientation of 467 boulders at the cape. Most of boulders found at the cape are well rounded, ellipsoid in shape, without sharp broken edges. They were fragments of reef rocks and their sizes were estimated to be < 14m3 (22.7t). The distribution pattern and orientation of long axis of boulders reflect the inundation pattern and behavior of the tsunami waves. It was found that there is no clear evidence indicating monotonous fine/coarse shoreward trends of these boulders along each transect line. On the other hand, the large boulders were deposited repeatedly along the three arcuate lines at the intertidal zone with a spacing of approximately 136m interval. This distribution pattern may suggest that long-lasting oscillatory flows might have repositioned the boulders and separated the big ones from small. No boulders were found on land, indicating that the hydraulic force of the tsunami wave rapidly dissipated on reaching the land due to the higher bottom friction and the presence of a steep slope. We further conducted numerical calculation of tsunami inundation at Pakarang Cape. According to the calculation, the sea receded and the major part of the tidal bench (area with boulders at present) was exposed above the sea surface before the arrival of the first tsunami wave. The first tsunami wave arrived at the cape from west to east at approximately 130min after the tsunami generation, and then inundated inlands. Our calculation shows that tsunami wave was focused around the offshore by a small cove at the reef edge and spread afterwards in a fan-like shape on the tidal bench. The critical wave velocities necessary to move the largest and average-size boulders by sliding can be estimated to be approximately 3.2 and 2.0m/s, respectively. The numerical result indicates that the maximum current velocity of the first tsunami wave was estimated to be from 8 to 15m/s between the reef edge and approximately 500m further offshore. This range is large enough for moving even the largest boulder shoreward. These suggest that the tsunami waves that were directed eastward, struck the reef rocks and coral colonies, originally located on the shallow sea bottom near the reef edge, and detached and transported the boulders shoreward. 相似文献
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Sandip More Rajarshi Rit Mahasin Ali Khan Dipak Kumar Paruya Suchana Taral Tapan Chakraborty Subir Bera 《Journal of the Geological Society of India》2018,91(3):301-306
Fossil leaf impressions and pollen grains comparable to modern Sloanea sp. of Elaeocarpaceae collected from the middle part of the Siwalik sediments (Geabdat Sandstone Formation; Pliocene) in Darjeeling foothills of eastern Himalaya are reported in the present communication. On the basis of macro morphological features, leaf remains are described as a new species Sloanea siwalika sp. nov. This is the first authentic record of the occurrence of leaf and pollen grains comparable to the genus Sloanea L. from the Cenozoic sediments of India and Asia as well. The recovery of this species and other earlier-described evergreen taxa from the same formation, suggests the existence of a tropical, warm and humid climatic conditions during the depositional period. The present study further suggests that after Pliocene the taxon might have shifted from Darjeeling Himalayan region to the adjoining southeast Asian land masses, due to possible climate change caused by post-Pliocene orogenic movement of the Himalaya. 相似文献
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Viyakarn Voranop Lalitpattarakit Wipada Chinfak Narainrit Jandang Suppakarn Kuanui Pataporn Khokiattiwong Somkiat Chavanich Suchana 《Ocean Science Journal》2015,50(2):475-480
The effects of pH reduction on the settlement and development of the coral Pocillopora damicornis were investigated. Three different pH treatments (pH = 7.6, 7.9, and 8.1) were used. In addition, water quality (temperature, salinity, total alkalinity) around the study site was monitored. The results showed significant differences in the settlement rates of Pocillopora damicornis larvae between pH treatments (p ≤ 0.05). A decrease in pH levels caused a strong decline in larval settlement rate. In addition, at pH 7.6 and 7.9, all larvae were unable to complete metamorphosis, and metamorphosis delay was observed. Field monitoring showed low fluctuation of all seawater parameters within 24 hours, and there was no difference between seasons. From this study, a strong negative effect of pH reduction on P. damicornis larvae was observed. Although the function of physiology is still not clearly understood, correlations are likely to exist.
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