Strongly aligned coastal boulders on Ko Larn island (Thailand): a proxy for past typhoon-driven high-energy wave events in the Bay of Bangkok

© 2019 Institute of Australian Geographers Recent studies of elevated carbonate boulder deposits on several rock islands near Bangkok have indicated that Thailand\u27s capital city may not be as protected from typhoon strikes as previously thought. Here, new evidence is presented for past high-energy wave (HEW) events in the form of statistically significant patterns of boulder alignment on exposed rocky shorelines of Ko Larn island. The long-axis orientations of 193 coastal sandstone boulders were analysed across four study sites. Several scenarios for the unimodal, bimodal, and polymodal patterns found can be envisaged. Either the most recent HEW event was the strongest—in which case most clasts were rearranged unimodally (one observation site), or the strongest HEW event was earlier and subsequent weaker ones realigned only smaller boulders to produce bimodal or polymodal patterns (three observation sites). Inferred northeastward or eastward onshore flow directions are consistent with palaeo-typhoons penetrating into the Bay of Bangkok on northwestward curving tracks. The calculated minimum flow velocities required to transport all sampled boulders are 5.5–7.8 m s−1, similar to other findings throughout the Asia-Pacific region. It was observed that the absence of a fitted boulder geomorphology lends credence to the earlier proposed time frame of 150–200 years between typhoon phases in the upper Gulf of Thailand. The current work has provided additional insights into the characteristics of past HEW events that have a possibility of reoccurring again at some time in the future. Our findings continue to raise awareness for a reassessment of the risks of coastal hazards for the Chao Phraya River delta and densely populated Bangkok, for which storm surge modelling should be an urgent priority, so as to give better perceptions on how typhoon-driven marine incursion would impact the city

Urban coral reefs: Degradation and resilience of hard coral assemblages in coastal cities of East and Southeast Asia

© 2018 The Author(s) Given predicted increases in urbanization in tropical and subtropical regions, understanding the processes shaping urban coral reefs may be essential for anticipating future conservation challenges. We used a case study approach to identify unifying patterns of urban coral reefs and clarify the effects of urbanization on hard coral assemblages. Data were compiled from 11 cities throughout East and Southeast Asia, with particular focus on Singapore, Jakarta, Hong Kong, and Naha (Okinawa). Our review highlights several key characteristics of urban coral reefs, including “reef compression” (a decline in bathymetric range with increasing turbidity and decreasing water clarity over time and relative to shore), dominance by domed coral growth forms and low reef complexity, variable city-specific inshore-offshore gradients, early declines in coral cover with recent fluctuating periods of acute impacts and rapid recovery, and colonization of urban infrastructure by hard corals. We present hypotheses for urban reef community dynamics and discuss potential of ecological engineering for corals in urban areas

2004 Sumatra Tsunami

A catastrophic tsunami on December 26, 2004 caused devastation in the coastal region of six southern provinces of Thailand on the Andaman Sea coast. This paper summaries the characteristics of tsunami with the aim of informing and warning the public and reducing future casualties and damage.The first part is a review of the records of past catastrophic tsunamis, namely those in Chile in 1960, Alaska in 1964, and Flores, Java, Indonesia, in 1992, and the lessons drawn from these tsunamis. An analysis and the impact of the 2004 Sumatra tsunami is then presented and remedial measures recommended.Results of this study are as follows:Firstly, the 2004 Sumatra tsunami ranked fourth in terms of earthquake magnitude (9.0 M) after those in 1960 in Chile (9.5 M), 1899 in Alaska (9.2 M) and 1964 in Alaska (9.1 M) and ranked first in terms of damage and casualties. It was most destructive when breaking in shallow water nearshore.Secondly, the best alleviation measures are 1) to set up a reliable system for providing warning at the time of an earthquake in order to save lives and reduce damage and 2) to establish a hazard map and implement land-use zoning in the devastated areas, according to the following principles:- Large hotels located at an elevation of not less than 10 m above mean sea level (MSL)- Medium hotels located at an elevation of not less than 6 m above MSL- Small hotel located at elevation below 6 m MSL, but with the first floor elevated on poles to allow passage of a tsunami wave- Set-back distances from shoreline established for various developments- Provision of shelters and evacuation directionsFinally, public education is an essential part of preparedness