Central Thailand / Bangkok

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Cordillera (Tanen Tong Dan) runs from the upland area of northern Thailand south to the Malay Peninsula; in the north lie mountainous uplands; in the south the outer edges of the Khorat Plateau (Dong Phaya Yen mountain range).

The landscape of the wide valley is characterized by terraced hillsides and the fertile alluvial plain that has been cultivated for centuries, mainly as paddy fields. Typical of this countryside are the many villages with wooden houses built on stilts owing to the constant danger of flooding.

The low-lying situation of the Menam Basin means that the tides reach far inland (Bangkok is only 2 m (6 ft) above sea level). This results in severe flooding during the monsoon rains of October and November with the entire plain and even large areas of Bangkok being under water. In the long term Bangkok will be seriously at risk if a further melting of the polar ice caps should produce a rise in sea level.

The Menam Basin is divided into two geomorphological zones: whereas an upland area with hills over 500 m (1640 ft) rises to meet the mountains in the north of Thailand the main part of the basin is an alluvial plain with the occasional steep limestone peak towering above it, such as that at Lopburi. The central plain is geologically recent, being formed predominantly from giant masses of sediment carried by the Menam Chao Phraya. Geological boreholes indicate that the sediment reaches depths of 400 m (1312 ft) around Bangkok. These alluvial deposits cause a considerable siltation of the river delta, which is expanding into the Gulf of Thailand at the rate of five to six meters a year.