Gulf of Thailand

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Gulf of Thailand
Gulf of Siam
Gulf of Thailand.svg
Location of the gulf
Location Southeast Asia
Type Gulf
Primary inflows South China Sea
Surface area 320,000 km2 (120,000 sq mi)
Average depth 58 m (190 ft)
Max. depth 85 m (279 ft)

The Gulf of Thailand, historically known as the Gulf of Siam, is a shallow arm of the South China Sea[1] bordered by Cambodia, Thailand, and Vietnam.


The modern Thai name of the gulf is Ao Thai (Thai: อ่าวไทย,  [ʔàːw tʰāj], "Thai Gulf") and "Gulf of Thailand" has been adopted as the official name of the body by the International Hydrographic Organization.[2][when?] Its name in Malay and Khmer continues to be the "Gulf of Siam" (Teluk Siam and Chhoung Samut Siem, respectively). In Thai, the gulf is historically known as Ao Sayam (Thai: อ่าวสยาม).[3]

It is generally identified with the Great Gulf (Latin: Magnus Sinus) known to Greek, Roman, Arab, Persian, and Renaissance cartographers before the influx of Portuguese explorers removed the phantom Dragon Tail peninsula from European world maps during the 16th century.


The Gulf of Thailand is bordered by Cambodia, Thailand, and Vietnam. It occupies a seabed area of 304,000 km2 from 6° N to 13°30' N latitude and 99°E to 104° E longitude.[4]:250 The northern tip of the gulf is the Bay of Bangkok at the mouth of the Chao Phraya River. The southern boundary of the gulf is defined by the line from Cape Bai Bung in southern Vietnam (just south of the mouth of the Mekong river) to the city Kota Bharu on the Malaysian coast.

The Gulf of Thailand is relatively shallow: its mean depth is 58 metres (190 ft) and the maximum depth is only 85 metres (279 ft).[4]:250 This makes water exchange slow, and the strong water inflow from the rivers reduce the salinity in the gulf (3.05–3.25%) and enrich the sediments. Only at the greater depths does water with a higher salinity (3.4%) flow into the gulf from the South China Sea. It fills the central depression below a depth of 50 metres (160 ft). The main rivers which empty into the gulf are the Chao Phraya, including its distributary Tha Chin River, the Mae Klong, and Bang Pakong Rivers at the Bay of Bangkok, and to a lesser degree the Tapi River flowing into Bandon Bay in the southwest gulf.

Map showing the location of the gulf

The International Hydrographic Organization defines the southern limit of the Gulf of Thailand or Siam as "A line running from the Western extreme of Cambodia or Camau Point (8°36'N) to the Northern extreme of the point on the East side of the estuary of the Kelantan River (Lua error in Module:Coordinates at line 668: callParserFunction: function "#coordinates" was not found.)".[2]

Seabed Morphology

The seabed morphology in central depression of the Gulf of Thailand is characterised by presence of elongated mounds and ridges arranged parallel to the axis of the basin. This morphology, widespread within the Gulf of Thailand in water depths in excess of 50 m, covers an area of tens of thousands of square kilometres. It reflects an interaction between sediment dewatering and the erosional activity of the present-day bottom currents.[5] The sediment dewatering and fluid seepage result in the formation of numerous small pits and pockmarks. The long-term erosion imposed by currents of stable orientation modifies pockmarks into long runnels and depressions, and ultimately, leads to formation of the large fields of elongated mounds and ridges, as well as the residual outliers of un-eroded mud and clay sheets.[5]


Bay of Bangkok, Prachuap Bay, Ao Manao, Sattahip Bay.


The following are some of the most important islands in the gulf: Ko Samui, Ko Pha Ngan, Ko Tao, Ko Phaluai, Ko Sichang, Ko Lan, Ko Phai, Ko Khram, Ko Samae San, Ko Samet.


The Gulf of Thailand harbours many coral reefs that make it attractive to divers. The tropical warmth of the water attracts many tourists. Some of the most important tourist destinations in the Gulf of Thailand are the islands of Ko Samui and Ko Pha Ngan in Surat Thani Province, Pattaya in Chonburi Province, Cha-Am in Phetchaburi Province, Hua Hin in Prachuap Khiri Khan Province, and Ko Samet in Rayong Province. In recent years, the bay has become known for its whale watching activities, targeting the endemic, critically endangered populations of cetaceans (Eden's whales and Chinese white dolphins and Irrawaddy dolphins showing unique feeding behaviors) and dugongs.

Territorial disputes

The area between Malaysia, Thailand, Cambodia, and Vietnam is subject to several territorial disputes. Malaysia and Thailand have chosen to jointly develop the disputed areas, which include the islands of Ko Kra and Ko Losin.[citation needed] A long-standing dispute between Cambodia and Vietnam in the Gulf of Thailand concerns mainly the island of Phú Quốc or Koh Tral in Khmer, which is off the Cambodian coast.[6] Cambodia also claims 48,000 square kilometres (19,000 sq mi) of shelf area.[7]

See also


  1. Proceedings of the Royal Geographical Society
  2. 2.0 2.1 "47.—Gulf of Thailand (Siam)", Limits of Oceans and Seas, 3rd edition (PDF), International Hydrographic Organization, 1953, p. 23, retrieved 7 February 2010<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  3. ระยะทางเสด็จฯ ประพาสชายทะเลอ่าวสยาม พ.ศ. 2470 (pdf). Royal Thai Government Gazette (in Thai). Bangkok: Cabinet Secretariat. 88 (D): 44. 1927-05-22. Retrieved 2014-03-08. Unknown parameter |trans_title= ignored (help)CS1 maint: unrecognized language (link)<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  4. 4.0 4.1 Khongchai, Narongsak; Vibunpant, Somchai; Eiamsa-ard, Monton; Supongpan, Mala. "Preliminary Analysis of Demersal Fish Assemblages in Coastal Waters of the Gulf of Thailand" (PDF). Worldfish. Retrieved 19 Feb 2015.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  5. 5.0 5.1 Puchala, R. (2014), Morphology and origin of modern seabed features in the central basin of the Gulf of Thailand, doi:10.13140/RG.2.1.3891.0808<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  6. Prescott, J. R. V. (1978). Boundaries and Frontiers. Rowman and Littlefield. ISBN 0847660869.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  7. Paul Ganster & David E. Lorey, Borders and border politics in a globalizing world.

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