Andaman Sea

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Lore & Background

The Andaman Sea lies on the boundary between two tectonic plates, the Burma Plate and the Sunda Plate, which results in high seismic activity. Numerous earthquakes have been recorded, and at least six, in 1797, 1833, 1861, 2004, 2005, and 2007, had a magnitude of 8.4 or higher. On 26 December 2004, a large portion of the boundary between the Burma plate and the Indo-Australian plate slipped, causing the 2004 Indian Ocean earthquake. This megathrust earthquake had a magnitude of 9.3. Between 1,300 and 1,600 kilometres of the boundary underwent thrust faulting and shifted by about 20 metres, with the sea floor being uplifted several meters. This rise in the sea floor generated a massive tsunami with an estimated height of 28 meters that killed approximately 280,000 people along the coast of the Indian Ocean. The entire event severely damaged the fishing infrastructure. Within the sea, to the east of the main Great Andaman island group, lies Barren Island, the only currently active volcano associated with the Indian subcontinent. This island volcano is 3 km in diameter and rises 354 metres above sea level. Its recent activity resumed in 1991 after a quiet period of almost 200 years. The last eruption started on 13 May 2008 and continues.

Reader's Guide

The Andaman Sea has traditionally been used for fishery and transportation of goods between the coastal countries, and its coral reefs and islands are popular tourist destinations. However, the December 2004 Indian Ocean earthquake and tsunami severely damaged both the fishery and tourist infrastructure. The sea's northern and eastern parts are shallower than 180 meters due to the silt deposited by the Irrawaddy River, which flows into the sea from the north through Myanmar. Collectively, the modern Ayeyarwady (Irrawaddy) and Thanlwin (Salween) rivers deliver >600 Mt/yr of sediment to the sea. A major mud wedge with a distal depocenter, up to 60 metres in thickness, has been deposited seaward in the Gulf of Martaban. The western boundary of the Andaman Sea is marked by islands and sea mounts, with straits of variable depths that control water exchange with the Bay of Bengal. The most important straits are Preparis Channel (250 metres deep), Ten Degree Channel (600 metres deep), and Great Channel (1,500 metres deep). The climate is determined by the monsoons, with north-easterlies from November to February and strong south-westerlies from May to September, with mean wind speeds touching 8 m/s in June, July, and August.

Did You Know?

• The Andaman Sea is separated from the Bay of Bengal by the Andaman and Nicobar Islands and an associated chain of sea mounts along the Indo-Burmese plate boundary.
• The Strait of Malacca, which forms the southern exitway of the basin, is 3 kilometres wide and 37 metres deep.
• Barren Island, the only currently active volcano associated with the Indian subcontinent, resumed activity in 1991 after a quiet period of almost 200 years.
• The 2004 Indian Ocean earthquake had a magnitude of 9.3 and generated a tsunami with an estimated height of 28 meters that killed approximately 280,000 people.
• The modern Ayeyarwady and Thanlwin rivers deliver over 600 megatonnes of sediment to the sea annually.