Andaman Sea

The Andaman Sea is a significant marginal sea located in the northeastern Indian Ocean.

Historically known as the Burma Sea, it occupies a vital position between 4°N to 20°N latitude and 92°E to 100°E longitude. The sea is bounded by the coastlines of Myanmar and Thailand. To the west, the Andaman Islands and the Nicobar Islands separate this basin from the Bay of Bengal. Its southern boundary reaches Breueh Island, just north of Sumatra. The Strait of Malacca serves as the southern exitway for the basin. This sea is a major hub for fishery and the transportation of goods.

The physical layout of the sea floor, or bathymetry, is quite varied. The northern and eastern sides are relatively shallow. This is due to the continental shelf extending from Myanmar and Thailand. About 45 percent of the basin area is shallower than 200 metres. The Irrawaddy River flows into the sea from the north through Myanmar. It delivers massive amounts of silt and mud into the water. This sediment makes the northern parts of the sea less deep. In contrast, the western and central areas are much deeper. Less than 5 percent of the sea is deeper than 4,000 metres.

Water moves between the Andaman Sea and the Bay of Bengal through specific passages. These are known as straits or channels. The most important ones are the Preparis Channel, the Ten Degree Channel, and the Great Channel. The Preparis Channel is the widest but also the shallowest of the three. It separates southern Myanmar from the northern Andaman Islands. The Ten Degree Channel is deep and sits between Little Andaman and Car Nicobar. The Great Channel is also deep and separates Great Nicobar from Banda Aceh. These channels control how water enters and exits the basin.

Deep beneath the ocean floor, tectonic plates are constantly moving. A north-south boundary exists between the Burma Plate and the Sunda Plate. These plates were once part of the larger Eurasian Plate. They became separate due to intense transform fault activity. This movement created a back-arc basin, which is a type of marginal basin. This process began forming the Andaman Sea approximately 3 to 4 million years ago. The boundary between these plates results in high seismic activity.

This tectonic activity can lead to powerful earthquakes. At least six earthquakes have reached a magnitude of 8.4 or higher. One of the most significant events occurred on 26 December 2004. A large portion of the boundary between the Burma plate and the Indo-Australian plate slipped. This caused a megathrust earthquake with a magnitude of 9.3. During the event, the sea floor was uplifted by several meters. This uplift generated a massive tsunami with very high waves. The disaster killed approximately 280,000 people along the Indian Ocean coasts.

Volcanic activity is another feature of this region. Barren Island is the only currently active volcano near the Indian subcontinent. It is located east of the Great Andaman island group. The volcano is about 90 km from the Andaman Islands. It is caused by the subduction of the India plate beneath the Andaman island arc. This process forces magma to rise through the Burma plate. Barren Island resumed activity in 1991 after being quiet for nearly 200 years. The island of Narcondam was also formed by this volcanic process.

The climate of the Andaman Sea is driven by the monsoons of Southeast Asia. This causes the prevailing winds to reverse twice a year. From November to February, the region experiences north-easterly winds. These winds are strongest in the western part of the sea. From May to September, the winds switch to strong south-westerlies. These winds are distributed fairly evenly across the entire basin. Air temperatures remain stable, staying around 27°C throughout the year. Precipitation is highest in the summer, reaching up to 3,000 mm per year.

Ocean currents and water properties also change with the seasons. In the winter, currents are generally south-easterly and easterly. In the summer, they become south-westerly and westerly. The water temperature at the surface averages around 28°C to 30°C. At depths of 100 metres and below, the temperature remains constant at 22°C. The salinity of the water also varies. In the northern part, salinity drops to 20–25‰ because of freshwater from the Irrawaddy River. In the south, salinity stays between 30.0 and 33.0‰.