The Indian Ocean stretches from the shores of India on the north to the shores of Antarctica on the south. Africa is its western boundary, and Indonesia is on the east. Accounting for approximately 20 percent of the water on the Earth’s surface, the Indian Ocean is the third largest ocean in world. It has the fewest trenches of all the oceans and contains ridges that separate tectonic plates. One of the ocean’s trenches was responsible for the cataclysmic 2004 series of tsunamis in India and Indonesia.
Southwest India Ridge
The Southwest Indian Ridge in the far southern region of the Indian Ocean forms the boundary between the African tectonic plate and the Antarctic tectonic plate. The ridge stretches from the southwestern area of the Indian Ocean to the southern Atlantic Ocean, south of the cape of the African continent. The ridge is a divergent tectonic boundary, meaning that the plates are moving away from each other.
A divergent tectonic ridge that forms the boundary between the African plate and the Indo-Australian plate is called the Carlsberg Ridge; it runs along the eastern coast of the Africa in the western Indian Ocean. The ridge, seismically active, is named separately from the Southwest Ridge because of its individual seismic activity. A major earthquake of 7.6 on the moment magnitude scale occurred on the ridge in 2003.
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Southeast India Ridge
The Southeast India Ridge, which separates the Indo-Australian tectonic plate and the Antarctic plate, extends from the far southern area of the central Indian Ocean to the far western edge of the Pacific Ocean off the southern coast of Australia. The ridge is a divergent tectonic boundary as the two plates are moving away from each other.
One of the two trenches in the India Ocean is called the Diamantia Trench, which is in the southeastern basin of the India Ocean. Its maximum depth is more than 8,000 meters, or almost five miles, and it is the deepest spot in the Indian Ocean. “Diamantia Deep” is the name given to the deepest part of the trench, located 1,000 kilometers (621 miles) west-southwest of the city of Perth in Australia.
The Sunda Trench, the most-famous and most-destructive area of the Indian Ocean, was once called the Java Trench. Located in the northeastern corner of the Indian Ocean, the famous trench is the source of the 9.0 earthquake that in 2007 caused the destructive tsunami in Indonesia and India. At its deepest, it is more than 7,700 meters, or almost five miles deep. The Sunda Trench, the boundary between the Indo-Australian plate and the Eurasian plate, is part of the Ring of Fire of earthquake activity around the edges of the Pacific plate.