an ocean bordered by Africa in the west, Asia in the north, and Australia in the east and merging with the Antarctic Ocean in the south. Average depth: 3900 m (13 000 ft). Greatest depth (off the Sunda Islands): 7450 m (24 442 ft). In December 2004 a major undersea earthquake off Sumatra triggered a tsunami which affected large areas of the ocean as far away as east Africa, and killed an estimated 226 435 people. Area: about 73 556 000 sq km (28 400 000 sq miles)