The boundaries of South Asia vary based on how the region is defined. South Asia's northern, eastern, and western boundaries vary based on definitions used, while the Indian Ocean is the southern periphery. Most of this region rests on the Indian Plate and is isolated from the rest of Asia by mountain barriers. Much of the region consists of a peninsula in south-central Asia, rather resembling a diamond which is delineated by the Himalayas on the north, the Hindu Kush in the west, and the Arakanese in the east, and which extends southward into the Indian Ocean with the Arabian Sea to the southwest and the Bay of Bengal to the southeast.