Sri Lanka lies on the Indian Plate, a major tectonic plate that was formerly part of the Indo-Australian Plate. It is in the Indian Ocean southwest of the Bay of Bengal, between latitudes 5° and 10° N, and longitudes 79° and 82° E. Sri Lanka is separated from the mainland portion of the Indian subcontinent by the Gulf of Mannar and Palk Strait. According to Hindu mythology, a land bridge existed between the Indian mainland and Sri Lanka. It now amounts to only a chain of limestone shoals remaining above sea level. Legends claim that it was passable on foot up to 1480 CE, until cyclones deepened the channel. Portions are still as shallow as , hindering navigation. The island consists mostly of flat to rolling coastal plains, with mountains rising only in the south-central part. The highest point is Pidurutalagala, reaching above sea level.