Adam's Bridge

Adam’s Bridge is a 48-kilometer chain of natural limestone shoals reaching from Pamban Island, off southeastern India, to Mannar Island, off northwestern Sri Lanka. The shoals divide the Gulf of Mannar to the southwest from the Palk Strait to the northeast. Some sections rise above the sea, and much of the surrounding water is only about one meter deep. For sailors this shallow barrier has long been an obstacle rather than a convenient crossing, since even small vessels must follow carefully surveyed channels.

Geology explains why India and Sri Lanka appear almost joined here. The Palk Strait is shallow, and during the Last Glacial Period, when sea levels fell far below their present height, the exposed floor formed a broad land connection between the two islands and the mainland. As the Holocene sea rose, the strait and the site of the shoals were submerged by roughly seven thousand years ago. Later changes in relative sea level left the ridge of sandstone and conglomerate shoals partly emergent. The surviving islands and reefs remain the subject of study because the feature is difficult to survey and its exact history involves local uplift as well as changes in ocean level.

The modern name probably entered use by the time of the Central Asian scholar al-Biruni, around 1030. In Hindu tradition the feature is Rama Setu, the “Bridge of Rama,” because the Sanskrit epic Ramayana tells how Rama’s army built a causeway toward Lanka to rescue Sita. The identification of epic Lanka with Sri Lanka became prominent in later South Indian political and religious history. The geological formation remains natural; the traditional story belongs to religious literature, and claims that it is an artificial construction are disputed by geologists. The shoals also shaped practical navigation. British surveyors examined the passages in the early nineteenth century, and repeated attempts were made to dredge a route for shipping between India’s east and west coasts. These works generally produced channels usable only by vessels of light draft. The shallows consequently remained a barrier that forced larger ships to sail around Sri Lanka. Adam’s Bridge joins geology, religious memory, and maritime history in a narrow landscape where the difference between land and sea is never stable over long periods.