A shallow strait once linked India and Sri Lanka as dry land
Palk Strait sits between Tamil Nadu’s Pamban Island and Sri Lanka’s Mannar Island, joining the Bay of Bengal to the Laccadive Sea. Ram Setu—Adam’s Bridge—chains low islands and shoals along one edge. Central depths average about twenty metres, yet around the shoals water can be only one to three metres deep.
The strait runs between Pamban Island, at the south-eastern tip of Tamil Nadu, and Mannar Island in Sri Lanka’s Northern Province, opening north onto the Bay of Bengal and south onto the Laccadive Sea. Palk Bay forms its south-western lobe, about 137 kilometres long and between 64 and 137 kilometres wide. On one flank lies the chain of shoals called Ram Setu, or Adam’s Bridge; beyond them spreads the Gulf of Mannar. Rivers including the Vaigai drain into these waters.
Reefs, islets and shallows make passage hard for large vessels, although fishing boats and other small craft move freely. A shipping channel was first put to the British administration of India in 1860, and several commissions studied the idea afterwards. The most recent, the Sethusamudram Shipping Canal Project launched by the Indian government in 2005, ran into objections rooted in religion.
Those objections stem from the Ramayana, in which Rama’s army of vanaras builds a causeway across the sea to rescue Sita from the demon king Ravana; many Hindus see the shoals as its remains. Geology tells a plainer tale. When Last Glacial sea levels sat up to 120 metres lower, the whole strait was exposed ground, and rising Holocene waters drowned it by about 7,000 years ago.
Crossings have been engineered instead of dredged. The Pamban railway bridge opened on 24 February 1914, and a road bridge joined it in 1988. Trains stopped in February 2023 because of worries about the old structure, and a replacement rail bridge was completed in 2024. A fixed bridge or tunnel link between India and Sri Lanka has been floated since 2002 without being built.
Source: Palk Strait
