The Indian Space Research Organisation (ISRO) has generated an undersea map of the Adam’s Bridge, also known as the Ram Setu, with the researchers saying their report is the first to provide intricate details about the structure.
“Our findings can aid in accentuating the understanding of Adam’s Bridge and its origin,” the researchers write in their study, published in the Scientific Reports journal on June 28. Since the bridge is mainly submerged in shallow waters, the researchers note, there has so far been minimal availability of ship-borne sounding data.
Adam’s Bridge or Ram Setu is a series of limestone shoals located between Mannar Island off Sri Lanka and Rameswaram or Pamban Island off Tamil Nadu.
Geological evidence suggests this underwater ridge used to be a land bridge joining India and Sri Lanka. In the 9th century AD, Persian sailors referred to it as ‘Setu Bandhai’, which means a bridge across the sea. The records from Rameswaram’s temples indicate that the bridge remained above the sea until 1480, when a cyclone destroyed it.
India and Sri Lanka were previously part of an ancient supercontinent known as Gondwana. India eventually separated and moved northward as a large island landmass until it collided with the supercontinent, Laurasia, around 35 to 55 million years ago, the researchers write in their study.
The structure holds immense religious significance among Hindus, as the Ramayana suggests it was built by Hanuman’s army of apes to help Ram reach Lanka to rescue his wife Sita from Ravan. It was named Adam’s Bridge by an East India Company surveyor general.
The mapping exercise of the bridge was conducted by researchers from ISRO’s Jodhpur and Hyderabad National Remote Sensing Centres using the NASA satellite ICESat-2, which is equipped with a photon-counting laser altimeter, enabling the scientists to measure the elevation of ice sheets, glaciers, sea ice, and other features with unparalleled accuracy.
The satellite bounced laser beams off the seafloor to determine that 99.98% of Adam’s Bridge is submerged in shallow waters, the study says.
Among other things, the ISRO researchers have confirmed that the submerged ridge is a “continuity” from Dhanushkodi in India to Talaimannar in Sri Lanka.
Findings Of ISRO Study On Ram Setu
The study highlights the uneven crest line of the ridge, lying under super-shallow waters and indicating sudden depth changes.
The scientists also discovered that the inclines on both sides of the bridge have different slopes, indicating that more sea material has encroached from the Gulf of Mannar as compared to the Palk Strait. The volume of Adam’s Bridge has been calculated to be about 1 km³, with only 0.02 per cent of this found to be above the average sea level.
Researchers used ICESat-2’s green laser, which can detect the sea floor up to 40 metres deep, in order to get depth information. This information enabled them to create a bathymetric (bathymetry is the study of beds or floors of water bodies) map of Adam’s Bridge, the researchers note. From this data, visual interpretations, including 3D-derived parameters, helped them confirm the physical characteristics of the bridge.
Furthermore, 11 narrow channels have been discovered along the ridge, which the researchers say facilitate water flow between the Gulf of Mannar and the Palk Strait, protecting the structure from being destroyed by waves.
The ISRO team notes in the study that Adam’s Bridge is subject to strong wave energy from both the Gulf of Mannar and the Palk Strait. Seasonal monsoon currents influence the water flow. The narrow channels along the ridge allow for free water exchange, reducing the impact of waves and helping maintain the structure’s integrity.