Thursday, October 31, 2019

Geology Of India TV Series- Coral Islands Episode

There is a 13 part series on the geology of India being shown on DD National, a Government of India run channel. In 2016, Vigyan Prasar, an autonomous organization under Department of Science & Technology  had commissioned Pulse Media,  a New Delhi based television production company, to shoot and produce the series.

This is really a commendable decision to give earth sciences the attention it deserves and to try to bring this fascinating field to a broader audience.

But the one episode I've seen so far has been disappointing.

Last Saturday I saw the episode on Lakshadweep Islands and was shocked to see that its depiction of the geological evolution of the islands was factually wrong. The episode describes the formation of volcanic islands (Laccadive Ridge) in the Arabian Sea west of the State of Kerala. The map shows the location of the Laccadive Ridge and adjacent basins relative to the present west coast of India.

 Source: Kerala-Konkan Basin: Directorate General of Hydrocarbons, Govt. Of India.

The audience learns through narrative and a graphic that prolonged volcanism around 66 million years ago resulted in lava piling up on the sea floor and eventually sticking out above sea level forming islands. In the Quaternary Period ( beginning 2.6 million years ago), coral colonies then formed in the shallow water around these islands. The islands then subsided, leaving behind rings of coral reefs encircling deeper lagoons. This explanation (first proposed by Darwin) applies to younger oceanic volcanic regions like the S. Pacific where thermal subsidence over the past few hundred thousand to few million years has promoted the formation of the classic reef and atoll system.

Volcanism in the Laccadive region stopped by 60 million to 55 million years ago. Any thermal effects would have long vanished. In any case, there is no evidence that the Laccadive ridge ever was an island chain. It is considered a submarine volcanic ridge. This ridge actually originated when the Indian continent broke away from Africa. The western continental margin of India was faulted and a series of ridges and depressions were formed due to block movements along faults. The Laccadive Ridge is one such 'structural ridge'. These structures formed by late Cretaceous times (90 million to 66 million yrs ago), and may have been rejuvenated from time to time.

Volcanism then poured lava on top of this ridge and over adjoining regions too. As the sea floor rises here forming a topographic high, the seas above it are shallow. Conditions favorable for calcium carbonate shell secreting organisms have persisted for millions of years. As a result, on this undersea volcanic foundation, a thick pile of limestones has accumulated over the past 50 million years.  Sediments ranging in age from the Eocene to the Pleistocene underlie the present day coral reefs.

The cross section shows the stratigraphy (sedimentary sequence) of the Laccadive Ridge and adjacent regions.

Source: Kerala-Konkan Basin: Directorate General of Hydrocarbons, Govt. Of India.

The present system of living corals has nucleated on a foundation of Pleistocene limestone. They did not form surrounding 'volcanic islands'. Coral blocks and sand originating from dead corals and other shell producing organisms has been moved by currents and has piled up above sea level forming the Lakshadweep Islands. The initiation of coral growth is really tied to creation of appropriate water depths as a result of sea level changes occurring repeatedly over the Quaternary Period due to the waning and waxing of ice ages. It has nothing to do with subsiding volcanic islands.

I was really surprised to see that a factually wrong scenario passed the filters of the subject experts credited in the episode. Did they not peruse the final script? The episodes are of 25 minutes duration. I can understand a need for brevity and simplicity of explanation.  But scientific accuracy is more important and cannot be sacrificed in pursuit of brevity. I do hope accuracy is not a victim in the remaining episodes too. The series is being shown on Saturday evening at 530 pm IST on DD National.

Disclosure: Pulse Media had hired me as a consultant to do background research for this television series. Needless to say I am disappointed that the inputs I had sent regarding the geological evolution of Lakshadweep were not included in the episode.

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