Tsunami strikes the coast with a great force. It is like a Boeing 707 plane crashing on the coast from offshore at full speed. The ravage of the tsunami was experienced by the peninsular East Indian coast on 26 December, 2004. The tsunami uprooted trees, parked cars were tossed like toys and boats berthed at the harbor were thrown hundreds of metres inland. A question that daunts the geologists is that were there tsunamis on the Indian on the Indian coasts in the past as well? Answer to part of this question we read last week. Now it is time to probe further.
The oceanographers were already concerned about global warming and accelerated sea-level rise and also the impact of cyclones on the coasts. The tsunami of December 2004, which was perhaps one of the worst disasters in the living memory, that took away nearly 2,00,000 lives gave impetus for the scientific community to study the possible evidences of such happenings in the historical past and pre-history as well.
In the course of their researches R. Nigam of National Institute of Oceanography (NIO) and R. Chaturvedi of National Centre for Antarctic and Ocean Research, Goa found something interesting on the coast of Kutch, off Gujarat. While searching for evidences of past storms in the off shore the drill cores revealed a sequence of sediments and foraminifers (marine organisms) that had finer sediments and smaller foraminifera at the top, report these scientists is a recent publication of the NIO. The normal deposition of the sediments undersea has finer sediments and smaller shells of dead organisms towards the bottom and the layers become gradually coarser upwards.
The sequence of sediments and organisms these scientists chanced upon had another story to tell. These sediments had been 'scooped' out from the deeper zones of the ocean and 'dumped' at the spot by waves with exceptionally high energy. These sediments confirm an age of around 10,000 to 12,000 years before present (B.P.) Based on the analyses of the sediments, radiometric dating and study of the organisms they conclude that some 8000 and 7000 years B.P. this part of the sea was exposed and the coast witnessed a major storm/tsunami.
Endeavors to find the clues of past tsunami are on in Indian Ocean elsewhere too. Costas Synolakis, Director of the Vitrebi School of Engineering Tsunami Research Center, Sumatra ays that having learnt the lesson from the Tsunami of 2004 they have become proactive to find further clues. It is anticipated that the 700 km long Sumatran coast can experience another big tsunami in coming three decades. What will be the magnitude of such a tsunami is difficult to assess.
The 2004 Tsunami was as a result of the megafault that extends much farther southeastward beneath the India Ocean just off the southwest coast of Sumatra. A rupture in this fault produced two great earthquakes and devastating tsunamis is 1797 and 1833. A repetition of such events can not be ruled out says Synolakis in one of his recent publications. Scary part is that the population of Padang, the worst affected area in past tsunamis was merely a few thousand, now it has about 800, 000 people there. As per the records the might of the 1797 tsunami was such that it tossed a 200-ton vessel in to the town approximately a kilometer upstream.
Researchers from Centre of Earth Science Studies, Thiruvananthapuram and their co-workers from the Archaeological Survey Of India and Wadia Institute of Himalayan Geology, Dehradun joined hands to explore the past tsunamis and found evidences similar to those uncovered by other Indian scientists engaged in collecting information on past tsunamis. C.P. Rajendran from the Center of Earth Sciences in one of his recent papers reports remains of ancient temples point towards probable tsunamis of the past. The high energy waves of the 26 December, 2004 tsunami exposed a 2000 year old brick temple on the beachfront near Saluvankuppam, just north of a famous World Heritage site at Mahabalipuram. Early sea-farers referred Mahabalipuram as a town of the seven pagodas. Except the ancient temple built on hard rock and protected by a shore protection wall that escaped the wrath of the present tsunami the others are completely submerged today. Till a few centuries ago their tops were visible, that is why the name, seven pagodas!
The tsunami waves riding three to six metre above sea level invaded the beach and scoured circular depressions along the Mahabalipuram coast in 2004. These depressions are now filled with tidal water, say C.P. Rajendran and his co-workers. They suspect such scouring could have taken place in the past too. The wave action this time exposed the buried rock sculptures and temple basements. Huge stone constructions dating to 8th century AD at a depth of 6-15 m underwater at about 600 m distance from the present shore temple came to their notice. Shoreline in this region is a receding one and Rajendran and his team estimate that the buried temples were about 800 m onshore around 1000 years ago. This team reports two levels of temples. Foundations and rock inscriptions of a brick temple that dates back to more than 2000 years are seen overlain by a 9th century temple made of granite.
What is interesting is the presence of sea shells and assorted debris over the brick foundation. Such accumulations are possible only when the shells and debris are scooped from depths and dumped by the giant waves. The evidences indicate that the temple was destroyed by a giant tsunami. The granite temple which came up on this site too was destroyed by yet another tsunami confirmed by the presence of sediments of the deeper sea.
The secrets of the buried temples were unveiled by the recent tsunami. There could be many more secrets pf the past under the vast oceans. May be they are uncovered before another tsunami strikes!