CONTINENTAL DRIFT ..................

EARTH QUAKES, TSUNAMIS AND CONTINENTAL DRIFT

N.Nandhivarman

Tsunami hit Pondicherry recently and people were taken aback at its ferocity. The least expected unfolding of the Nature’s fury has stirred a debate on the changes in our coastline. Why did it happen and how it happened are subjects of current debate. Earth’s surface rests divided into 12 plates. Now the 13 th plate is in the offing. Throughout history scientists believe continents to be drifting, moving closer, or breaking from one another. Pangaea, the most recent super-continent on Earth began to break 160 million years ago. Paul Hoffman, Professor of Geology at Harvard University opines that while Pangaea broke up the Atlantic Ocean opened splitting North America from Eurasia. Then North America parted from Eurasia subsequently South America from Africa, Australia, Antarctica and India separated from Africa creating the Indian Ocean. The same scholar says, “ Atlantic and Indian Oceans continue to widen while Pacific gets smaller. In 100 million years North America and Asia will probably drift into each other”. Paul Hoffman had already named the new super-continent as Amasia.

Jeffrey Welssel at Columbia University’s Lamont-Doherty Earth Observatory says, “ The result of this crucial stage in the collision between India and Asia is the breakup of the Indo Australian Plate into separate Indian and Australian plates”. He also said “ In The Central Indian Ocean Nature is conducting a large scale experiment for us, showing us what happens to oceanic lithosphere (earth’s outer layer) when a force is applied.” This experiment had its repercussions, when on fault lines earthquakes hit almost exactly where Indo Australian plates have broken.

 Group of researchers from NASA’s Goddard Space Flight Center have provided with schematic global tectonic activity map, which shows several types of faults, active spreading centers, and volcanoes. The fault-lines or geo fractures are areas where we must watch and take all precautions in constructions to save lives.

This may be a global watch, but Pondicherrian’s have specific areas to observe. A Report on Ground Water Survey and Exploration in the Union Territory of Pondicherry and its environs by a team of experts from Central Ground Water Board, Southern region in March 1973 says that “ The photo-geological study has also confirmed the existence of the fault to the west of the coastline a straight scarp running almost parallel to Pondicherry- Markanam Road” That finding was made three decades ago.

 Dr.S.M.Ramasamy Director of Center for Remote Sensing of Bharathidasan University as early as 1993 said, “ The East North East- West South West trending faults on the contrary are showing left handed (sinistrel) ongoing translational movements. Such sinisterly and dextrally moving faults display definite morph tectonic anomalies in the remotely sensed data and also in the field. In addition, there is a conspicuous land subsidence between Pondicherry in the North East and Cumbum valley in the South West.

 One such graben has been established along north east- southwest trending faults in between Pondicherry-Cuddalore in the northeast and Cumbum valley in the Southwest. It is significant to observe that the earthquake epicenters fall along such NE-SW trending fault in Cuddalore, Ariyalor, Dindigul and Kodaikanal.

 In view of a geo-fracture i.e. fault line from Kalapet in Pondicherry to Cumbum Valley in South Tamil Nadu, great caution must be taken in construction of high rise structures wherever fault lines have been identified. Earthquake resistant construction design in places where one fault line passes, as mentioned above, is need of the hour. There are pictures taken by satellites using remote sensing techniques had identified studies covering Tamil Nadu its and various fault lines. It is high time sky scrappers do not come up in the fault line and quake prone areas.

 While Earthquake precautions are need of the hour, the new threat to Tamil Nadu’s coast comes by way of Tsunamis. Tsunami is a known phenomenon in Pacific Ocean stretching from Chile in Latin America to Japan in Far East Asia. Seismic disturbances, coastal earthquakes, volcanic eruptions or under sea landslides that jolt the ocean floor cause tsunamis, which travels at speeds up to 500 miles per hour and reaches heights between 50 and 100 feet. Tsunami observatories and Earth Quake observatories must be set up for early warning systems. People living in low-lying coastal areas have faced the brunt. “ It is high time fishermen settlements are shifted to higher grounds. World Bank and global assistance that is forthcoming must be utilized to create fishermen colonies in high ground ’’opines Narambai Kanagasabai, President of Narambai Fishermen Panchayat of Pondicherry state.

 The green house effect causes rise in sea water levels. Scientists have predicted that by 2100 A.D the rise in sea level will be between 0.5 to 1.5 meters. Before 1.5 million years Sea was closer to Madurai and before 90,000 years Chennai, Pondicherry and Vedaranyam were surrounded by sea. Due to fall in sea levels 65,000 years ago India and Ceylon joined and when sea level rose around 27,000 years ago they parted. Then 17,000 years ago due to fall in water level both joined and when water rose they parted. This is the study-report of Bharathidasan University’s Earth Sciences Department. All these studies and past history makes it clear that our coastline had undergone changes over centuries. Poompuhar of Chola Empire is beneath the seas. Sirkazhi once a coastal town is now an interior town. So changes in our coast is continuous. Caution must be taken about all dwellings in our coast, and let this tsunami attack be an eye opener.

courtesy: The New Indian Express-weekend-1.01.2005

NANDHIVARMAN ON TAMIL NADU

THE SEA COAST EROSION

  Nowadays seas frighten the fisher folk. For centuries fisher folk had established unassailable bond of love with seas, but in post tsunami phase every change in the sea causes nightmare. The sea recedes and people become panicky. Waves enter villages lashing out the beaches. People run hither thither for safety. Kanyakumari to Cuddalore almost for a week people of the coast spent sleepless nights and anxious days. This scenario had waken up the social thinkers and scientists to look for solutions to coastal erosion. Changes due to continental drift is inevitable. Here too if we look at the projections made by scientists, the future world map of 100 million years and 250 million years show changes in India’s position but India always remain attached to the Asian continent. This should be viewed with consolation, because in past India was an island nation separated from Asia.

“Our planet is a tri-axial ellipsoid, moving around the Sun in an elliptical orbit at 30 kilometers per second and rotating around its axis at 1,666 kilometers per hour which is faster than speed of sound. Such high speed rotation has resulted in polar areas being compressed towards the center and equatorial areas being bulged out” says Professor Vishal Sharma. Apart from these changes the coast of Tamil Nadu had undergone variations in the past but the present causes more concern. As per study by the School of Earth Sciences of Bharathidasan University " Before 1.5 million years ago Sea extended up to Madurai. Around 90,000 years before Chennai, Pondicherry and Vedaranyam were encircled by seas. Since sea level subsided 65,000 years ago India and Ceylon got connected. When sea level rose by 27,000 years ago both parted and when it fell by 17,000 years before joined again to part again". And amidst panic, if we look at the map of coastal changes in Tamil Nadu, one could know that the coast instead of moving inwards  had extended seawards. This is enough to give us fresh hope for survival braving the fury of Nature.

 The sea erosion of coast is not an India specific problem. "More than 80 percent of the world shorelines are eroding at the rates varying from centimeters to meters per year." says Orrin.H.Pelkey, Professor of Geology and Director of the Program for the study of Developed Shorelines in the Duke University, North Carolina, USA. He had authored two books and one of its title has a message to all of us. " Living by the Rules of the Sea" is his book and it is high time we learn to live by the rules of the seas.

 A walk in the beach and breathing its salubrious breeze is world wide habit. But how many of those who visit beaches are aware on how beaches are formed ? People are worried about erosion. But it is a fact that without erosion beaches could not be formed. "Without the process of erosion, we would not have beaches, dumes, barrier beaches and the highly  productive bays and estuaries that owe their existence to the presence of barrier beaches" opines Jim O'Connell, the Coastal Processes Specialist of Woods Hole Oceanographic Institution. Well erosion might have helped beach formation, but it is sending alarm bells from Kanyakumari to Chennai and beyond. Let us look for some scholarly opinion in this regard. After a close study at the Pitchavaram forests near Chidambaram, M.S.Swaminathan Research Foundation reveals that "in between 1930 and 1970, the seashore had eroded by 550 meters. Between 1970 and 1992 the rate of erosion was about 12 meters." The writing on the wall is clear. In past Sirkazhi was a coastal town, which now is interior by kms. The Harbour of Choza Empire, Poompuhar is now beneath the seas. At present warning from Pitchavaram must awaken us. 

Apart from facing Nature's onslaughts with preventive measures , human errors too needs to be corrected. Sand is the food for beaches, and it is needless to say that our rivers are not supplying that food to the beaches. Human exploitation and drying of rivers depletes sand supply to beaches. Interlinking of rivers as often advised by our President A.P.J.Abdul Kalam will not only solve water crisis but will save dying beaches. 

Sea level rise is primarily due to the thermal expansion of the sea water and melting of the glaciers and ice caps. Artic Climate Impact assessment by 250 scientists says that “ global warming is heating the Artic almost twice as fast as rest of the planet ” United Nations sponsored Inter Governmental panel on climate change will be bringing out its fourth assessment by 2007. Changing Winds and currents in the Indian ocean in 1990’s contributed to the global warming says a NASA study in the Geophysical Research Letters. The recent lashing of waves of Tamil Nadu coast was triggered by a storm near Australia, scientists say. The National Hurricane Center of USA reports that “ hurricanes release heat energy at the rate of 50 trillion to 200 trillion watts. This is equivalent to 10 mega ton nuclear bomb exploding about every 20 minutes.” But we in India are in one way lucky. Our coast will not be hit by hurricanes. Our cyclones are less intense. Storms that hit continental America have almost the full width of Atlantic Ocean to gain strength, Since our cyclones emanate from Bay of Bengal there is neither room nor time for them to grow, and this natural phenomenon helps us in one way.  

Courtesy: The New Indian Express-weekend-4.06.2005