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Evidence points to tectonic activity in Lanka
By S.U. Deraniyagala
Investigations conducted by the Archaeological Department under the direction of the writer in 1969-72 revealed traces of prehistoric human activity within coastal alluvia. Gravels and stone tools had been deposited at levels corresponding with the then existing sea levels.

The gravels with artifacts are today at considerable heights above the present sea level -15 metres at Bundala-Patirajawela dating back to 125,000 years and 8 metres at Bundala-Wellegangoda dating back to 80,000 years. Occurrences of ancient coastal gravels inland around Mankulam and on Aruakallu at 60-80 metres and at Minihagalkanda in Yala at 40 metres have yet to be scientifically dated. This phenomenon of uplifted shores has been attributed principally to pressures generated by tectonic factors within the past one million years or so as indicated by the presence of man-made tools within the gravels.

These findings were presented in publications of the universities of Cornell and Harvard in the U.S.A. and the Archaeological Department (Deraniyagala 1976, 1988, 1992). They were contrary to the prevailing view that Sri Lanka is situated in a stable tectonic environment.

An article by Professor C.B. Dissanayake on South Asian plate tectonics (the Daily News of December 31, 2004) corroborated the geo-archaeological evidence that was secured some thirty-five years ago and claimed that Sri Lanka was indeed in a region of potential tectonic instability.

Study of coastal uplift
In view of these indications, it is a matter of urgency that the rates of coastal uplift in Sri Lanka be investigated scientifically, using state-of-the-art methods. The locations for sampling have already been mapped out by the Archaeological Department and Dr Mohan Abeyratne, a scientist attached to the Central Cultural Fund trained at the Australian National University in radiometrically dating the sediments.

What is needed at present is the equipment for 'optically stimulated luminescence' testing. A project proposal has been submitted by Dr. Abeyratne to the Atomic Energy Authority and an estimate prepared for procuring the equipment. It is now necessary to implement an enhanced version of it; and, since the dating techniques are being regularly upgraded, a back-up from international scientific institutions and consultants would probably be needed.

This project could constitute an important component of the proposed Indian Ocean-rim earthquake monitoring programme. Since the said project is of direct relevance to risk assessment in developing the coastal regions of Sri Lanka, its rapid implementation should be a national priority.

(The writer is a former Director- General of Archaeology.)

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