ISSN: 1391 - 0531
Sunday, January 21, 2007
Vol. 41 - No 34

Grave problem of gravity

By Kumudini Hettiarachchi

For Sri Lanka, the past two years have been filled with tragedy, with nature venting its fury in different forms.

What has been in the news most are landslides, earthslips and floods which have left a trail of death and destruction. Just last week 17 people were killed and swathes of hills sliding down have become common sights.

All this is due to major changes in gravity, says scientist H.G.S. Ariyaratne who has been poring over documents in a bid to pinpoint why Sri Lanka has faced landslides in quick succession.

It all started with the powerful earthquake that rocked the seabed off the coast of Indonesia, explains Mr. Ariyaratne who is attached to the Landslide Studies and Services Division of the National Building Research Organization (NBRO). That was also the earthquake which triggered the deadly tsunami of December 2004 which left nearly 40,000 dead in Sri Lanka.

When studying all the data collated by scientists worldwide it is clear that the earthquake had left in its wake a change in gravity. “In some areas gravity has reduced and in others it has increased. Sri Lanka falls into a zone where there has been a reduction in gravity,” he says producing a satellite map of the world from the Ohio University in America.

With the reduction in the pull of gravity, mountain soil has got loosened and this is causing frequent landslides even when there is a light shower of rain, says Mr. Ariyaratne.

Going back to the day of the tsunami — December 26, 2004, he says his investigations reveal that tremors were felt in Wewessawatte in the Badulla district, while in Walapone in the Nuwara Eliya district in addition to experiencing the tremors there had also been rock falls. Attributing it to the sudden gravity change caused by the earthquake, he says in December 2006, 40 line-rooms of estate workers in Wewessawatte were affected and people had to be relocated.

Attempting to prove his point further, Mr. Ariyaratne cites the example of landslides occurring in “unheard of places” such as Maggona in Kalutara, Kapala Kanda in Ja-ela, Kandana, Kirindiwela in Gampaha and Bahirawakande in Kataragama while there has also been a rapid increase in the number of such incidents in other areas prone to these disasters.

Warning that we should attempt to earmark areas made vulnerable due to such gravity changes, he urges that land-use patterns should also be studied thoroughly.

“We must take particular care of Sri Lanka’s reservoirs,” stresses Mr. Ariyaratne. All the reservoirs are in the hills and gravity change could impact severely on them, with landslides filling up the reservoirs with rubble which in turn will cause major flooding in the surrounding areas.

Mr. Ariyaratne’s plea to both the authorities and the people is: Let us be alert to the fact that the gravity change after the 2004 earthquake could have adverse impacts on Sri Lanka and take measures after research and study to prevent a catastrophe.

Sudden drop

In a report in the journal Science, scientists at Ohio State University and the University of California, Santa Barbara, report that in the aftermath of the 9.1 magnitude earthquake, the largest in four decades, Grace (Gravity Recovery and Climate Experiment) recorded a sudden drop in gravity near the quake’s epicenter off Sumatra.

The rupture raised thousands of square miles of the seafloor, reducing the density of rocks in the earth’s crust and diluting their gravitational pull. The data, combined with models of the earth’s interior, indicate that the density changes extend hundreds of miles. -New York Times

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Copyright 2007 Wijeya Newspapers Ltd.Colombo. Sri Lanka.