Geological stress could have triggered landslip

By Our Staff Reporter

THIRUVANANTHAPURAM, NOV. 13. Preliminary scientific assessment of the devastating lanslip at Amboori on Friday has led to the inference that geological stress factors could also have played a critical role in the tragedy. Geoscientists suspect the existence of a fracture zone at the disaster site.

The initial version was that the landslip was triggered by a newly-constructed road across the middle of the hill. A team of scientists from the Centre for Earth Science Studies (CESS) who had visited the accident site on Sunday said the road could have acted as a dam across the hill since it did not have drains to divert the rain water flowing down from the upper slopes. The pressure exerted on it by the stored rainwater could have triggered the slip.

However, a section of scientists feel that the presence of fracture lines in the disaster zone reveals the existence of a geological fault. The fissures which have developed on huge rocks near the disaster site also add to their contention. They say tectonic shear forces could have activated a fracture on the slope leading to the landslip.

A senior scientist argued that the landslip had originated from a saddle much above the road, lending credence to the fracture theory. He said the huge volume of slush which had surged down the slope could have been generated only by aquifers inside the fracture and not from surface soil alone.

The irregular shape of boulders which had come crashing down also points to the existence of a fracture. ``Unlike boulders in the open which tend to become rounded by weathering, those caught in fractures are likely to have sharp edges,'' he said. The scientists assume that the houses caught in the landslip were located in the natural drainage through the slip line of the fracture. They suspect that the fracture zone extends hundreds of kilometres along the same direction.

The CESS director, Dr. Baba, said unusually heavy rain could have been an additional factor activating the landslip. ``The isolated heavy showers in Amboori a few hours before the tragedy could have triggered the landslip.'' He said denudation of the slopes and conversion of forests into plantations had led to soil instability making the Amboori area vulnerable to landslips.

``While big trees like teak enhance soil stability by striking roots deep into rock fissures, seasonal crops like tapioca and rubber with weak roots do not help to hold the soil.'' He said about 100 square kilometres of land in the Neyyar catchment area had been identified as landslip-prone on the basis of slope, drainage, soil thickness and vegetation studies.

But geoscientists feel that assessment of landslip- prone areas should take geological factors into consideration. They highlight the need for a network of ultra-sensitive seismographs to record micro tremors. All the seismographs currently in use are broadband based and hence incapable of recording tremors below 3 on the Richter scale.

The scientists maintain that slope studies should be accompanied by monitoring of the earth structure and compression loads on various types of rocks for identification of landslip prone areas.

Send this article to Friends by E-Mail

Section  : Southern States
Previous : Chithira Tirunal statue unveiled
Next     : Search continues for body