An expert team of the Archaeological Survey of India (ASI) has found unscientific quarrying and dumping of overburden, mainly laterite, along the south-western flank of the Chembanmudy hillock in Naranammoozhy panchayat of Ranni taluk as the main cause of the landslip there on May 7.
There were no casualties in the landslip. It damaged two wells and nearly 100 metres of the Madanthamon-Arattumon-Pulickal-Edamuri road.
A two-member ASI team, comprising R. Sajeev, senior geologist, and Gaurav Kumar Singh, geologist, has said that the south-western flank of the Chembanmudy hillock was extensively quarried, causing unscientific changes in the hill slope and drainage channels.
A study report submitted by the ASI experts revealed that 15 first order streams originated from Chembanmudy, seven of them from its southern flank.
The ASI team observed unscientific drainage modification, extensive quarrying of the south-western flank, and huge dumps of manufactured sand (crushed granite) and granite chips produced by the crusher unit there along the hill slope.
The overburden was removed before the quarrying and deposited along the hill slope, without considering the slope stability.
This, coupled with the roads constructed for transportation of the quarried products, modified the course of three first order streams on the south-western flank, the report said.
It said the loose overburden deposited along the slope was highly unsorted, and ranged in size from clay to boulder.
The dumping of overburden and quarry-related activities had badly altered another first-order natural stream originating from this flank.
The report said concrete water storage tanks constructed near the buried stream-course put more pressure on the loose overburden.
It cited a large pond created by the quarrying at an elevation of 275 metres above mean sea level. The pond was separated from the break-in slope of the hillock by a 9-metre thick column of earth material. The report said the engineering properties of the separating column should be immediately studied, along with the water holding capacity of the pond.
Chances of a catastrophic pond-break could not be ruled out during the rains if the separating column containing filled debris failed to withstand the heavy pressure of the huge volume of water.
The ASI team strongly recommended that no blasting activity be allowed without considering future threats and corrective measures.
