In a phenomenon known as rock-weathering, a huge rock from the Kuravan hill, one of the two hills (the other being Kurathi hill) connecting the Idukki arch dam, rolled down 145 ft on Saturday to damage the ladder that connects the lower end of the dam to the upper end.
There was no human presence in the area, so a major accident was avoided. Two other rocks, which broke away from the hill with the one that fell, were seen precariously hanging at the middle of the hill. Efforts have been made to remove them. Another layer is all ready to peel off, and if it does, the down hill area of the dam faces the threat of damage.
It was on September 23 that a similar incident of rock falling was reported in the area. The rock that fell on Saturday was bigger in size than the one that fell last time.
The incident is the sixth after the 1993 rock-weathering reported in the hills near the dam. A chemical process aggravated by climatic changes, rock-weathering occurs when cracks develop on rocks after water that accumulates between the different layers is subjected to climatic variations swinging between high daytime temperatures and low night-time ones.
As rock portions break away, nearby portions of the rock also face the threat as time passes. Loose soil could also aggravate the process.
The usual process followed to counter rock-weathering is removing the upper layers and exposing the strong portion of the rock. This could stop the rock getting weak to some extend and also prevent rock-weathering, according to an official at the Geological Survey of India (GSI).
After rock-weathering last September, scientists of the GSI and Kerala State Electricity Board engineers supervised the work on removing the weak layers of the rocks on the hills and cleared the earth that was also prone to falling downhill. If timely clearance of the weak layers of the rocks is not done, more rock-weathering could be expected in future. However, considering the large area of the hills on the two sides of the arch dam, it will be a tough task.
Minister visits dam
Electricity Minister M.M. Mani with senior KSEB engineers visited the area.
The Minister directed the officials to take immediate measures to prevent rocks from falling to the ground. He said, if required, strong iron nets would be placed to protect the dam and the area from rock-weathering.
