IPOH: Limestone hills in tropical areas which are exposed to human activities are capable of triggering sudden rock falls, a geomorphologist said today.
University Malaya's Dr Ros Fatihah Haji Muhammad said rainfall can lead to natural dissolution of rocks thus weakening the structure of limestone walls.
"Limestone hills in the tropics often form steep-sided walls due to natural collapse, and this can be observed in most of our limestone hills in Peninsular Malaysia.
"This process can be accelerated when there are solutions (rainwater) in the foothills.
"When rainwater flows into rock intercepts and natural dissolution occurs, the cracks between rocks widen, eventually triggering rock collapses," she told the New Straits Times today.
Dr Ros said, activities such as quarrying and tremors from other human activities could also speed up this natural process.
"The soil on limestone is usually thin and it often fills up the natural cracks. Losing this soil may further weaken the slopes.
Dr Ros also recalled the horrendous tragedy that befell "kacang puteh" traders and their families in Gunung Cheroh, Ipoh when a limestone cliff collapsed and crushed 42 people to death in 1973.
"In fact, there was another rock fall incident at the Lipis limestone cave in Merapoh a few days ago which was possibly triggered by limestone quarry activities in the past.
"Therefore, any development activities in limestone areas must strictly abide by the necessary guidelines," she said.
Earlier today, two guests at The Banjaran Hotsprings Retreat in Tambun here, lost their lives in a landslide.
Perak Mineral and Geoscience Department (JMG) deputy director Mat Niza Abdul Rahman said heavy rain since Nov 9 had weakened the residual soil on top of the limestone walls.
The structure eventually collapsed onto the villa where the victims were staying.
Meanwhile, Sahabat Alam Malaysia field officer Meor Razak Meor Abdul Rahman said limestone areas are very sensitive to development, especially for building permanent structures.
"Unlike granites, limestone rocks are porous stones and they easily erode.
"There is always ground-water movement in a limestone aquifer which could have long-term impact towards buildings," he said.
Meor also added, the Kinta Valley which constitutes mostly limestone areas, is sandwiched between the Titiwangsa and Kledang mountain ranges, which are largely made up of granite rocks.
"This is why Kinta Valley used to have a lot of tin ores, because streams running at the foot of the mountains will inundate the limestone valleys," he said.
"In fact, Kinta Valley also experienced many quicksand (tanah jerlus) incidents in the past due to development in limestone areas," he said.
Therefore, Meor advised the authorities to allow resorts and recreational centres to operate only if they clear a geological assessment by the Mineral and Geoscience Department (JMG).