IPOH: The 14 sinkholes which have appeared in several places in the state were partly caused by the recent earthquakes on the seabed off Sumatra. 

State Mineral and Geoscience Department director Mohd Noor Ayoob said the fact that the holes occurred immediately after the strong quakes pointed to this.

But the study of soil samples taken from the affected areas showed that other factors were involved as well, he told a news conference at the state secretariat yesterday. He had briefed Menteri Besar Datuk Seri Tajol Rosli Ghazali, who also attended the conference, on the situation.

"While the earthquakes have been identified as the main factor causing the sinkholes, at least three other factors were involved."

The geological setting of the Kinta Valley, which is made up largely of limestone, sand and mud, disturbance to the underground water movement and volume caused by recent heavy rainfall and poor drainage causing water to seep into the soil around and under the affected houses also contributed to the formation of the sinkholes, he explained.

The 14 holes measured from one to eight metres in diametre. The areas affected are Tronoh, Ipoh, Batu Gajah, Bukit Merah and Malim Nawar. All are disused mining areas.

Mohd Noor also gave a list of things to look out for which could mean that a sinkhole is about to form.

He advised residents in disused mining areas to pay attention to round depressions on the ground, which could indicate that the underlying soil structure had been weakened by underground water movement. A problem shutting windows was an important indicator that the soil underneath the house had been weakened as well as sudden cracks appearing on the walls.

He added the appearance of stagnant water on low ground and the sound of water movement under the house were warning signs of sinkholes. 

Tajol Rosli said 13 out of the 14 sinkholes appeared near older houses built without proper drainage systems, adding that the risk could be reduced if homeowners were to build drainage systems.

"Of course, since many of the affected houses were built on disused mining land, the risk of sinkholes will always be there because the soil under their homes was not rehabilitated," he said.