SHAH ALAM - The sinkhole at Masjid India is an example of an anthropogenic sinkhole, resulting from human activities rather than natural processes.
The revelation highlighted the growing impact of urban development on the city’s landscape, raising concerns about the risks posed by our actions beneath the surface.
Universiti Kebangsaan Malaysia (UKM) Geohazard and Engineering Geology Expert IR Dr Goh Thian Lai defined a sinkhole as a depression in the ground without any natural external drainage, meaning rainwater collects and drains into the subsurface.
"Sinkholes are most common in ‘karst terrain’ where the rock beneath the surface, such as limestone, gypsum, salt beds and other carbonate rocks, can dissolve naturally due to groundwater circulation.
"For example, Florida, which is largely underlain by limestone, is particularly susceptible to sinkholes. As rainfall seeps through the soil, these rocks dissolve, creating underground voids and caverns,” he told Sinar Daily when contacted yesterday.
Goh said that sinkholes could be dramatic because the land surface remained intact until the underground spaces became too large, causing a sudden collapse.
"The recent incident at Masjid India is an example of an anthropogenic sinkhole, caused by human activities rather than natural processes. The primary cause was the burst of a 1.5-metre sewer pipe, though the exact reason for the burst is unclear.
"As water flowed through the broken sewer pipe, it gradually washed away the backfill material beneath the walkway, creating a hollow space and leading to the sinkhole,” he said.
Goh said that natural sinkholes could also form due to factors like the rapid lowering of the groundwater table or ground vibrations caused by human activities such as piling, quarrying or major construction, as well as seismic activity.
"While Malaysia experiences mild tremors from earthquakes in Indonesia, local earthquakes triggered by fault reactivation can also contribute to sinkhole formation.
"In non-limestone areas, surface runoff from heavy rains is unlikely to cause sinkholes naturally. However, anthropogenic sinkholes can form if water infiltrates underground channels, tunnels, water pipes, drainage systems or sewer pipes.
"A rapid drop in the groundwater table can trigger both anthropogenic and natural sinkholes,” he said.
Meanwhile, in limestone areas, Goh said that the karst terrain naturally predisposed the land to sinkhole formation.
"KL, for instance, is underlain by the KL Limestone and Kenny Hill Formation, with limestone predominantly in the northern part of the city.
"For developments in areas underlain by limestone, extensive soil investigations are conducted to identify cavities and fractures. Field identification techniques, along with geophysical methods, are used to assess potential sinkholes.
"Once detected, engineering measures, such as injecting epoxy, concrete, or grout into the cavities, are implemented to prevent sinkholes from occurring,” he said.
The search for 48-year-old Indian tourist Vijayaletchumy, who fell into an eight-metre-deep sinkhole on Jalan Masjid India, continues.
Despite extensive search and rescue operations, including the use of scuba divers and a new flushing technique to clear blockages, no new leads have emerged.
Vijayaletchumy disappeared on Aug 23 while walking towards a nearby temple, with CCTV footage capturing the moment she vanished into the sinkhole.
Authorities have raised safety concerns but assured that Kuala Lumpur remains safe, with search efforts ongoing indefinitely until she is found.