On 23 Aug 2024, tragedy struck a visiting Indian national when she fell into a sinkhole that suddenly emerged along Jalan Masjid India, Kuala Lumpur. Relentless search and rescue efforts have followed but the victim has yet to be found. Meanwhile, a wastewater expert has expressed fears that the victim is unlikely to have survived the high speeds at which water flows along the sewer lines.
Sinkholes occur when an underground area can no longer accommodate the weight of its surface terrain. Simply put, these cave-ins are caused by erosion occurring beneath ground level. This phenomenon usually takes place in areas where the surface rock comprises limestone or other forms of carbonate rock, salt beds and other materials capable of being naturally dissolved by groundwater. As flowing water slowly chips away at subterranean foundations and destabilises the bedrock, hidden new caves emerge. These may collapse, creating sinkholes.
Underground erosion may arise both naturally or as a result of human activity. The movement of water is a ubiquitous natural force in our world. It not only shapes landscapes visible to us, such as karst pinnacles and sea stacks, but also creates hidden underground rivers and caves. Limestone terrains are particularly vulnerable to water erosion. Rainfall absorbs carbon dioxide from the soil before converging with the underground water, turning it slightly acidic. This waterflow erodes the limestone sub-terrain and creates a network of cavities and voids. The US state of Florida, which has a geographical terrain primarily composed of limestone, is particularly prone to cave-ins.
Many sinkhole accidents are also attributable to rapid urbanisation. For example, drought and high groundwater withdrawals may reduce the buoyancy of an area and trigger the sinking of sub-terrain areas into cavities. Similarly, changes to groundwater composition due to the introduction or removal of waterflows may flush out looser materials and precipitate sinkholes.
Faulty underground water pipes may also give rise to deadly urban sinkholes. Even a slight gap between these pipes is capable of introducing a large amount of water into adjacent soil, dislodging and eventually causing the subsurface to become unstable.
Despite the growth of cavities beneath the ground, no obvious signs of instability tend to appear above it. With many of our utility pipes placed directly below ground, the paving of roads and pathways often acts as a bridge above sinkholes, hiding insidious voids below. If a cavity is not discovered and resolved in time, the surface is likely to eventually give way and swallow everything above ground.
Although the existence of sinkholes underground is usually not apparent, several subtle signs may hint at a possible collapse of the sub-terrain. Cracks in a foundation, an inability to close doors and windows properly, and the appearance of ground cracks in circular patterns are all tell-tale signs of ground instability which may point to the potential emergence of a sinkhole
As the search for the woman continues, one user took to Facebook to share a journal from 2017 discussing sinkhole risks in various areas of Ampang and Kuala Lumpur.
The resulting maps for sinkhole susceptibility hazard zones data have been classified into 5 prone levels: very low, low, moderate, high and very high risk.
Based on the map shown, the Ampang area has relatively high and very high hazard falls at the centre and western part of the district. The study also found that KLCC and Pudu areas are also at a high risk for sinkholes. This is due to the presence of limestone, marble, and acidic rocks, which are more prone to sinkholes. Meanwhile, TTDI is in the safe zone with the lowest risk.
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