Danger beneath our feet: Understanding sinkholes

SHAH ALAM - Imagine walking down a busy street, only to see the ground beneath your feet suddenly give way and vanish into the depths below.

This terrifying scenario is exactly what occurred recently at Jalan Masjid India, where a 48-year-old Indian national tragically fell into a sinkhole.

While this event has triggered questions about public safety, it's important to understand what causes these unpredictable phenomena, how they form, and the risks they pose to our communities.

What are sinkholes?

Sinkholes are sudden collapses in the ground caused by the erosion of soluble rocks, such as limestone, salt, or gypsum.

As groundwater flows through these rocks, it dissolves them overtime, creating underground cavities.

When the surface above can no longer support itself, it collapses, forming a sinkhole.

These geological phenomena commonly occur in areas with "karst terrain," where the bedrock, often dominated by limestone, is highly susceptible to erosion.

Unlike natural drainage systems, sinkholes accumulate rainwater before it seeps underground, contributing to their formation.

Where do sinkholes occur?

Sinkholes are particularly common in regions where limestone bedrock is prevalent, such as Malaysia and other parts of the world with similar geological compositions.

Urban areas are at a higher risk of sinkholes due to the heavy development that disrupts or overloads groundwater channels.

The American Geological Society stressed that limestone, a sedimentary rock composed mainly of calcium carbonate, is especially vulnerable to erosion due to its porous structure.

Overtime, acidic rainwater or groundwater dissolves the limestone, creating voids beneath the surface that eventually cause the ground to collapse.

Natural factors like heavy rainfall, drought, and shifts in water tables increase the likelihood of sinkholes, while human activities such as construction, mining, and drilling can accelerate their formation by destabilising the ground.

The United States Geological Survey emphasises that human interference often disrupts natural water drainage or increases water flow in vulnerable areas, contributing to sinkhole formation.

In the meantime, Malaysia Geological Society recommended refilling sinkholes and monitoring areas with unusual features, such as circular patches of green grass or standing water, for early signs of potential sinkhole activity to prevent disasters.

Previously, on October 14, 2000, four sinkholes with diameters ranging from 8.5 metres to 15.0 metres and depths from 5.0 metres to 10.0 metres suddenly appeared between Bukit Chuping and Bukit Cowder near Mata Ayer, Perlis.

From October 17 to December 2, 2000, a series of investigations were conducted, including aerial photography, surface and subsurface geological mapping (with geophysical surveys and Mackintosh Probe studies), hydrogeological analysis, and ground vibration monitoring.

These investigations revealed that all sinkholes, potential sinkholes, and related circular features were located within a 350-metre-wide zone trending east-northeast-southwest.

This zone, underlain by limestone, might extend from a fault zone observed at the southern end of Bukit Chuping.

Groundwater level monitoring showed a general flow towards the central area, where a depression formed near the largest sinkhole.

Blasting operations at the CIMACO Quarry were monitored for vibration, and results indicated low vibration levels in the study area, with additional minor but regular vibrations from heavy vehicle movements.

It is believed that light to moderate rainfall a few days before the sinkholes appeared may have added weight to the thin soil layers covering some voids, leading to their collapse and the subsequent formation of the sinkholes.

The dangers of sinkholes

Sinkholes can have devastating effects, swallowing vehicles, roads, buildings, and even people, as seen in the tragic incident at Jalan Masjid India.

These collapses pose significant risks to both human life and infrastructure.

On a larger scale, entire communities can be disrupted, with sinkhole-related damages sometimes costing millions of dollars.

In severe cases, residents may be forced to evacuate their homes.

How can we be more aware?

Raising awareness and education are critical in reducing the risks posed by sinkholes.

Residents living in areas prone to sinkholes should stay informed about local geology and remain vigilant for signs like small ground depressions, cracks, or changes in water drainage patterns.

Regular inspections of drainage systems, water pipelines, and surface structures can help detect potential issues before they escalate into major sinkholes.

By closely monitoring these warning signs, communities can take preventive measures to avoid damage or loss of life.

A growing concern

Sinkholes have been documented for centuries, with mentions of them dating back to ancient civilisations.

Historically, they were part of natural geological processes, but modern urbanisation and climate change have increased their frequency and severity.

In recent years, sinkholes have made headlines in countries like China, the United States, and Malaysia, prompting governments to reevaluate infrastructure planning in vulnerable regions.

Sinkholes are not merely geological anomalies but real dangers that can cause catastrophic damage within moments.

As cities expand and landscapes change, it's crucial to remain vigilant and proactive in mitigating these risks.

By understanding sinkholes and recognising the early warning signs, we can better protect ourselves and our communities from the unexpected threats they pose.