Sinkholes: When the Ground Swallows Streets

Yesterday's Nightmare in Bangkok: A Street Vanishes in Minutes

At 7:13 AM on September 23, 2025, residents of Bangkok woke up to a nightmare scenario that sounds like something from a disaster movie. A massive sinkhole has opened up on Samsen Road, right in front of the well-known Vajira Hospital, startling residents and authorities in Bangkok. The collapse, about 30 metres wide and just as long, drops almost 50 metres into the ground.

Within minutes, the hole had swallowed part of the road, while a pickup truck teetered precariously on the edge of the hole. By 7:45 AM, two electricity poles and a tow truck from Samsen police station fell into the sinkhole as the collapse widened further. There were no casualties, but the collapse damaged three vehicles, according to Bangkok Governor Chadchart Sittipunt.

What caused this dramatic collapse? The massive sinkhole in front of Vajira Hospital in Bangkok on September 24, 2025, was caused by soil flowing into the Purple Line subway tunnel construction beneath the road surface. According to Governor Chadchart, the trouble began when the shallower tunnel developed cracks at a critical joint.

This recent Bangkok disaster isn't an isolated incident. It's part of a global phenomenon that's becoming increasingly common as urban areas expand and human activities alter the natural landscape. Sinkholes are appearing worldwide, swallowing cars, buildings, and entire sections of roadway with little warning. To understand why this happens, we need to dig deep into the science of what's beneath our feet.

What Are Sinkholes? Nature's Sudden Disappearing Acts

A sinkhole is a localized depression in the surface topography, usually caused by the collapse of a subterranean structure such as a cave. Think of the ground beneath your feet as having a hidden basement that you never knew existed. When that basement ceiling finally gives way, everything above it suddenly drops into the void below.

Sinkholes are usually circular and vary in size from tens to hundreds of meters in both diameter and depth, and in form from soil-lined bowls to bedrock-edged chasms. Some sinkholes develop gradually over years, creating gentle depressions that might go unnoticed for a long time. Others, like Bangkok's recent collapse, happen catastrophically in a matter of minutes.

The word "sinkhole" itself is descriptive: it's literally a hole where the surface sinks into the earth. However, this simple description overlooks the complex geological processes that give rise to these dramatic features.

The Recipe for Disaster: How Sinkholes Form

Understanding sinkhole formation is like understanding how to make Swiss cheese, except instead of bacteria creating holes in cheese, it's water creating holes in rock. The process requires specific ingredients that, when combined, can literally undermine the ground we walk on.

The Foundation: Soluble Bedrock

Their formation is most common in easily erodible karst terrains with carbonate rocks, like limestone or dolomite, or minerals known as evaporites, like salt and gypsum. These rocks have a fatal flaw: they dissolve in water. Limestone, which forms the foundation under many cities worldwide, is particularly vulnerable because it's made primarily of calcium carbonate, the same compound found in chalk and seashells.

When slightly acidic water encounters limestone, it creates a chemical reaction similar to dropping an antacid tablet in water. The rock slowly dissolves, grain by grain, creating cavities and cave systems beneath the surface. Over thousands of years, these cavities can grow into massive underground chambers.

The Catalyst: Water on the Move

Their formation is facilitated by high groundwater flow, often caused by high rainfall. When these thick, relatively soluble layers sit on top of insoluble rocks, significant underground streams (or even rivers) may form, dissolving a significant quantity of rock, creating large underground voids.

Water is the key player in sinkhole formation. As groundwater flows through cracks and joints in soluble bedrock, it gradually enlarges these openings. Sinkholes typically form when naturally acidic rainwater erodes underlying bedrock, creating damage beneath the surface.

Even normal rainwater is slightly acidic because it absorbs carbon dioxide from the atmosphere, forming a weak solution of carbonic acid. This natural acidity is enough to slowly dissolve limestone and other soluble rocks, especially when the water has time to circulate through underground systems.

The Karst Connection: Nature's Plumbing System Gone Wrong

Sinkholes are most common in what geologists call "karst terrain." These are regions where the types of rock below the land surface can naturally be dissolved by groundwater. Underground drainage systems, caves, and springs are characteristic of karst landscapes. They're essentially areas where nature has created its own underground plumbing network by dissolving the bedrock.

In karst terrain, surface water disappears into the ground through sinkholes and underground streams, travels through cave systems, and emerges at springs. This creates a landscape that's inherently unstable because the bedrock is constantly being dissolved and carried away by moving water.

Famous karst regions include Florida (which has thousands of sinkholes), the Yucatan Peninsula in Mexico, parts of China, and much of the southeastern United States. These areas are beautiful but geologically treacherous places to build cities.

Types of Sinkholes: Three Paths to the Same Destination

Not all sinkholes form in the same way. Geologists recognize three main types, each with its own formation process and characteristics.

Cover-Subsidence Sinkholes: The Slow Drainers

These sinkholes form gradually in areas where a layer of sand and clay covers the bedrock. As the underlying bedrock dissolves, the covering material slowly filters down into the voids below. The surface gradually subsides, creating a bowl-shaped depression.

Cover-subsidence sinkholes are usually not dangerous because they develop slowly, giving people time to notice the problem and take action. They're more like geological warning signs that something is happening underground.

Cover-Collapse Sinkholes: The Sudden Drops

These are the sinkholes that make headlines. In cover-collapse scenarios, a relatively strong layer of clay or rock acts like a roof over a growing underground cavity. This roof can hold up for years or even decades while the cavity below gets larger and larger.

Eventually, the roof becomes too thin to support its own weight plus everything above it. When it finally fails, the collapse is sudden and dramatic. The surface drops several feet or even tens of feet in a matter of minutes. This appears to be what happened in Bangkok, where construction activities weakened the "roof" over subway tunnels.

Bedrock Sinkholes: Direct Collapse

In areas where soluble bedrock is close to the surface with little or no soil cover, sinkholes can form directly in the rock itself. These often start as small depressions where water collects and gradually enlarge as the bedrock continues to dissolve.

Bedrock sinkholes are common in areas with exposed limestone, such as parts of the Appalachian Mountains or the karst regions of southeastern Europe.

The Human Factor: How We're Making the Problem Worse

While sinkholes are natural phenomena, human activities are dramatically increasing their frequency and severity. Although a natural process, the formation of sinkholes is often accelerated or triggered by human influences, such as broken drains, water mains and sewerage pipes, or modified drainage and diverted surface water; these wash sediment into the underlying materials, causing subsidence.

Urban Development: Loading the Surface

Cities are heavy. The weight of buildings, roads, and infrastructure adds stress to the ground below. When that ground is already weakened by underground cavities, this additional weight can trigger collapse.

Modern cities also change how water moves across and through the landscape. Concrete and asphalt prevent water from soaking into the ground naturally, concentrating it in drainage systems. This concentrated flow can accelerate the dissolution of bedrock and the formation of underground voids.

Infrastructure: Unintentional Water Management

Every city is riddled with pipes carrying water, sewage, and storm runoff. When these pipes break or leak, they can dramatically alter the underground water flow. A leaking water main can pump thousands of gallons per day into the ground, accelerating rock dissolution and washing away the supporting material around foundations.

The Bangkok sinkhole is a perfect example of this human factor. The collapse occurred directly above subway construction, where tunnel work had compromised the stability of the ground above.

Groundwater Pumping: Removing Nature's Support

Many cities pump groundwater for drinking water, irrigation, or industrial use. When large amounts of groundwater are removed from areas with soluble bedrock, it can destabilize existing cave systems and accelerate sinkhole formation.

Groundwater acts like a support system for underground cavities. When the water level drops, cavities that were previously stable may become prone to collapse. This has been observed in many areas where groundwater pumping has increased sinkhole activity.

Famous Sinkholes: When the Earth Opens Up

Sinkholes have been capturing headlines and terrifying communities around the world. Each major sinkhole tells a story about the interaction between geology, human development, and sometimes just bad luck.

The Guatemala City Disasters (2007 and 2010)

Guatemala City has experienced two massive urban sinkholes that shocked the world. In 2007, a sinkhole opened up that was 330 feet deep and swallowed several homes. Three years later, another sinkhole appeared, perfectly circular, approximately 100 feet across and 200 feet deep.

These sinkholes formed in volcanic deposits rather than limestone, showing that different geological conditions can create similar results. Heavy rains and poor drainage from tropical storms had saturated the volcanic soil, causing it to collapse into underground cavities.

The Daisetta, Texas Salt Dome Collapse (2008)

The sinkhole formed when an underground mound of rock salt collapsed. The sinkhole swallowed several cars, oil drilling equipment, and oil tanks. In one day, the Daisetta sinkhole had grown to 656 feet in diameter and 246 feet deep.

This sinkhole was particularly dramatic because it involved salt, which dissolves much faster in water than limestone. The collapse was likely triggered by groundwater infiltration that dissolved the supporting salt structures.

Florida: The Sinkhole State

Florida holds the unofficial title of America's sinkhole capital. The entire state is built on limestone bedrock, and sinkholes are a regular occurrence. Some of the most memorable include:

• The Winter Park Sinkhole (1981): This sinkhole opened up in a residential area and eventually grew to 350 feet wide and 75 feet deep, swallowing a house, part of a swimming pool, and several cars.

• The Seffner Bedroom Sinkhole (2013): Perhaps the most tragic recent sinkhole occurred when a bedroom floor collapsed, taking a sleeping man with it. The sinkhole opened directly under his bedroom in the middle of the night.

  
  

International Incidents

Sinkholes aren't just an American problem. They occur worldwide:

• China has experienced numerous dramatic sinkholes, including ones that have swallowed buses and buildings

• The Dead Sea region experiences frequent sinkholes as the water level drops and salt deposits dissolve

• The United Kingdom has sinkholes related to old mining activities and natural limestone dissolution

• Mexico's Yucatan Peninsula is famous for its cenotes, which are essentially water-filled sinkholes that were sacred to the ancient Maya

The Science of Prediction: Can We See Sinkholes Coming?

Predicting exactly when and where a sinkhole will form is one of the holy grails of geological science. While we can't predict individual sinkhole events with precision, scientists have developed methods to identify areas at risk and detect early warning signs.

Geological Mapping: Understanding the Foundation

The first step in sinkhole prediction is understanding what's beneath the ground. Geological surveys map the types of bedrock, the thickness of soil cover, and the locations of known caves and underground water systems.

Areas with the highest sinkhole risk typically have:

• Soluble bedrock (limestone, gypsum, salt) near the surface

• Active groundwater flow systems

• Thin or variable soil cover

• History of previous sinkhole activity

Remote Sensing: Watching from Above

Modern satellite technology and aircraft-mounted sensors can detect subtle changes in ground elevation that might indicate developing sinkholes. These techniques can identify areas where the ground is slowly subsiding before catastrophic collapse occurs.

LiDAR (Light Detection and Ranging) technology is particularly useful for detecting small depressions that might be the early stages of sinkhole formation. This technology shoots laser pulses at the ground and measures how long they take to return, creating incredibly detailed elevation maps.

Geophysical Surveys: Seeing Underground

Scientists use various techniques to "see" underground without digging:

• Ground-penetrating radar sends radio waves into the ground and analyzes the reflected signals to identify cavities and changes in rock structure

• Seismic surveys use sound waves to map underground structures

• Electrical resistivity measures how easily electricity flows through different materials underground, helping identify water-filled cavities

Monitoring Systems: Early Warning Networks

In areas with high sinkhole risk, scientists install monitoring systems to detect early warning signs:

• Tiltmeters measure tiny changes in ground angle that might indicate the beginning of subsidence

• Groundwater monitoring wells track changes in water level that might destabilize underground cavities

• GPS stations can detect millimeter-scale ground movement over time

The Bangkok Case Study: When Construction Goes Wrong

The Bangkok sinkhole provides a perfect case study of how human activities can trigger catastrophic ground collapse. Mr Chadchart said later the sinkhole formed above the Vajira Hospital railway station, at the junction between the tunnel and the station. The soil flowed into the tunnel, causing surrounding structures to collapse and a large water pipe to break, he said.

The Underground Construction Factor

Bangkok's Purple Line subway system required extensive tunneling beneath the city. This construction inevitably disturbed the natural soil and rock structure. When tunnels are excavated, they create new voids in the ground and can alter drainage patterns.

The sinkhole occurred at a particularly vulnerable location: the junction between a tunnel and a station. These junctions require complex engineering and are potential weak points where structural failures can occur.

The Domino Effect

Once the initial collapse began, it triggered a cascade of failures. As soil flowed into the subway tunnel, it removed support from the structures above. This caused power lines to fall, water pipes to burst, and vehicles to tumble into the growing void.

A roughly 160-foot hole pulled down power lines and exposed a burst pipe gushing water. The water from the broken pipe likely accelerated the collapse by saturating the surrounding soil and washing more material into the tunnel.

Urban Vulnerability

Bangkok's sinkhole highlights the vulnerability of modern cities to ground collapse. The sinkhole occurred in a dense urban area with critical infrastructure. A part of a road has collapsed in Bangkok, leaving a large sinkhole that disrupted traffic, damaged infrastructure, and prompted evacuations in the surrounding area.

The location near Vajira Hospital made the situation particularly serious, as it threatened access to critical medical services and required the evacuation of nearby residents.

Living with Sinkholes: Risk Management in an Unstable World

Since we can't eliminate sinkholes entirely, communities in vulnerable areas have developed strategies to manage the risk and minimize damage when collapses occur.

Building Codes and Construction Standards

Areas with high sinkhole risk often have special building codes that require:

• Deeper foundations that extend below potential collapse zones

• Flexible utilities that can accommodate ground movement

• Reinforced construction that can span small cavities

• Special inspection requirements before construction begins

Insurance and Financial Protection

Sinkhole insurance is available in high-risk areas, though it can be expensive. Florida, for example, requires insurance companies to offer sinkhole coverage, though property owners must specifically request and pay for it.

The insurance industry has become sophisticated in assessing sinkhole risk, utilizing geological data, historical records, and predictive models to determine rates and coverage limits.

Emergency Response Planning

Communities in sinkhole-prone areas develop specific emergency response plans that include:

• Rapid assessment teams to evaluate sinkhole stability and expansion risk

• Evacuation procedures for areas around new sinkholes

• Utility isolation procedures to prevent secondary hazards like gas leaks or electrical hazards

• Public communication systems to warn residents of developing situations

Engineering Solutions

When sinkholes do occur, engineers have developed various methods to stabilize them:

• Grouting: Pumping concrete or other materials into voids to fill cavities and provide support

• Underpinning: Extending building foundations deeper to reach stable bedrock

• Drainage control: Managing water flow to prevent further dissolution and cavity formation

• Load redistribution: Using structural techniques to spread weight over larger areas

The Future of Sinkhole Science

As urban populations continue to grow and cities expand into geologically challenging areas, sinkhole research is becoming increasingly important. Scientists are developing new tools and techniques to understand better, predict, and manage sinkhole hazards.

Advanced Monitoring Technology

New sensor technologies are enabling the real-time monitoring of ground conditions. Fiber optic sensors can be installed underground to detect tiny ground movements. Wireless sensor networks can provide continuous monitoring of groundwater levels, soil moisture, and ground stability.

Artificial Intelligence and Machine Learning

Researchers are using AI to analyze vast amounts of geological, hydrological, and historical data to improve sinkhole prediction. Machine learning algorithms can identify patterns and relationships that human analysts might miss.

Climate Change Considerations

Climate change is expected to alter precipitation patterns in many regions, potentially affecting sinkhole formation rates. Areas that become wetter may see increased sinkhole activity, while regions that become drier might see different types of ground instability.

Urban Planning Integration

City planners are increasingly incorporating sinkhole risk assessments into development decisions. This includes avoiding high-risk areas for critical infrastructure, designing transportation networks that can accommodate ground instability, and integrating sinkhole monitoring into innovative city systems.

Prevention and Mitigation: What We Can Do

While we can't prevent all sinkholes, there are steps that individuals, communities, and governments can take to reduce risk and minimize damage.

Individual Actions

Property owners in sinkhole-prone areas can:

• Learn to recognize warning signs like cracks in foundations, doors that won't close properly, or depressions in yards

• Maintain proper drainage around buildings to prevent water from pooling

• Have their property inspected if they notice potential warning signs

• Consider sinkhole insurance if they live in high-risk areas

Community-Level Measures

Local governments can:

• Conduct geological assessments before approving new developments

• Implement building codes appropriate for local geological conditions

• Maintain infrastructure to prevent leaks that can trigger sinkhole formation

• Develop emergency response plans for sinkhole events

• Educate residents about sinkhole risks and warning signs

Construction Industry Best Practices

The construction industry can:

• Conduct thorough geological surveys before beginning projects

• Use construction techniques appropriate for unstable ground conditions

• Monitor construction sites for signs of ground instability

• Implement quality control measures to prevent infrastructure failures that can trigger sinkholes

The Bigger Picture: Sinkholes and Society

The Bangkok sinkhole and others like it around the world represent more than just geological curiosities. They highlight the complex relationship between human development and natural processes, and the challenges we face as we continue to build cities in geologically challenging environments.

Economic Impacts

Sinkholes cause billions of dollars in damage worldwide each year. The costs include:

• Direct property damage from collapsed buildings and infrastructure

• Business interruption and lost productivity

• Emergency response and repair costs

• Insurance claims and legal settlements

• Decreased property values in affected areas

Social and Psychological Effects

Beyond the economic costs, sinkholes have significant social impacts. They can displace families from their homes, disrupt communities, and create lasting anxiety about ground stability. The sudden and unpredictable nature of many sinkholes makes them particularly traumatic for those who experience them.

Planning for an Uncertain Future

As the global population continues to urbanize, more people will be living in areas susceptible to sinkholes. This makes it essential to improve our understanding of sinkhole processes, develop better prediction methods, and create more resilient infrastructure.

The challenge is balancing the economic benefits of development with the geological realities of unstable ground. Sometimes this means avoiding certain areas entirely, other times it means accepting higher costs for specialized construction techniques.

Lessons from the Ground Below

Sinkholes remind us that the ground beneath our feet is not as solid and permanent as it appears. The Earth is a dynamic system where rock dissolves, cavities form, and surfaces can suddenly disappear without warning.

The Bangkok sinkhole serves as a dramatic reminder that urban development must account for geological realities. As cities continue to grow and underground infrastructure becomes more complex, the interaction between human activities and natural processes becomes increasingly important to understand and manage.

Whether formed by natural processes over thousands of years or triggered by human activities in a matter of hours, sinkholes represent one of the most visible examples of how the solid Earth beneath us is actually constantly changing. They're geological reminders that we're all just temporary residents on a dynamic planet that occasionally rearranges itself beneath our feet.

The key to living safely with sinkholes is understanding them, respecting them, and planning for them. As the science of sinkhole prediction and mitigation continues to improve, communities can better prepare for these dramatic geological events.

But the Bangkok sinkhole shows that even with our best efforts and modern technology, the Earth still has the power to surprise us with the sudden appearance of a very deep, very dramatic hole where solid ground existed just moments before.

In the end, sinkholes teach us humility about our relationship with the natural world and the importance of understanding the geological foundations upon which we build our lives. They remind us that solid ground is sometimes more of a temporary condition than a permanent guarantee.

Sources and Further Reading

Recent News and Case Studies:

• ABC News. "Bangkok road collapse creates a sinkhole disrupting traffic and prompting evacuations." September 24, 2025.

• NBC News. "Bangkok road collapse creates sinkhole, disrupting traffic and prompting evacuations." September 24, 2025.

• Khaosod English. "Bangkok Governor Reveals Massive Sinkhole Caused by Subway Construction." September 24, 2025.

• Bangkok Post. "Huge sinkhole appears in Bangkok." September 24, 2025.

Scientific Sources:

• U.S. Geological Survey. "Sinkholes." Water Science School. 2025.

• U.S. Geological Survey. "What is a sinkhole?" Frequently Asked Questions. 2025.

• National Geographic. "What causes a sinkhole to form?" October 19, 2023.

• Britannica. "What Causes Sinkholes? Formation, Water, Limestone, & Facts." April 22, 2025.

Government and Educational Resources:

• British Geological Survey. "Understanding sinkholes and karst." June 9, 2021.

• National Geographic Education. "Sinkhole." Resource Library. 2025.

• ZME Science. "What are sinkholes: how they form and why they're so dangerous." May 21, 2023.

Academic Research:

• ScienceDirect. "Sinkhole formation mechanisms and geostatistical-based prediction analysis in a mantled karst terrain." February 21, 2018.

• Geology Science. "Sinkhole | Formation, Types, Occurrence." April 23, 2023.