🚨 Sinkholes: Causes and Response Methods for Urban Disasters

Today Korean Social News | 2025.03.26

📌 Sinkhole Appears in Middle of Gangdong District Road, Motorcyclist Dies

💬 A sinkhole with a diameter and depth of 20 meters each occurred on a road in Gangdong District, Seoul on the 25th. Motorcyclist Park (33) was found dead after being buried for 17 hours. Fire authorities faced difficulties during rescue operations due to upper surface cracks and groundwater leakage. Authorities are investigating whether the Seoul Metro Line 9 extension construction and damage to underground utilities are the causes. Residents are expressing anxiety about additional accidents.

Summary

• A sinkhole is a phenomenon where the ground suddenly collapses after an underground cavity forms; in urban areas, they mainly occur due to damaged underground facilities or construction.
• Urban sinkholes are difficult to predict because preliminary signs are minimal, and they can cause life and property damage when they occur, making them dangerous.
• If you notice unusual signs such as road cracks or ground subsidence, report them immediately, and when a sinkhole occurs, maintain a safe distance and prepare for possible expansion.

1️⃣ Definition

A sinkhole is a phenomenon where soil or rock beneath the surface is eroded or lost, causing the ground to suddenly collapse. Simply put, it's a hole or depression formed when empty space (cavity) develops underground and the ground above it collapses.

Sinkholes can occur naturally, but in urban areas, they are mainly caused by human factors such as damaged aging water and sewer pipes, underground construction, and groundwater changes. They are urban disasters that can suddenly appear and cause significant damage to life and property.

💡 Why is this important?

• Sinkholes can occur without warning and cause casualties.
• They can seriously damage urban infrastructure such as roads and buildings.
• Their frequency is increasing with urbanization and aging infrastructure.

2️⃣ Types and Causes of Sinkholes

📕 Types and Characteristics of Sinkholes

• Sinkholes are classified into natural sinkholes and artificial sinkholes based on their causes. Sinkholes can be largely divided into two types. First, natural sinkholes occur in areas with soluble rocks such as limestone and gypsum due to dissolution by groundwater. They form when groundwater dissolves the rock to create a cavity, which grows until the ground above collapses. These are commonly seen in places like Florida in the United States and karst topography in China. Second, artificial sinkholes are ground collapses caused by human activities. They mainly occur in urban areas, with damaged water and sewer pipes, underground construction, and excessive groundwater extraction being the primary causes. Most sinkholes in Korea are of this artificial type. Generally, natural sinkholes are larger and form slowly, while artificial sinkholes tend to be smaller but occur suddenly.

• Sinkholes show various characteristics depending on their size and formation speed. Sinkholes exhibit different characteristics based on size and formation method. First, there is classification by size. Small sinkholes (diameter less than 2m) are minor depressions that occur on sidewalks or road surfaces, causing relatively little damage. Medium sinkholes (diameter 2-10m) are large enough to swallow vehicles or structures, causing considerable property damage. Large sinkholes (diameter over 10m) are serious disasters that can collapse entire buildings or road sections. Second, there are characteristics based on formation speed. Gradual sinkholes form as the ground slowly subsides over a long period, with cracks or subsidence signs appearing beforehand. Sudden sinkholes occur without warning, giving no time to respond and causing greater damage. Third, there are distinctions based on external exposure. Surface sinkholes are depressions that are immediately visible on the surface and can be identified visually. Hidden sinkholes are states where only underground cavities have formed without surface manifestation, making them more dangerous due to difficulty in detection.

📕 Main Causes of Urban Sinkholes

• Damaged aging water and sewer pipes are the most common cause of urban sinkholes. The most common cause of sinkholes in urban areas is damage to aging water and sewer pipes. First, looking at the aging and damage process of water and sewer pipes, most cities have complex underground water and sewer systems. Over time, these pipes deteriorate due to corrosion, cracks, and joint displacements. Pipes installed over 30 years ago have a high risk of leakage. Second, examining the soil loss mechanism around pipes, when water leaks from damaged pipes, it gradually washes away the surrounding soil. With sewer pipes, soil enters the pipe, and with water pipes, surrounding soil is washed away. Third, in the cavity formation and collapse process, continuous soil loss creates a cavity around the pipe, which gradually expands upward. Eventually, when the upper ground can no longer support the cavity, it suddenly collapses, creating a sinkhole. Fourth, regarding the relationship with road characteristics, roads continuously subjected to vehicle weight are more vulnerable. The possibility of occurrence is particularly high in areas with frequent vehicle stops, such as bus stops and traffic signal wait areas.

• Underground construction and groundwater changes are also major causes. Besides aging water and sewer pipes, various factors influence the occurrence of urban sinkholes. First, there's the impact of underground construction. Subway, underground shopping mall, and large building basement constructions can disturb the surrounding ground. Particularly, groundwater discharge or improper water cutoff during excavation can reduce stability of the surrounding ground. Second, there's the influence of groundwater level changes. Excessive groundwater extraction or blockage of groundwater inflow paths causes changes in groundwater flow. When the groundwater level drops rapidly, hydrostatic pressure between soil particles decreases, potentially causing ground subsidence. Third, there's the issue of interference between underground utilities. Various underground utilities such as electricity, gas, and communications can interfere with and damage each other, or the ground can be disturbed during installation. This problem is more serious in older cities where accurate underground utility maps may not exist. Fourth, there's the relationship with ground characteristics. Areas with unstable ground itself, such as landfills, soft ground, or fill layers, have a higher possibility of sinkhole occurrence. In these areas, ground stability can easily collapse with slight disturbance.

Signs and Warning Signals of Sinkhole Formation

1. Road surface cracks or depressions: Circular or radial cracks, small depressions
2. Pavement discoloration: Circular or oval discolored areas on asphalt surfaces
3. Water pooling: Water pooling in specific areas even when it hasn't rained
4. Ground subsidence: Buildings or structures tilting, cracks in walls or floors
5. Drainage problems: Drainage becoming slower than usual or backflow
6. Sound changes: Hollow or resonating sounds when walking in the area
7. Vegetation changes: Plants in specific areas dying or changing color
8. Groundwater changes: Sudden water level changes in wells or groundwater facilities
9. Muddy water near water sources: Unusually muddy water coming from wells or water pipes
10. Sink or toilet drainage issues: Strange sounds or drainage problems in household pipes

3️⃣ Impacts and Response Measures for Sinkholes

✅ Social Impacts of Sinkholes

• Sinkholes cause direct damage to life and property. Sinkhole occurrences cause serious damage in various aspects. First, there's human casualties. People can fall into or be buried in sinkholes that occur without warning, potentially resulting in death or serious injury. Pedestrians or vehicle drivers are at great risk especially when sinkholes occur on roads or sidewalks. Second, there's property damage. Vehicles, buildings, roads, water and sewer facilities can be damaged or collapse due to sinkholes. In some cases of large sinkholes, entire buildings may collapse. Third, there's infrastructure damage. When transportation infrastructure such as roads, railways, and bridges is damaged, it leads to traffic congestion and logistics disruptions, affecting the regional economy. When lifelines such as water and sewage, gas, and electricity are cut off, it directly inconveniences citizens' lives. Fourth, there are restoration costs. Significant costs are incurred for ground stabilization, facility restoration, and damage compensation after a sinkhole occurs. Particularly for large sinkholes or those near important facilities, restoration costs can amount to tens of billions of won.

• Sinkholes also have psychological and economic impacts on communities. Besides direct physical damage, sinkholes have various social impacts. First, they cause psychological anxiety. Residents in areas where sinkholes have occurred experience anxiety and fear about the possibility of additional occurrences. This anxiety can persist for a long time, especially in areas where large sinkholes have occurred. Second, they cause property value decline. Areas where sinkholes have occurred or designated as risk areas experience property value decline and insurance premium increases, resulting in economic damage. Third, there's damage to regional image. When an image forms of an area prone to sinkholes, it can negatively affect tourism, investment, and population inflow. Fourth, distrust in administrative agencies increases. If appropriate responses and recurrence prevention measures are inadequate after a sinkhole occurs, citizens' distrust in administrative agencies may grow. Due to these complex influences, sinkholes are recognized as social issues that affect the entire community beyond simple physical disasters.

✅ Sinkhole Prevention and Response Measures

• Efforts to prevent sinkholes are being made from various angles. Various technical and institutional efforts are underway to prevent sinkholes. First, management of aging infrastructure is important. Regular inspection of underground facilities such as water and sewer pipes and replacement of aging facilities is the most basic preventive measure. It's especially important to prioritize the replacement of pipes that are over 30 years old. Second, an integrated underground space management system needs to be established. The exact locations and conditions of underground utilities should be mapped digitally, and this should be referenced during underground construction to prevent interference. Third, ground investigation and monitoring are important. It's necessary to use non-destructive testing technologies such as ground-penetrating radar (GPR) and electrical resistivity surveys to detect and manage underground cavities early. Fourth, groundwater management is necessary. Groundwater flow and levels should be continuously monitored, and excessive extraction should be limited to maintain ground stability. Fifth, institutional management is important. Institutional measures such as strengthening safety regulations for underground construction, mandating ground stability assessments, and creating sinkhole risk maps need to be established.

• Prompt and systematic response is important when sinkholes occur. When a sinkhole occurs, damage should be minimized through prompt and effective response. First, initial response is important. Immediately control access and evacuate the surrounding area when a sinkhole is discovered, and assess the possibility of further expansion. Particularly, the safety of surrounding buildings, roads, and facilities should be promptly checked. Second, cause investigation is necessary. The exact cause of the sinkhole should be identified through ground investigation, underground facility inspection, and groundwater condition checks. This is essential for determining appropriate restoration methods and preventing recurrence. Third, restoration work is important. Work such as filling cavities, reinforcing the ground, and repairing damaged facilities should be systematically carried out. The stability of the surrounding ground should also be secured during the restoration process. Fourth, recurrence prevention measures need to be established. Based on cause analysis, prevention measures such as checking similar areas, removing risk factors, and establishing monitoring systems should be implemented. Fifth, resident communication is important. Information about the cause of the sinkhole, restoration plans, and safety measures should be transparently provided to residents, and communication should be maintained to alleviate anxiety.

4️⃣ Related Terminology

🔎 Ground Subsidence

• Ground subsidence is a phenomenon where the ground surface gradually sinks.
• Ground subsidence is a phenomenon where the surface gradually sinks, characterized by slow progression rather than sudden collapse unlike sinkholes. Ground subsidence can occur due to various causes: first, there's lowering of groundwater level due to excessive groundwater extraction. When groundwater is removed, hydrostatic pressure between soil particles decreases, compressing the ground. Second, there's cavity formation due to underground mining. Spaces created by resource development such as mines and coal mining gradually collapse over time, causing surface subsidence. Third, there's the consolidation phenomenon of soft ground. When loads such as buildings are placed on soft ground like clay layers, the ground compresses and subsides over a long period. Fourth, external factors such as earthquakes and vibrations also have an influence. Ground subsidence causes problems such as building tilting, road cracks, and underground facility damage, and in severe cases, it can develop into sinkholes requiring attention. For managing ground subsidence, regular ground level measurements, groundwater level monitoring, and observation of building inclination are important.

🔎 Underground Cavity

• An underground cavity is an empty space formed underground, the precursor stage of a sinkhole.
• An underground cavity is an empty space formed below the surface, which can be considered the stage before a sinkhole occurs. Underground cavities can form due to various causes: first, soil loss due to water and sewer pipe leakage is the most common cause. When water leaks from damaged pipes, it washes away surrounding soil, forming a space. Second, erosion by groundwater is also an important cause. Spaces form as groundwater dissolves certain materials (limestone, gypsum, etc.) or moves soil. Third, poor construction around underground structures can also be a cause. Insufficient backfilling or compaction during construction of subways, tunnels, underground parking lots, etc., can lead to cavity formation. Underground cavities are difficult to visually confirm and are detected using special equipment such as ground-penetrating radar (GPR) and electrical resistivity surveys. Discovered cavities are treated by injecting cement mixtures using grouting methods. While underground cavities themselves may have few problems, if left untreated, they can gradually expand and eventually develop into sinkholes, making early detection and treatment important.

🔎 GPR (Ground Penetrating Radar)

• GPR is equipment that uses electromagnetic waves to detect underground conditions.
• Ground Penetrating Radar (GPR) is a non-destructive testing equipment that detects underground conditions by analyzing signals reflected back after emitting electromagnetic waves underground. It is widely used for detecting underground cavities to prevent sinkholes. The operating principle of GPR is as follows: first, electromagnetic waves of a specific frequency are emitted underground from an antenna. Second, electromagnetic waves are reflected according to differences in electrical properties (dielectric constant differences) of underground materials. Third, the underground structure is analyzed by measuring the arrival time and intensity of the reflected signals. The main features of GPR include: first, non-destructive testing is possible. Underground conditions can be checked without damaging the surface. Second, it has good mobility. A wide area can be quickly surveyed by mounting on vehicles or pushing manually. Third, real-time data confirmation is possible. Scan results can be immediately checked on-site, allowing for prompt judgment. GPR is used to detect various underground elements including not only underground cavities but also buried pipes, cables, cultural properties, and geological structures. However, it has limitations in that detection performance varies depending on soil conditions (clay, moisture), and accuracy decreases with depth.

5️⃣ Frequently Asked Questions (FAQ)

Q: What should I do when I notice signs that might indicate a sinkhole?

A: If you notice signs of a possible sinkhole, it's best to respond as follows. First, immediately evacuate to a safe distance. Move away immediately from areas showing abnormal signs such as ground subsidence or cracks, and inform others not to approach. Second, report to relevant authorities. If discovered on roads or public places, report to the local government's safety management department, road management department, or call 119. Providing a detailed explanation of the exact location and condition allows for faster response. Third, take photos or videos. Recording the condition from a safe distance can help with expert assessment. Fourth, if discovered on private property, seek advice from an architect or ground expert. Structural safety assessment may be necessary, especially if found near buildings. Fifth, refrain from temporary measures. Temporary measures such as filling sunken areas with cement or soil can make it difficult to identify the cause and hide bigger problems, so it's best to maintain the status quo until experts arrive. Sixth, also check surrounding facilities. Ground problems may be related to nearby water and sewer pipes, gas pipes, etc., so also check and report abnormal signs such as leaks or gas smells.

Q: How do urban sinkholes differ from naturally occurring sinkholes?

A: Urban sinkholes and naturally occurring sinkholes differ in several aspects. First, they have different causes. Urban sinkholes are mainly caused by human activities such as damaged aging water and sewer pipes, underground construction, and underground facility interference. In contrast, naturally occurring sinkholes are natural phenomena caused by soluble rocks like limestone and gypsum dissolving in groundwater. Second, they have different geological characteristics. Naturally occurring sinkholes mainly occur in specific geology (karst topography) and have distinct regional characteristics. Urban sinkholes are more influenced by infrastructure conditions and management levels than geology. Third, they have different predictability. Naturally occurring sinkholes can be somewhat predicted through geological studies of risk areas. Urban sinkholes are more difficult to predict if the conditions of underground facilities are not properly understood. Fourth, they have different sizes and shapes. Naturally occurring sinkholes tend to be larger, deeper, and more circular. Urban sinkholes are relatively smaller and often have irregular shapes. Fifth, they have different formation speeds. Naturally occurring sinkholes often develop slowly over hundreds of years, while urban sinkholes tend to occur suddenly in a relatively short time.

Q: Is insurance compensation possible for sinkholes?

A: Insurance compensation for sinkhole damage varies depending on the type of insurance and contract terms. First, regarding comprehensive home insurance (fire insurance), typical domestic home insurance policies often do not explicitly cover sinkhole damage. However, some premium products may cover it under 'ground subsidence' or 'natural disaster' categories, so it's important to check your contract terms. Second, for auto insurance, if you have comprehensive coverage (own damage insurance), vehicle damage due to sinkholes may be compensated under the 'own vehicle damage' category. However, interpretation may vary by insurance company, so consultation with your insurer is necessary when an incident occurs. Third, if the sinkhole is caused by construction or facility defects, compensation may be available through the liability insurance of the construction company or facility management entity. In this case, determining the cause of the sinkhole and liability is important. Fourth, personal injury insurance may cover medical expenses for injuries caused by sinkhole accidents. Fifth, recently, some insurance companies have been developing special clauses or products that explicitly cover sinkhole damage, so if you live in an area with sinkhole concerns, these products may be worth considering. In any case, it's important to secure sufficient evidence such as site photos and damage records when damage occurs.

Q: How can I tell if my neighborhood is safe from sinkholes?

A: There are several ways to assess your neighborhood's sinkhole safety. First, check the local geological characteristics. Limestone areas or karst topography have a higher possibility of natural sinkhole occurrence. Geological maps or ground information can be checked through materials provided by the National Geographic Information Institute or Korea Institute of Geoscience and Mineral Resources. Second, determine the age of underground facilities. You can inquire about when water and sewer pipes were installed and their condition from the local government's water or sewage department. Areas with many aging pipes over 30 years old may have relatively higher risk. Third, investigate the history of past ground subsidence or sinkhole occurrences. Past cases in the area can be confirmed through the local government's safety management department or local news searches. Fourth, check for nearby large-scale underground construction. Construction such as subways or large building basements can affect ground stability. Fifth, refer to regional safety indices or disaster safety maps. Safety information provided by the Ministry of the Interior and Safety and local governments may include content about ground safety. Sixth, seek expert opinions. If you're planning real estate purchases or construction, it's good to get advice from architects or geotechnical engineers. Especially if there are suspicious symptoms (ground cracks, building tilting, road collapse, etc.), a detailed diagnosis by experts is needed.