In just two months, 11 sinkholes have occurred in Quỳ Hợp District. According to scientists, dry weather and lowered groundwater levels have exerted pressure on the geological layers.
For several months, residents of Châu Hồng and Liên Hợp communes in Quỳ Hợp District, Nghệ An Province, have been living in constant fear due to the continuous appearance of “death holes.” Many of these holes are 2-7 meters wide and 2-2.5 meters deep. The sinkhole phenomenon coincided with a time when hundreds of household wells in Châu Hồng commune ran dry.
The “death hole” in Mr. Thắm’s yard, Châu Hồng commune, on October 26. (Photo: Phương Linh)
The authorities in Nghệ An Province have established several survey teams, but as of now, the cause remains unidentified.
Explaining the phenomenon, Associate Professor Dr. Trần Tân Văn from the Institute of Geological Sciences and Mineral Resources stated that Quỳ Hợp is a limestone mountainous area with many underground karst caves. When faced with specific weather conditions such as prolonged heavy rain or dry spells, the lowering of water levels can lead to sinkholes.
“This sinkhole occurrence in Quỳ Hợp is attributed to dry weather, rapid decreases in groundwater and river water levels increase the load on the ceilings of caves, leading to sinkholes“, Dr. Tân explained, noting that this is not unusual. The groundwater here acts as a “support” for areas with underground karst caves. When water is no longer present, these caves collapse, resulting in “death holes.”
“Water is always the “culprit” in cases of ground subsidence and sinkholes, creating voids beneath the surface. This is also true for the cases of death holes in major cities built on weak ground, such as Ho Chi Minh City and Hanoi”, he added.
In limestone regions, there are places where the rock is submerged beneath a layer of soil. The special characteristics of limestone (and some other types of rock containing lime or salt) are easily dissolved by flowing water, creating caves. The dissolution process, combined with mechanical collapse, forms these cavities, collectively known as the karst process. Karst sinkholes are numerous in limestone areas, often forming a series of round sinkholes with diameters and depths ranging from a few meters to several tens or even hundreds of meters, above underground rivers.
Dr. Tân warned that areas where “death holes” have previously appeared are highly likely to experience further sinkholes in the future. While there are many technologies that can assess the scale of these occurrences, there is currently no technology that can effectively remediate sinkholes, even filling them with concrete or gravel, as they will be washed away shortly after. Therefore, residents should urge local authorities to facilitate their relocation to safer areas.
“If you live near limestone mountains, there is a strong possibility that there are underground limestone formations and cavities below, which can easily collapse during heavy rains or dry spells. This is especially true in areas near rivers, mining operations, or groundwater extraction, where rapid lowering of water levels can cause collapses”, Dr. Tân noted.
Currently, Vietnam has not conducted a comprehensive survey of sinkhole phenomena in caves. The Institute of Geological Sciences and Mineral Resources is implementing a survey project in several provinces such as Quảng Ninh, Cao Bằng, Lạng Sơn, and Hà Giang… To create a complete warning map, Dr. Tân believes that surveys are needed in all limestone mountainous regions, which account for approximately 40% of the total area of Northern Vietnam.
He recommended that the government promptly plan investigations and demarcate areas to relocate residents living in high-risk sinkhole zones to geologically safe regions.
