On January 20 - 23, 2025, Lang Son Provincial Agency for Investment, Trade and Tourism Promotion in coordination with Viet Nam Expeditions Joint Stock Company and related agencies and units organized a survey of Lang Son Geopark Sinkhole in Mong An Commune, Binh Gia District, Lang Son province, Viet Nam. 

Tham Lum Sinkhole has GPS location: 21°58'45.7"N 106°19'46.7"E. Tham Lum Sinkhole is located in the middle of a cliff at an altitude of about 500m above sea level. To reach the sinkhole, the expedition team had to walk about 1.5km through the local Anise Forest and also about 1.5km National Highway 279 in the direction of Dang Mo Waterfall.

The sinkhole is located at an altitude of 500 m above sea level and was formed by an underground river flowing through a cave corridor in the limestone mountain and eroding the bedrock, causing the bedrock to weaken and the cave ceiling to thin, leading to a collapse forming a giant inverted funnel-shaped sinkhole, the mouth of the sinkhole is smaller but the bottom of the sinkhole which is gradually wider. According to a preliminary survey, Tham Lum Sinkhole has many adjacent caves and sinkholes, underground rivers within a radius of 3km to 5km. This is a typical geological feature of a massive cave network. To determine accurately, it is necessary to survey and map the entire area in detail.

The terrain of Tham Lum Sinkhole is a vertical sinkhole due to the cave ceiling collapsing, so to approach the sinkhole, you need to use ropes and safety equipment. The point where you can drop down the rope to explore is 60m deep and the deeper you go down the bottom of the sinkhole, you will discover two branches of the Underground Cave developing in the Southeast - Northwest direction. These two branches of the cave develop in the direction of the underground river, so it is very likely that a cave - underground river system will appear connecting the sinkholes and caves in the area as shown on the map.

In the bottom of the sinkhole is a primeval forest with a diverse flora system under the sinkhole; there are gaps with great potential for developing camping tourism. However, the camping site needs to be specifically planned so as not to affect the landscape and impact the pristine forest ecosystem.

The cave system in the sinkhole is a pristine cave system, untouched by humans with many beautiful stalactites, with great potential for adventure tourism and scientific research.

Deep below the cave, after continuing to descend 100m, an underground river appears. This is a very useful basis for further exploration and survey to determine the entire cave and sinkhole system.

Evaluation of results: Tham Lum Sinkhole is an important and extremely impressive discovery in Lang Son Geopark, affirming the uniqueness and diversity of terrain and geomorphology in the Geopark, and there, it is possible to develop more types of sinkhole exploration tours. This is also a sinkhole with a high diversity of forest systems in the sinkhole, as well as caves and underground rivers. There is high potential to create products for sinkhole exploration tours, camping in the sinkhole, exploring caves in the sinkhole as well as exploring underground rivers, etc. However, Tham Lum Sinkhole has a lot of potential but the terrain and the system of primary forests and caves in the sinkhole are very vulnerable and potentially dangerous. Therefore, the development of a tourism product needs to be carefully researched to ensure the safety of visitors and to protect and preserve the biodiversity and integrity of the sinkhole. In order to have more basis for developing sinkhole exploration tours, Vietnam Expeditions Joint Stock Company proposes to organize tours and trial experiences under the supervision of safety experts and adventure experts, to collect customer experiences as well as have objective assessments before completing the product to apply for an official license to put the tourism product commercial exploitation.

In the coming time, Lang Son Provincial Agency for Investment, Trade and Tourism Promotion will continue to coordinate with experts, local authorities, and Vietnam Expeditions Joint Stock Company to conduct a thorough survey to propose a comprehensive solution for landscape, infrastructure and environmental sanitation with the aim of building the Sinkhole a unique and attractive tourism product of Binh Gia in particular and of Lang Son Geopark (Lang Son province, Viet Nam) in general.

Pham Huong