Why Hydrogeology Plays Such An Important Role In The Thailand Cave Rescue Operations

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June 23 a group of twelve boys together with her soccer coach entered the “Great Cave of the Sleeping Lady” (Tham Luang Nang Non), located in the Chiang Rai province in northern Thailand. In 1988 a French team of cave explorers mapped for the first time the cave, some years later a British team discovered a passage to another cave, but still, the exact geometry of the cave system is poorly known. Tham Luang cave is at least six miles long, forming a network of caverns and narrow passageways in the Doi Nang Non mountain range.

Apparently, it was not the first time the now trapped group explored the cave. Authorities found some of the group’s belongings at the entrance of the cave after parents reported the kids missing. After recent rainfalls (June-July marks the beginning of the monsoon season in the region) parts of the cave flooded and authorities feared that the group either drowned or was trapped inside the cave.

D. Bressan

Schematic cross section and map (not to scale) of the Tham Luang cave.

Water plays an important role in the formation of caves, but it is also by far the most dangerous element when exploring wild cave systems. According to the geological map of Thailand the Doi Nang Non mountain range is composed of a succession of sandstone, limestone, shale and chert. Limestone is a sedimentary rock, vulnerable to tectonic deformation and erosion by water. Water enters the mountain following superficial cracks and faults. As limestone is dissolved by this groundwater, a three-dimensional network of caverns and conduits forms over time. Such karst systems act like a natural sponge inside the mountain. Some days of good weather and the cave appears completely dry. In fact, during the dry season (September-June) Tham Luang cave can be easily reached on foot (even if it is forbidden to enter). As soon as the cave’s entrance flooded after a flash flood, the group was forced to venture deeper inside the cave. A strong rainstorm is sufficient to flood also the inner network as the water, flowing in open cracks and conduits, can travel up to 1,000 ft through the porous limestone-rock in less than one hour.

July 2 all the members of the soccer team were found alive inside the partially flooded cave by a British diver. The boys were huddled together on the side of a steep rock in a dry section of the cave. More than 1,000 rescuers are working to save the group at the moment. The oxygen concentration in the closed cave environment is dangerously low (just 15% compared to 20-21% in open space) and new rainstorms are expected in the coming days.

Rescue teams searched for alternative ways inside the Doi Nang Non mountain, as cave systems in karst areas often have multiple entrances. One team traveled some 900 ft down a shaft on Thursday until they reached a dead end. Drilling teams drilled more than 100 shafts through the mountain. Some of the shafts are as deep as 1,300 ft, but they still cannot find their location yet, as there are no exact maps the shafts missed the cave.

Technicians used powerful pumps and also diverted some superficial streams to lower the water level inside the cave. The first mile of the cave now is dry and can be accessed with heavy equipment. Authorities decided to risk today a rescue attempt, taking advantage of the good weather and hoping to be successful before the next rainstorms will raise again the water levels inside the cave. The boys will be accompanied and guided by two experienced divers, as they need to dive through the flooded sections. An extremely risky operation as the death of one of the rescuers, drowned in one of the flooded sections, on July 6 shows. The flooded passages are short but very narrow, less than three ft in diameter. As the water flows under pressure into the cave dangerous currents form there. The currents also transport sediments from the surface into the cave and in the mud-clogged water it is easy to lose orientation.

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