All Thirteen: The Incredible Cave Rescue of the Thai Boys' Soccer Team

Just what it sounds like, groundwater is water contained in soil and rocks underground. Understanding the groundwater situation at Tham Luang is essential to understanding why it flooded so quickly. As rain fell in Mae Sai in the days before June 23, 2018, the ground became saturated, or full of groundwater. However, the groundwater wasn’t visible to the boys; they walked through the cave on dry ground.

When a particularly intense rainstorm hit on the afternoon of June 23, the rainfall had nowhere to go—the ground was already saturated. This is why the Sam Yaek junction began to flood so quickly. Water came up from the ground as the amount of rainfall surpassed the ground’s ability to absorb the water. Thanet understood this phenomenon, which is why he chose to pump out groundwater from a connected cave in an effort to lower the groundwater from the bottom and make room for the falling rain to sink into the earth.

In cave diving, a guideline is a piece of rope that acts as a guide for divers to follow as they move through the tunnels and chambers of a cave. Since light from Earth’s surface isn’t visible in a cave, cave divers can easily become disoriented and lose track of which way they’re traveling. In addition, visibility underwater can be poor if the water is moving quickly or if silt is stirred up. A guideline provides a path that cave divers can follow and hold on to so that they have less chance of becoming lost or disoriented.

The Thai Navy SEALs didn’t have cave diving experience and therefore didn’t know that a guideline is critical for safety. They attempted to dive without first laying a guideline. The lack of a guideline and the intense water current made it impossible for them to enter the flooded passages of Tham Luang for several days. The cave diving specialists, Rick and John, refused to dive without a guideline and were unable to set one in place for several days because of the current.

Tham Luang is made of karst limestone. This type of rock is porous and full of holes, and therefore it commonly forms caves. Karst is formed when acidic rainwater dissolves the calcium carbonate in limestone. Over time, as water seeps into holes and cracks in a landscape, holes form, and eventually large chambers form, creating caves underground.