Seventeen days after they went missing, a team of teenage footballers of a local club in northern Thailand were rescued in the evening of 10 July. Numbering 13, including the 25-year-old assistant coach, they lost their way inside a mammoth cave system known as Tham Luang under the Doi Nang Non mountain range which straddles Chiang Rai and Mae Sai districts of the country’s Chiang Rai province.

In an operation that brought together the best of the divers, cartographers and speleologists from around the world, all of the lost boys of the local football club known as Wild Boar and their coach were rescued. Even Elon Musk, the billionaire founder of SpaceX and Tesla had offered a helping hand. (His offer of a submersible was rejected after it was found that it is not suited for the rescue operation due to the contours of the cave.)

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Rescuers had made first contact with the kids and their coach about five kilometres deep inside the cave. They had taken refuge on an elevated ground which was at a depth of about 900 metres from the surface. Fighting against the threat of heavy rains that could have jeopardised the mission, the rescue team brought back the boys aged 11-17 and their coach out alive.

READ: Thai cave rescue ops ends in complete success, 12 boys and coach evacuated

But is it so difficult to rescue anyone from inside a cave? Many wondered why divers, that too from elite Navy Seals, were deployed for the rescue mission asking how water could enter and flood a cave system besides the obvious question on how the 13 ended up so deep inside. Here are some questions answered.

Where is the cave located and why is it called a system?

The cave system is located under the Doi Nang Non mountain range, which spreads itself over the Thailand-Myanmar border. The mountain is karstic, meaning that it was formed from the dissolution of soluble rocks such as limestone, dolomite, and gypsum.

The cave system, crisscrossing 10 km, is called Tham Luang (not to be confused with Tham Khao Luang, which is located in Phetchaburi region in the eastern part of the country). Being a cave system, Tham Luang has many smaller caves, chambers and antechambers accessible through a network of passages and tunnels.

It’s been super confusing for the past week so here it is, the official cave map from the govt: Entrance to Sam Yak junction-3km. (Entrance to Chamber 2 -800m, Ch2-Ch3 -700m, Ch3-junction -1.5 km) Junction to Pattaya Beach 1.5 km #Thailand #dpareporter #ThamLuang #ถ้ำหลวง pic.twitter.com/X1DOrvnt74

— Hathai Pia (@HathaiPia) July 1, 2018

Unlike the similar sounding Tham Khao Luang, Tham Luang is not a major international tourist attraction. Its location is quite far from the more urban regions of Thailand, all of which are located in the south, southeast and east of the country. However, Tham Luang is very popular among the locals, trekkers and avid cavers.

What was the team doing inside the cave?

Reports say that the boys and their coach went inside the caves to celebrate the birthday party of the oldest member of the Wild Boars team, who turned 17. They left their bikes at the entrance and entered the complex even though visitors are warned not to do so during the monsoon season.

The structure of the cave

On a normal day, the cave is easier to explore. The entrance is from the eastern side and leads to a T-intersection known as the Sam Yak Junction. To right of the junction leading north is the border of Myanmar. To the south, about 1.5 km through a series of winding, rising and downward sloping corridors, is the Pattaya Beach. Named after the world famous beach located in the southern part of Thailand, the ‘Beach’ in the cave is actually a huge cavern on a raised ground – the largest part of the cave.

The team was found farther down Pattaya Beach.

How did water enter the caves and get accumulated?

Most caves around the world have numerous openings on the top from where water can enter the system, and Tham Luang is not different. In the rainy season, the cave system, which is spread inside a mountain, gets flooded due to the accumulation of water in the lower chambers, tunnels and passages. Dripping stalactites create further problems for entry and exit of trekkers. Divers were brought in to navigate through the passages filled with water. So narrow were some passages that divers had to remove their oxygen tanks to make enough space to pass through.

Saman Kunan, a former Thai navy seal, diver asphyxiated to death while replenishing air tanks between two chambers. His death is the only fatality in the mission.

The extremely high risk to life is why visitors are warned against entering the cave system during monsoons. The boys and their coach entered the cave during the monsoon season. Heavy rains immediately after they entered the cave flooded the passages thus blocking their exit.