For weeks our attention was gripped by the story of the Thai soccer team trapped within the Tham Luang caves in Thailand, and the international rescue mission that has seen them safely evacuated.
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The incident seems almost certain to make the caves a new “must see” tourist destination in Thailand. But how do these sorts of caves form, and how did these kids become trapped so quickly?
The Tham Luang cave system is a network of around 10km of tunnels, under the Doi Nang Non mountain range.
Like much of Thailand, the mountain is made mostly of limestone. It’s this limestone, when combined with water, which has allowed for the formation of this massive cave system.
Limestone is a type of sedimentary rock that forms from the skeletal remains of marine organisms. Over millions of years layers of shells and mud form and are slowly compressed.
The result is soft, chalky limestone, which is composed mainly of calcium carbonate.
The way these caves form is also the reason that the Thai rescue was so difficult.
When limestone meets rainwater a simple chemical reaction takes place. This is because rainwater is naturally slightly acidic. As raindrops fall they interact with carbon dioxide gas in the air, forming carbonic acid.
When calcium carbonate is mixed with carbonic acid the calcium carbonate is broken down to form calcium and bicarbonate.
In the context of caves, what this means is that when limestone is exposed to slightly acidic rainwater, the limestone dissolves away.
The opposite reaction can also occur, with calcium carbonate precipitating out of solution. This causes the stalagmites and stalactites that caves are famous for.
These reactions have been taking place in the mountains of Thailand over millions of years. Rainwater has been ever so slowly eroding Doi Nang Non, forming channels and tunnels as it slowly seeps through the mountain.
The way these caves form is also the reason that the Thai rescue was so difficult. Although the process can result in large caverns, it often creates narrow channels as rainwater moves through crevices in rock. These channels were easy enough for the boys to squeeze through in the dry – but once underwater they were a hazardous obstacle for even experienced divers.
The process of cave formation is also what makes these caves so dangerous in the wet season. The cracks and crevices formed in the mountain mean that rain water can quickly flow in and flood the cave system, as the Wild Boars team soon found out.
Dr Mary McMillan is an associate lecturer at the University of New England’s School of Science and Technology.
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