The discovery of the underground river is not accredited to a single person or expedition. Dean Worcester from the University of Michigan (1887) is the first person to have written about the river. Long before the work of Worcester, the local Batak people knew of the cave (and the river) but few ventured in as they believed an evil spirit had made the caves its home.
The national park that houses the river is located in the Saint Paul Mountain Range. The mountains have been formed from grey limestone. This limestone formation has been calculated to have formed between 16 and 20 million years ago.
The entrance of the cave is called the Daylight Hole. It is about 60 meters high and 100 meters wide. It only begins to narrow from 200 meters within the cave.
The Cabayugan River, as a small stream, disappears as it arrives at the limestone of the mountain. At this point, the river is only 30 meters above sea level and 6 km from the sea (as the crow flies). Until it meets with the sea, the river flows for 8.2 km underground and is about 8 meters deep.
According to the government of the Philippines, the Puerto Princesa Subterranean River has at least 11 different types of minerals. These are serrabrancaite, robertsite, janggunite, calcite, gypsum, apatite, variscite, strengite, manganite, rodocrosite, and pirolusite
This subterranean river was often referred to as the longest in the world until 2007 when an underground river was discovered in Mexico’s Yucatán Peninsula.
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