After a Cave Turns Deadly, Scientists Seek Answers

Raul Perez Lopez peers into the darkness of CJ-3, a cave that's mysteriously losing its oxygen. (Credit: Antonio Marcos Nuez) A deadly mystery lingers in a cave in northern Spain. A sign at the entrance warns visitors not to enter. For decades, speleologists have trained inside CJ-3, a 164-foot-deep cave in Cañon del Río Lobos Natural Park in the Soria province. But in 2014, visitors to the cave experienced something new at the bottom: they nearly suffocated, and one person fainted. The oxygen levels had suddenly, and inexplicably, dropped. The unusual incident prompted park officials to contact geologist Raul Perez Lopez of the Geological and Mining Institute in Madrid, Spain. Shortly after the first report, daredevil Perez dove into action. Perez along with two firefighters who specialize in mountain rescues went to investigate CJ-3. In the most dangerous move of his 20-year career, Perez, with the help of a firefighter, lowered himself by rope to the bottom of the deadly cave. “Upon arriving to the bottom, our gas detector started to beep because there was a lack of oxygen,” said Antonio Marcos Nuez, a geologist and firefighter who entered the cave with Perez to ensure its safety. “I’ve been entering caves for more than 25 years, and such a low oxygen percentage is a very unique situation.”