(CNN)Shift leader Luis Urzua checked the time.
It was about 1:40 p.m. He had just felt a rumble in the Earth, and over the clanging and clamoring of mining equipment, Urzua heard a noise.
Despite the unnerving rumble, he continued working at the San José Mine in Chile’s Atacama Desert. He and a group of men were working to extract gold and copper nearly a half-mile below ground in the 100-plus-year-old mine.
But five minutes later, Urzua felt the mountain rumble again, and he knew something was wrong.
“The mountain always gives you a warning. The mountain doesn’t collapse on its own. This is something we know as miners — there is always something,” said Urzua, who had been a miner for 31 years.