Late on Thursday evening, Spanish cavers in Madrid received an urgent message that one of their most well-known colleagues, 46-year-old Cecilio López, had suffered a fall from a height of five metres inside a cave in north-western Peru and was badly injured 400 metres underground.

Mr. López, an experienced potholer who had participated in several prior archaeological expeditions to Peru's Intimachay chasm, has broken several vertebrae and is unable to climb out himself.

Spanish spelunkers immediately began to coordinate a private international rescue mission to help Mr. López, who has...