The trail networks crisscrossing El Malpais National Monument are often marked with lava cairns, rocky reminders of the arid New Mexican park’s previously volcanic life. Below the monument’s striking surface are numerous corridors—close to 500 lava tubes, formed when searing channels of liquid rock made trails through the land.Recently, one of those tubes gave up a secret, tucked away in ice nearly 50 feet underground, a mile and a half above sea level. The mystery was how ancestral Puebloans survived droughts, and it was solved in an ice core about…
