Almost like church bells or a clock tower, a town in the western highlands of Guatemala has been able to practically tell the time by the regular eruptions of a local volcano. In the town of Quetzaltenango, volcanic eruptions have occurred so frequently that they have nearly marked every passing hour of every day for 94 years.

The source: Santiaguito, one of the world’s most active lava-dome complexes, which is situated at the base of the stratovolcano Santa Maria. The complex formed about 20 years after a massive explosion in 1902.

“[Since then], almost continuous minor explosions have accompanied the growth of the Santiaguito,” says Stephanie Grocke, a National Geographic Explorer and volcanologist. “There has not been an extensive period of