22. The “Minor” Eruption That Killed Tens of Thousands
Colombia’s Nevado del Ruiz, located about 75 miles northwest of Bogota, is a typical stratovolcano. Those are made of multiple layers, or strata, of hardened lava, pumice (volcanic debris), tephra (dust), and ash. What is atypical about Nevado del Ruiz is that it is located by a river valley, which makes its eruptions produce flows known as “lahars”. Those are mud flows made of a slurry of volcanic debris, rocks, and water.
The lahar flows are particularly powerful in Nevado del Rio’s case because it is located high up in the Andes, and its top is covered with a glacier. That is, a lot of frozen water just waiting to come down in an eruption as an avalanche and flow of snow, melted water, and debris. On November 13th, 1985, after lying dormant for seven decades, Nevado del Ruiz awoke from its slumber and became active. It was a minor eruption, far as volcanoes go, but it produced a massive and massively devastating lahar. Tens of thousands died in the ensuing disaster.
