The Warning Systems

Modern volcano observatories monitor active volcanoes 24/7 using networks of seismometers, GPS stations, gas analyzers, and satellite imagery. Before most eruptions, there are detectable warning signs: increased earthquake swarms, ground swelling, rising sulfur dioxide emissions, and changes in groundwater chemistry.

The Philippines' PHIVOLCS issued a warning before Mount Pinatubo's 1991 eruption that led to the evacuation of over 60,000 people, saving tens of thousands of lives. In contrast, Colombia's Nevado del Ruiz erupted in 1985 and killed about 23,000 people in the town of Armero, despite scientists' warnings.