Summary
Highlights
In 1991, Mount Pinatubo, previously considered a mere mountain, began showing signs of activity. Located in the Philippines, part of the Pacific's 'Ring of Fire,' this volcano was not monitored, and its potential for a massive, explosive eruption was initially underestimated by local authorities and residents.
The Philippine Institute of Volcanology and Seismology (PHIVOLCS) was alerted to strange explosions and tremors by local nuns and indigenous tribes. Faced with a complete lack of historical data for Pinatubo, they requested assistance from the United States Geological Survey (USGS).
Scientists established a temporary base to monitor Pinatubo. Through carbon dating of pyroclastic deposits, they discovered a history of massive eruptions, with a Volcanic Explosivity Index (VEI) of 6, indicating a catastrophic potential. The immense magmatic chamber beneath the mountain concerned experts, as an eruption could impact over 500,000 people and trigger a 'volcanic winter' globally.
To predict the eruption, scientists monitored sulfur dioxide emissions and seismic activity. A significant increase in SO2, reaching 5,000 tons per day, and continuous seismic tremors indicated magma rising to the surface. An evacuation plan was developed, but faced skepticism and ignorance from local populations.
Scientists used educational videos of volcanic eruptions, including footage from famed volcanologists Katia and Maurice Krafft, to convince residents of the danger. The tragic death of the Kraffts in a pyroclastic flow in Japan shortly before Pinatubo's main eruption reinforced the message. Despite a temporary decrease in activity that caused doubt, renewed seismic activity and the visible formation of a lava dome confirmed the imminent threat, prompting the evacuation of 300,000 people, including US military personnel.
On June 12, 1991, Pinatubo began its eruption, initially with an 'umbrella-shaped' cloud. After a brief pause, the main eruption occurred on June 15 at 13:41, with magma rapidly ascending, causing an explosive column to reach 40 km in altitude. This coincided with a tropical typhoon, creating an apocalyptic scene of ash, rain, pyroclastic flows, and deadly lahars.
After 9 hours, the volcano's summit collapsed, forming a caldera and signaling the end of the main eruption. The landscape was devastated, covered in thick ash, with pyroclastic deposits exceeding 200 meters in some areas. The eruption directly caused 350 deaths, mostly from collapsing roofs, and subsequent lahars raised the total to 800. Globally, 20 million tons of sulfur dioxide in the stratosphere caused a 'volcanic winter,' lowering global temperatures by 0.5°C over three years. The event highlighted the importance of volcanology in safeguarding human lives.