Resource: Mount Pinatubo: The Aftermath of a Volcanic Eruption

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Mt. Pinatubo's 500-year dormancy ended in early April 1991. For weeks, the volcano sent warning puffs of gas and ash into the air above the island of Luzon in the Philippines. Scientists monitoring the volcano's activity, including the seismic rumblings deep within it, concluded that a powerful eruption was imminent. This prediction prompted the evacuation of 50,000 people who lived on or near the volcano's slopes, a measure that undoubtedly saved thousands of lives. Despite the warning signs and precautions, however, the power Pinatubo unleashed when it exploded on June 15th, 1991, surprised many people. And yet, the eruption itself was only a precursor to the greater devastation still to come.

Pinatubo's 1991 eruption stands as the second-most-powerful volcanic event on Earth in more than a century. The blast created immense avalanches of searing hot gas, ash, and rock, called pyroclastic flows, which roared down the volcano's slopes. Approximately 500 people died as a result. In all, the eruption scattered four to seven cubic kilometers (140 to 250 cubic feet) of ash and rock over the surrounding area, burying some locations under 200 meters (650 feet) or more of debris. This massive accumulation of unstable material set the stage for the next phase of destruction.

Within hours after Pinatubo's eruption, a typhoon began dumping heavy rains on the area. The rainwater mixed with the loose volcanic material on the volcano's slopes to form a dense, viscous mud with the consistency of wet cement and cause mudflows, called lahars, to race down Pinatubo's slopes. Ever since, during periods of intense rain, more lahars have periodically carried boulders, homes, vehicles, and bridges down the slopes with them, destroying or burying nearly everything in their path. In the first few years after the 1991 eruption, lahars deposited more than three cubic kilometers — about 300 million dump-truck loads — of debris on the lowlands surrounding the volcano. Since 1991, lahars have destroyed the homes of 100,000 people, and nearly 15 years later they continue to threaten at least 100,000 more.

Because lahars continue to flow down Pinatubo's slopes, early warning is critical. Scientists use remote sensing tools to monitor rainfall and ground vibration in the hope that they will be able to warn down-slope communities of an imminent or active lahar.

To learn more about the eruption of Mt. Pinatubo, check out Mount Pinatubo: Predicting a Volcanic Eruption.

To learn more about the risks volcanoes pose, check out Volcanic Eruptions and Hazards.

To learn more about volcanoes and how they form, check out Volcanism, Plate Tectonics: The Hawaiian Archipelago, and Tectonic Plates, Earthquakes, and Volcanoes.

Print Questions for Discussion

• Describe some of the phenomena that occur in the aftermath of a volcanic eruption.
• What impacts do these phenomena have on humans?
• What effects of a volcano on people and the environment are a surprise to you? Explain.
• How can the communities surrounding Mt. Pinatubo protect themselves from the effects of future eruptions?