Volcano Expertise and Monitoring Save Lives--The Case of Mount Pinatubo, Philippines

By Chris Newhall, James W. Hendley II, and Peter H. Stauffer

On the morning of June 15, 1991, Mount Pinatubo in the Philippines exploded in the largest volcanic eruption on Earth in more than three-quarters of a century. The most powerful phase of this cataclysmic eruption lasted more than 10 hours, creating an enormous cloud of volcanic ash that rose as high as 22 miles into the air and grew to more than 300 miles across, turning day into night. Falling ash blanketed an area of thousands of square miles, and avalanches of hot ash called pyroclastic flows roared down the slopes of the volcano and filled deep valleys with deposits of ash as much as 600 feet thick.

Before the cataclysmic eruption, roughly one million people lived in the region around Mount Pinatubo, including about 30,000 American military personnel and their dependents at the two largest U.S. military bases in the Philippines--Clark Air Base and Subic Bay Naval Station. The slopes of the volcano and the adjacent hills and valleys were home to thousands of villagers. Despite the great number of people at risk, there were few casualties in the June 15 eruption. This was the result of intensive monitoring of Mount Pinatubo by scientists with the Philippine Institute of Volcanology and Seismology (PHIVOLCS) and the USGS.

The first recognized signs that Pinatubo was reawakening after a 500-year slumber were a series of small steam-blast explosions in early April 1991. Scientists from PHIVOLCS immediately began on-site monitoring and soon declared a 6-mile-radius danger zone around the volcano. They were joined in a few weeks by USGS scientists from the Volcano Disaster Assistance Program, a cooperative effort with the Office of Foreign Disaster Assistance of the U.S. Agency for International Development.

The USGS scientists brought with them specially designed, portable instruments, which the joint Philippine-American team used to quickly set up monitoring networks on and around Mount Pinatubo. The team also conducted intensive studies of the volcano's past eruptive history. When the data from these efforts indicated that a huge eruption of the volcano was imminent, the joint team issued urgent warnings. These timely forecasts enabled civil and military authorities to arrange the evacuation of people and aircraft and other equipment to safe areas before Mount Pinatubo exploded on June 15.

The USGS and PHIVOLCS estimate that their forecasts saved at least 5,000 lives and perhaps as many as 20,000. The people living in the lowlands around Mount Pinatubo were alerted to the impending eruption by the forecasts, and many fled to towns at safer distances from the volcano or took shelter in buildings with strong roofs. Additionally, more than 18,000 American servicemen and their dependents were evacuated from Clark Air Base prior to the June 15 eruption. In the eruption, thousands of weaker roofs, including some on Clark, collapsed under the weight of ash made wet by heavy rains, yet only about 250 lowland residents were killed. Of the 20,000 indigenous Aeta highlanders who lived on the slopes of Mount Pinatubo, all but about 120 were safely evacuated before the eruption completely devastated their villages.

In addition to the many lives saved, property worth hundreds of millions of dollars was protected from damage or destruction in the eruption. When aircraft and other equipment at the U.S. bases were flown to safe areas or covered, losses of at least $200 to 275 million were averted. Philippine and other commercial airlines prevented at least another $50 to 100 million in damage to aircraft by taking similar actions. By heeding warnings of hazardous volcanic ash clouds from Pinatubo, commercial and military pilots avoided severe damage to their aircraft and potentially saved hundreds of lives.

During the decade after the eruption, tropical rains washed more than half of the original deposit from the volcano's slopes into surrounding lowlands, burying whole towns in mud and forcing relocation of more than 200,000 residents. USGS scientists worked with PHIVOLCS to provide both immediate and long-range warnings of volcanic debris flows called lahars. Many more lives were saved, as were countless items of personal property that could be moved out of harm's way. Engineering works eventually contained the threat.

Although savings may not always be as dramatic as those realized at Pinatubo, many lives can be saved and major property losses avoided in other volcano crises through similar relatively modest investments in volcano monitoring and eruption forecasting. The experience gained by scientists during Pinatubo's eruption and lahar crisis is being used by the USGS Volcano Hazards Program in the United States and by PHIVOLCS in the Philippines to better protect people's lives and property from the future volcanic eruptions.

More information about USGS volcano studies, including a link to the Volcano Disaster Assistance Program, is available at http://volcanoes.usgs.gov/