Early warning for the 1991 eruptions of Pinatubo volcano: A success story

Raymundo S. Punongbayan1, Christopher G. Newhall2
1Philippine Institute of Volcanology and Seismology, Department of Science and Technology, C.P. Garcia Ave, Diliman, Quezon City, Philippines.
Tel.: +63-2-9 26-26 11, Fax: +63-2-9 29-83 66,
E-mail: rsp@philonline.com.ph
2United States Geological Survey/University of Washington Volcano Systems Center

The success or failure of a warning system can be gauged in terms of the number of lives (and value of assets) lost to or saved from a disaster causing event. In these terms, the early warning system used at Pinatubo Volcano in 1991 can be considered a success story – the death toll of 250-300 out of the 20,000 immediately at risk was small despite the magnitude and violence of the eruption which was one of the world’s biggest eruptions this century. This success can be attributed to a number of factors: early detection of the unrest, timely identification of hazards and delineation of vulnerable areas to them, successful application of state-of-the-art monitoring and surveillance techniques, accurate prediction of the most destructive phase of the eruption, timely issuance and dissemination of easily understood warnings, prompt action of key civil defence officials and disaster response workers, and timely evacuation of the majority of inhabitants at risk. What made the Pinatubo story a classic are not only its success factors but also its near-misses – the things that could easily have gone wrong but luckily did not, which provide valuable lessons for developing warning systems in particular and volcanic risk mitigation plans in general. The positive aspects of the experience highlighted the value of the following: state-of-the-art monitoring equipment and techniques, international co-operation based on mutual respect, sustained intensive public education on volcanic hazards; active involvement of selected scientists as the designated spokespersons in awareness promotion and warning dissemination; open and speedy communication lines between the science people on the one hand and the civil defence officials on the other; and good relations between scientists and the media. The near-misses or potentially negative aspects of the experience underscored the need to conduct geologic data base studies and hazard zonation on all active volcanoes long before the onset of unrest. We were lucky because Pinatubo gave us sufficient lead time to conduct reconnaissance geological studies and mapping of deposits of its past eruptions thus enabling us to forecast the life-threatening hazards when it decides to erupt and to warn/educate concerned sectors into taking appropriate protective actions. We know that we will not always be as lucky. Hence, efforts will now be focussed on detailed studies and mapping of the unmonitored active volcanoes and on conducting in communities-at-risk an à-la-Pinatubo education campaign that would erode their indifference, scepticism and hostility to long-term action plans for volcanic disaster mitigation.