Controlled explosion: Pintubo, Philippines

In the shadow of the volcano

The eruption of Pinatubo in 1991 offers sharp contrasts with the tragedy of Nevado del Ruiz (opposite). While Pinatubo produced one of the largest volcanic outbursts of the century, it did not produce the greatest volcanic catastrophe of the century. More than a million people lived within striking distance of Pinatubo, including those in the US Clark air base, 25 kilometres from the crater. But unlike many regions prone to eruptions, the Philippines had the administrative infrastructure to deal with the crisis. This eruption was the first to be monitored from start to finish - by the Philippine Institute of Volcanology and Seismology, along with US colleagues.

Soon after the eruption began on April 2, a ten-kilometre danger zone was designated around the volcano. Five thousand members of the Aeta tribe, who lived on the mountain, were evacuated to refugee camps, a rapid survey of the hitherto little-known geology of Pinatubo was made, and five alert levels were established in relation to the expected activity. The alert level that the eruption had reached was published daily.

The first hazard map was issued on May 23 and sent to the media and to the relevant administrative hierarchy, from President Aquino through to village leaders. The threatened people were told what to expect with the aid of a graphic film on volcanic hazards made by the famous French volcano watchers, Maurice and Katia Krafft, themselves killed by a Japanese volcano in 1991. As the molten rock approached the surface, alert levels increased, danger zones were extended and more people were evacuated to refugee camps. About 74,000 people were removed from the danger zones, including the US personnel from the air base.

Pinatubo erupted 1,500 times as much volcanic material as Nevado del Ruiz, but the organised response to the crisis meant that direct casualties of the eruption were fewer than 300, although about 900 people - mainly Aetas - fell victim to disease in the refugee camps.

Since the eruption, every monsoon has generated mudflows from the thick ash covering the volcano, necessitating continued surveillance. Although the eruption was well documented, regrettably, the US Geological Survey did not feel able to spare the expense of publishing these findings. Fortunately, wiser counsels prevailed at the University of Washington and at the Philippine Institute of Volcanology and Seismology. They jointly published what has become the most useful and up-to-date manual of how to deal with a volcanic emergency.