The eruption of Rabaul, Papua New Guinea, September, 1994. Photo: Australian Broadcasting Company.

In September 1994, Rabaul volcano on the Papua New Guinean island of New Britain erupted. "The death toll could have been many thousands, because about 75 percent of the houses collapsed," said Dr. Stanley Williams, a volcanologist at Arizona State University who visited the site shortly after the blast. As it turned out, only a handful of people died.

There are two reasons for this stunning success. First, in the hours leading up the eruption, observant elders who had survived a 1937 eruption of Rabaul noticed—and acted upon—several strange occurrences that had also preceded that long-ago blast. According to Ben Talai, assistant director of the Rabaul Volcano Observatory, these included the ground shaking vertically rather than horizontally (as it had done periodically since 1983); megapod birds suddenly abandoning their nests at the base of the volcano; dogs barking continuously and scratching and sniffing the earth; and sea snakes crawling ashore.

Second, residents followed a carefully designed evacuation plan.

Below are the dramatic particulars of the Rabaul evacuation, as related in "Reducing Volcanic Risk," a 1997 video produced by the International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) and the United Nations Educational Scientific and Cultural Organization (UNESCO). As Stan Williams noted, the evacuation was "a wonderful example of how people can be educated to save themselves."

Beginning in 1983, the volcano threatened to erupt again. Scientists monitoring Rabaul's crater detected a dramatic increase in earthquake activity that continued for the next 11 years. Tens of thousands of earthquakes rattled the harbor. Scientists also detected other changes caused by magma moving below. Parts of the bay were pushed up by more than a yard. Even so, no eruption took place. But the volcano's warning signs were enough for the people of Rabaul to put into place the three components of an emergency plan:

Educating the people of Rabaul about the evacuation plan.

• People were informed of the hazards they faced if the volcano actually erupted. Scientists and community leaders gave dozens of presentations to describe the effects of different types of eruptions that were likely to occur. Maps of hazardous areas were posted throughout the region. If officials should ever order an evacuation ... people would know how to get to safe areas, and they would know the location of help stations along the way.

• As a way to announce warnings clearly, the emergency plan defined four stages of alert that were determined by the intensity of the volcano's activity. For each stage of alert, the plan identified the type of warning that would be announced to the public and how it would be done. As soon as scientists determined that the volcano's activity had reached a new level, the next stage of alert was to be announced, eventually leading to an evacuation.

• Finally, everyone practiced evacuating the hazard areas to ensure that people would know where to go, what to bring, and how best to mobilize their community resources in an emergency.

Evacuation of Rabaul.

Knowing what this activity meant, people throughout the area began moving to the safe areas on their own, even though an official evacuation had not yet been declared. With help from emergency response workers, the spontaneous evacuation of 30,000 people continued through the night and into the early morning. As the last people were leaving the hazardous areas, volcanoes on both sides of the harbor began erupting.

While the city was severely damaged by ash fall in the coming weeks, only three people died during the evacuation—a tribute to the emergency plan that was prepared and practiced a decade earlier.