WHILE hurricane Hugo and the San Francisco earthquake focused North America's attention on natural hazards last year, the continent's inhabitants shouldn't forget volcanoes. The United States Geological Survey has warned that ``the [continuing] eruption of Redoubt volcano in Alaska and minor seismic activity at Mount St. Helens in Washington state are reminders that many Americans can be threatened by volcanic hazards.'' The survey's announcement adds that the Redoubt's widespread ash fallout - which has endangered jet aircraft - shows that ``potential hazards are not limited to people living adjacent to volcanoes.''
Volcanoes, like earthquakes, are manifestations of an active ``living'' planet. If Earth had little such activity, it probably also would not have the water and the kind of atmosphere that support its presently abundant organic life. From this perspective, we should welcome the tectonic restlessness. At the same time, the immense forces involved command respect.
This is the thrust of the Geological Survey warning. Just as people living in earthquake zones cannot neglect disaster preparedness and wise land use, so people living in volcano country cannot take safety for granted.
Volcanoes and earthquakes often arise from related causes as the great plates that make up Earth's crust move about. Generally speaking, new crust forms as magma wells up along great mid-ocean ridges, generating earthquakes and volcanoes in the process. Volcanic Iceland, which sits atop the Mid-Atlantic Ridge illustrates this.
Old seabed crust is recycled into the planet's interior along the deep sea trenches, again generating earthquakes and volcanoes. The so-called ``Ring of Fire'' that involves earthquakes and volcanoes all around the Pacific Ocean rim, including Alaska, illustrates this mechanism. Still other volcanoes may be generated by plumes of magma rising up through a crustal plate, as in the case of Hawaii.
Given this ceaseless tectonic activity - which is a vital part of our planetary environment - it's little wonder that some 50 of the 600 active volcanoes will erupt in an average year. You also have to watch out for long-dormant volcanoes. Last year, Robert Tilling of the Geological Survey reported that his historical studies show volcanoes may awaken explosively after thousands of years of sleep.
Tilling estimates that some 360 million people, globally, live on or near potentially dangerous volcanoes. Even more may be in danger of widespread ash falls. This is not a situation to cause fear. But it does call for informed alertness as human population growth and economic development bring even more people to areas of volcanic risk.
As the Geological Survey notes, there is an urgent need to produce accurate geological maps of where and in what ways volcanoes may erupt. These should then be used to put in place realistic plans for coping with eruptions when they seem imminent.