| Recognition of the volcanic unrest at Mount Pinatubo in the Philippines began when steam explosions occurred on April 2, 1991. The unrest culminated ten weeks later in the world's largest eruption in more than half a century. Volcanologists of the Philippine Institute of Volcanology and Seismology (PHIVOLCS), joined in late April by colleagues from the U.S. Geological Survey (USGS), successfully forecast the eruptive events and their effects, enabling Philippine civil leaders to organize massive evacuations that saved thousands of lives. The forecasts also led to the evacuation of Clark Air Base (U.S. Air Force), located just east of the volcano. Nevertheless, coincidence of the climactic eruption on June 15, 1991, with a typhoon led to more than 300 deaths and extensive property damage, both caused primarily by the extraordinarily broad distribution of heavy, water-saturated tephra-fall deposits. Runoff from monsoon and typhoon rains is eroding and redistributing the voluminous pyroclastic deposits emplaced during the eruption. The resulting lahars, floods, and sedimentation have exacerbated the already severe social disruption and will be an enormous recurring problem in future years. -- Wolfe, 1992 |
