Edward W. Wolfe 1992 <p>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.&nbsp;</p> application/pdf en U.S. Geological Survey The 1991 eruptions of Mount Pinatubo, Philippines article