Why did it occur?

It is first important to understand that volcanic activity can be triggered by movement of the tectonic plates in the earth’s crust.  Rantucci (1995) provides more specific detail about the plates in the Luzon area, “Major tectonic lineaments are the double-sided seduction due to the convergence of the Eurasian and Philippine Sea Plates and the horizontal slip motion along the Philippine Fault” (p. 33).  This creates the opportunity for any of these plates to shift which could cause events leading to disasters such as the Mount Pinatubo eruption.


There were a number of documented incidences that were attributed to the awakening of Mount Pinatubo.  One of the early indications was document by researchers Bernard et. Al. (1999) “increased solfataric activity in August 1990 was detected, which was likely released due to the earthquake along the Philippine-Giddig fault”.  They go on to explain the first signs of volcanic activity in April 1991 were in the form of small amounts of ash ejecting from six vents on the northern slope of the main cone” (Petrology and Geochemisty of the 1991 Eruption Products of Mount Pinatubo, para. 4).

There were indirect and direct factors that contributed to the actual eruption of the Volcano.  Rantucci (1995) explains, “the Luzon earthquake that occurred in July 1990 was indirectly responsible awaking the dormant volcano but the actual triggering factor n June 12, 1991 was the subsurface block rearrangement which started after the 1990 quake which went on for months” He goes on the explain “ the aftershock period modified the pre-existing  equilibrium and affected the rock basement of the Central Valley, thus favoring magmatic injections into the Pinatubo chamber, which ignited the volcano.


A large portion of the volcano was destroyed and a large amount of gases were released into the air which had a significant impact on the surrounding area and effects of the gases released were recorded in areas many miles away from the actual disaster site