• Mount Pinatubo erupted in 15 June 1991
  • The second-largest volcanic eruption of the 20th century.
  • A magnitude 7.8 scale richter hit Luzon Island.
  • Mount Pinatubo in the Philippines is one of a chain of volcanoes forming the Luzon volcanic island arc.
  • The second-largest eruption to affect a densely populated area. 
  • The arc parallels the West coast of Luzon and reflects the subduction zone along the Manila trench to the West. The steep, easterly dipping subduction of the Eurasian Plate started about 10 million years ago and produce a line of active volcanoes through the northern Philippines. 
  • The earthquake was struck about 60 miles (100 km) northeast of Mount Pinatubo on the Luzon Island. 
  • From 7-12 June, the first magma reached the surface of Mount Pinatubo. It went out to form a lava (no explosive). 
  • Magma rising toward the surface from more than 20 miles (32 km) beneath Pinatubo triggered small and caused powerful steam explosions that blasted 3 craters on the North flank of the volcano. 
  • June 12 (Philippine Independence Day), millions of cubic yards of gas-charged magma reached the surface and exploded. 
  • June 15, the eruption creating a cloud of volcanic ash that rose as high as 22 miles (35 km) into the air and grew to more than 300 miles across, turning day into night over central Luzon. The ash was formed into typhoon at lower altitudes and also blew the ash to the southwestward. The volcanic ash (sand-and silt-size grains volcanic minerals and glass) and larger Prumice Lapilli (Frothy Pebbles) blanketed the countryside. The ash fell as far away as the Indian Ocean. 
  • 16 June 1991, The pyroclastic flows go down the flanks of Mount Pinatubo, filling once-deep valley as much as 200 m thicks. The eruption removed the magma and rock from below the volcano to form a large volcanic depression (Caldera) 2.5 Km across. The new summit height of Mount Pinatubo is approximately 1485 m above sea level. 
  • From July - October 1992, a lava dome was built in the new Caldera as fresh magma rose from deep beneath Pinatubo. 
THE IMPACT:
  • 3 million people forced the eruption 
  • about 200,000 people were evacuated 
  • all resources (rice paddies and  sugar canes) were buried by lahars 
  • Aircraft, railway and other transportations were covered by the ash and it costs about $100 million in damage 
  • over 20 million tonnes of sulphur dioxide were injected into the stratosphere in Pinatubo's eruptions 
  • It causes global temperatures 
  • The temperature on the earth drop about 0.5 degree celsius, between 1991 and 1993. Due to the sulphuric acid, which blocked some of the sunlight from reaching the Earth 
IN THE FUTURE? 
  • The scientists estimated that it will be erupt soon in the future 
  • since the eruption, ash deposits have also been remobilised by monsoon and typhoon rains to from deadly lahars 





GOOD NEWS? 
  • The monitoring of Mount Pinatubo in 1991 prevented property looses of at least $250 million
  • 5000 lives were saved.
  • Total costs due to eruption were only about $51 million







Sources: 
  1. USGS 
  2. geography: Teacher Resources Book 2003