Pinatubo strato volcano seen from above

The June 12-15, 1991, eruption of 1475m Pinatubo volcano, located 100 kilometers northwest of Manila in the Philippines, was one of the largest eruptions of this century and it strongly effected some aspects of our climate.

In total the Pinatubo eruption discharged 5 billion cubic meters of ash and pyroclastic debris (including 20 to 30 megatons of sulphur dioxide and aerosols) into the atmosphere via eruption columns which were 18km wide at the base and had heights of up to 30km.

A large number of people had to be evacuated due to the erupting volcano, which had remained dormant for 6 decades.

Quick deployment of monitoring instruments and preparation of a volcanic hazards map by scientists from the Philippine Institute of Volcanology and Seismology (PHIVOLCS) and the USGS (United States Geological Service) helped scientists a lot to provide accurate warnings of impending eruptions.

These warnings were widely spread and led to the evacuation of more than 58,000 residents near the volcano, including 14,500 US military personnel from Clark Air Base (which was unusable after the eruption).  Before the climactic eruption of June 15, more than 100,000 people had left the area.

The eruption of the volcano produced a large number of micrometer-sized droplets (aerosols) of sulfuric acid which were thrown into the stratosphere.  These particles eventually spread out over the globe.  The very small droplets blocked energy coming from the Sun, the result was that the Earth cooled off a little with about a half degree centigrade.

These are satelite images of the Pinatubo volcanic cloud over a 9 day period, showing the regional dispersal of the Sulphur Dioxide plume.

These volcanic droplets had also got some other side effects, the particles catalyzed heterogeneous reactions that were probably the cause of unusually low ozone levels.

The particles were also the indirect cause of the destroying of part of the sea-nature in the Gulf of Akaba (180km long, 25km wide, 1.8km deep) because the droplets encouraged the growth of alga (which is very harmful to the sea-nature).

Another side effect was that people saw some quite abnormal sunsets which were also caused by sulfuric acid aerosols.

Information supplied by: http://volcano.und.nodak.edu