Today marks the 20th anniversary of one of the most significant eruptions (video - archived from news broadcasts) of the last century (or more) - the 1991 eruption of Pinatubo in the Philippines. The eruption is a landmark event for a number of reasons. First, it was one of the great successes of modern volcano monitoring - the cost in terms of lives and property were greatly reduced thanks to excellent mitigation, monitoring and emergency management. Second, it was an eruption that showed how a single event on the planet can have a global impact, as the "Pinatubo Effect" caused a 4-5 year period of cooling around the globe.
If you're looking for an excellent summary of the 1991 eruption, check out the USGS page on Pinatubo* - or, if you really want to relive the drama of the events leading up to and during the climactic eruption, watch "In the Path of a Killer Volcano," possibly the best documentary about volcanoes and volcano monitoring ever made. "In the Path of a Killer Volcano" follows the USGS scientists that headed to the Philippines on the request of PHIVOLCS (the Philippine volcano monitoring agency) to help in planning and monitoring the rising activity at Pinatubo, which at the time was a volcano that people weren't even sure when it had last erupted. The United States did have a vested interest closely monitoring Pinatubo as two major US military facilities were located within tens of kilometers from the restive volcano, so a lot of personnel and equipment was at risk. The USGS team was part of the Volcano Disaster Assistance Program (VDAP), a group only 5 years old at the time (created after the 1985 tragedy at Colombia's Nevado del Ruiz) that was set up to help countries deal with volcanoes that are showing signs of unrest and really, Pinatubo was one of the first high profile tests of the crack team of volcanologists. Throughout the documentary, you get to see the tough decisions that volcanologists have to make while watching the sometimes ambiguous signs that a volcano will give as it leads up to (or doesn't lead up to) an eruption - along with how Air Force and Philippine officials reacted to the USGS volcanologists.
