Four years ago Mount Pinatubo in the Philippines awoke from six centuries of slumber, sending a mass of volcanic material skyward. Finer particles made it into the upper atmosphere and were transported around the world. But most of the spew fell on local inhabitants, showering them with a mixture of ash and rain that resembled falling cement. The eight cubic kilometers of material ejected by the volcano left surrounding areas laden with ash thick and weighty enough to collapse buildings. The volcano covered the entire planet with a blanket of sorts, made up of stratospheric aerosols that scattered enough sunlight to cool the earth appreciably.
Global climate effects have since abated, but local suffering endures. Massive flows of volcanic ash, called lahars, which form in the wake of violent volcanic eruptions, persist. These viscous rivers of mud can be devastating--often more so than the explosion itself. In 1985 lahars from the eruption of Nevado del Ruiz in Colombia killed some 23,000 villagers. Around Mount Pinatubo lahars have displaced hundreds of thousands of people, who continue to wait for the mountain's loosely consolidated new surface to stabilize. But after spending nearly 600 years asleep, Pinatubo seems in no hurry to settle down.--David Schneider
SCIENTIFIC AMERICAN July 1995 Volume 273 Number 1 Page 24
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