The Andes Mountains are made up of rocks that have been folded and faulted, as well as many hundreds of volcanoes. Because many of these volcanoes are in high and dry places there is often little information about their past activity. Sabancaya is the middle and smallest of three glacier-topped stratovolcanoes in the Peruvian Andes. Sabancaya must be younger than its neighbors because it has two large dark lava flows on its east side. But it had no known historic activity when it began erupting in December 1986. During the next 18 months of eruption it built a volcanic dome in the summit crater. Although no people were harmed, winds blew volcanic ash and gases that somehow poisoned and killed cattle.
Information Source: Shanaka L. de Silva and Peter W. Francis (1991) Volcanoes of the Central Andes. Springer-Verlag, Berlin; , p. 26-28.
Photograph Source: Space Shuttle picture STS-41G-35-020.