Monitored by Servicio Geológico Colombiano's (SGC) Observatorio Vulcanológico and Sismológico de Manizales this volcano is notorious for the devastating lahars triggered by the melting of its glacial icecap during eruptive activity. In November 1985 a lahar, buried and destroyed the town of Armero. Similar but less deadly events have occurred in 1595 and 1845. The latest surface activity consisted of a series of ash explosions in 2012, which generated ashfall in the surrounding areas.