 On November 26 , 1846 , Cerro Azul erupted . This was the first report of activity at the volcano , and no trace of fumaroles , adjacent vents , or pre @-@ eruptive activity exists . Most descriptions of the eruption come from the backcountry herdsmen ( <unk> ) . One , who was camped in a valley approximately 7 kilometers ( 4 mi ) east of Quizapu , heard " a great noise and a cloud of ash " emanate from the mountain in the late afternoon . No precursor activity was reported , and the herdsman claimed that there were no earthquakes during the late afternoon eruption . 
