 This first recorded eruption of Cerro Azul was effusive , and formed the volcanic vent at Quizapu . <unk> – dacite lava erupted with small masses of tephra , which had been <unk> shortly before the eruption . Lava flowed over the Estero Barroso Valley and westward into the Río <unk> Valley . By November 28 , the volcano appeared at rest , and the herdsman returned to the place of first observation . There , they found a blocky lava field . The lava was still hot , fuming and crackling with gas and flame . Fascinated by the volcano , Ignacy <unk> traveled to Chile to study the field and found its width to be 8 – 9 square kilometers ( 3 @.@ 1 – 3 @.@ 5 sq mi ) . By 1992 the field had grown to twice that size . 
