The Cerro Azul stratovolcano is at the southern end of the Descabezado Grande-Cerro Azul eruptive system. Steep-sided 3788-m-high Cerro Azul has a 500-m-wide summit crater that is open to the north. The three basaltic-andesite "La Resoloma Craters" scoria vents are located below the west flank and the two "Los Hornitos" scoria cones on the lower SW flank. Quizapu, a major vent on the northern flank of Cerro Azul, formed in 1846 during the first historical eruption at Cerro Azul, accompanied by the emission of voluminous dacitic lava flows that traveled both east into the Estero Barroso valley and west into the Río Blanquillo valley. Quizapu was later the source of one of the world's largest explosive eruptions of the 20th century in 1932, which created a 600-700 m wide, 150-m-deep crater and ejected 9.5 cu km of dacitic tephra.