As with the majority of the Andean volcanoes, Cerro Azul is a stratovolcano, meaning that it consists of layers, or strata, of volcanic ash and lava flows. The cone of Cerro Azul has a total volume of about , and is a young feature, formed in the Holocene. It is made of agglutinated pyroclasts and some dacite-andesine lavas. The cone has a few volcanic craters; the majority of its eruptions in recorded history have originated from Quizapu Crater on the northern flank of Cerro Azul's cone. Other craters lying on the flanks of the main cone are Caracol (Snail), Crater los Quillayes, Crater la Resolana, and Crater sin Nombre (Nameless Crater). All of the craters lie between in elevation, except Quizapu, which is up the volcano. The summit of Cerro Azul is crowned by an asymmetric crater about in diameter. Pleistocene glacial activity is evident in the form of 500 meter (1,640 ft) deep struts in the volcanoes' sides. These deep cuts have revealed strata of older rock.