 Quizapu , which formed during the 1846 eruption , is the most prominent crater . It is also known as Cerro del Medio ( " Middle Hill " ) or Volcan Nuevo ( " New Volcano " ) . The volcanic vent formed during an effusive eruption involving hornblende – dacite flows accompanied by tephra , and the crater was excavated by phreatic and Strombolian eruptions between 1907 and 1932 . <unk> @-@ up pressure within the volcano spawned an enormous Plinian eruption in 1932 . The volume of lava ejected during this single event is roughly equal to that ejected during the rest of the eruptive history at Quizapu , since its formation in 1846 . Although 9 @.@ 5 cubic kilometers ( 2 @.@ 3 cu mi ) of material was ejected , no subsidence was detected from the removal of magma . Because of aerodynamic drag , a Plinian eruption excavates a circular crater . As the earlier eruptions had already formed an approximately circular caldera , the Plinian eruption was able to proceed efficiently , with minimal drag and minimal reshaping of the crater . 
