Plinian eruption
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. Pent-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 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.