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. Quizapu Crater 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. The Quizapu Crater is almost perfectly circular, and rises to a prominence of above the surrounding portions of the volcano. Cresting at in elevation, Quizapu is one of the highest known Plinian craters. The radius of the crater floor, which is the current inner vent, is around , while the radius of its rim is . The crater floor lies at , and the rim lies above that, giving the walls an average slope of 34–35 degrees (close to the angle of repose). The western wall is cut by two long, dacitic lava flows: probably the remnants of a dome or an eruption. The crater is surrounded by debris from its 1932 eruption, and topped by layers— thick—of mafic scoria and ash. Climate and vegetation Cerro Azul is situated in a Mediterranean climate zone, characterized by hot and dry summers but mild and wet winters. The temperatures and precipitation are strongly dependent on topography. In the Andes the annual average maximum temperatures lie in the range , while minimum temperatures are below . Annual precipitation is up to 800 mm (31.5 inches). Vegetation in the Andes varies with elevation. Above 1,600 meters (5,249 ft) the slopes of mountains are covered by Alpine-like steppe, while below there are zones of Nothofagus forest, Hygrophilous forest,