extending into the air, were sighted. Phenocrysts were similar to the effusive eruption in 1846. Soon after, both the Tinguiririca and Descabezado Grande volcanoes began erupting, sending clouds of ash into Argentina. The eruption had a Volcanic Explosivity Index (VEI) of at least 5. Since the eruption of 1932 Quizapu has been quiet. In 1949 and 1967 small ash clouds were reported, while in the 1980s there were no signs of activity other than fumaroles. Threats and preparedness Cerro Azul is in the South Volcanic Zone, where many volcanoes pose a threat to human life. Among the other active volcanoes of the South Volcanic Zone are Mount Hudson, Llaima, and Villarrica. Villarrica and Llaima together have more than 80 reported episodes of volcanism since 1558, and at least 40 South Volcanic Zone volcanoes have had Holocene-age eruptions. Every known type of eruption (Hawaiian, Strombolian, Plinian, subplinian, phreatic, phreatomagmatic, and Vulcanian) has occurred at some point in the range. Cerro Azul itself has experienced phreatic, Strombolian, and Plinian activity in human history. The type of eruption tends to correspond with lava composition. Strombolian eruptions at Llaima, Antuco, Villarrica, and elsewhere have been produced by basaltic to basaltic–andesitic activity. Dacitic to rhyolitic lavas have been linked to subplinian and Plinian eruptions, such as those at Quizapu (1932) and Hudson (1991). Because of this variability, volcanic hazards from Cerro Azul and the surrounding region could come in many different forms. Historical eruptions typically have produced lahars, lava flows, and ashfalls. Lava flows and lahars could wipe out entire cities or towns. Ashfall produced by explosive eruptions could interfere with air traffic. Most threatening of all is the risk of pyroclastic flows or avalanches, which have historically traversed as far as in the region. Past eruptions of Quizapu Crater ejected enormous amounts of ash that traveled as far as Brazil. After the 1932 eruption, the local vegetation was devastated, and the area remained barren until the 1990s, though human life was not impacted. Despite the extent of its eruptions, the threat to humans from Quizapu is relatively small because of the remote location of Cerro Azul. Nevertheless, the size of past eruptions is large enough for scientists to be worried. Evidence of a potentially deadly threat lies in a lahar at Descabezado Grande. Historically, lahars have killed thousands in the Andes. There is, however, a possibility that a large reservoir of rhyodacite magma may