Cerro Azul (, blue hill in Spanish), sometimes referred to as Quizapu, is an active stratovolcano in the Maule Region of central Chile, immediately south of Descabezado Grande. Part of the South Volcanic Zone of the Andes, its summit is above sea level, and is capped by a summit crater that is wide and opens to the north. Beneath the summit, the volcano features numerous scoria cones and flank vents. Cerro Azul is responsible for several of South America's largest recorded eruptions, in 1846 and 1932. In 1846, an effusive eruption formed the vent at the site of present-day Quizapu crater on the northern flank of Cerro Azul and sent lava flowing down the sides of the volcano, creating a lava field 8–9 square kilometres (3–3.5 square miles) in area. Phreatic and Strombolian volcanism between 1907 and 1932 excavated this crater. In 1932, one of the largest explosive eruptions of the 20th century occurred at Quizapu Crater and sent of ash into the atmosphere. The volcano's most recent eruption was in 1967. The South Volcanic Zone has a long history of eruptions and poses a threat to the surrounding region. Any volcanic hazard—ranging from minor ashfalls to pyroclastic flows—could pose a significant risk to humans and wildlife. Despite its inactivity, Cerro Azul could again produce a major eruption; if this were to happen, relief efforts would probably be quickly organized. Teams such as the Volcano Disaster Assistance Program (VDAP) are prepared to effectively evacuate, assist, and rescue people threatened by volcanic eruptions. Geography and geology Regional setting Volcanism in the Chilean Andes is caused by subduction of the Nazca and Antarctic tectonic plates under the South American Plate. Volcanoes in Chile occur in the Central (CVZ), South (SVZ), and Austral Volcanic Zones (AVZ). The gap that separates the Central and South Volcanic Zones is caused by shallow-angle subduction in the Pampean flat-slab segment where the more buoyant Juan Fernández Ridge subducts under the South American continent. This buoyant region prevents the slab (subducting tectonic plate) from diving deep into the mantle, where the heat and pressure would destabilize the mineral chlorite, releasing water that would in turn cause melting and volcanism. The Patagonian Volcanic Gap, which separates the South and Austral Volcanic Zones, is caused by the subduction of the Chile Ridge, though it is less clear whether this gap also is due to flat-slab subduction; it may instead arise