Puyehue (; Spanish pronunciation: [puˈʝewe]) and Cordón Caulle are two coalesced volcanic edifices that form a major mountain massif in Puyehue National Park in the Andes of Ranco Province, in the South of Chile. In volcanology this group is known as the Puyehue-Cordón Caulle Volcanic Complex (PCCVC). Four volcanoes constitute the volcanic group or complex, the Cordillera Nevada caldera, the Pliocene Mencheca volcano, Cordón Caulle fissure vents and the Puyehue stratovolcano. Like most stratovolcanoes in the Southern Volcanic Zone of the Andean Volcanic Belt, Puyehue and Cordón Caulle are along the intersection of a traverse fracture with the larger north–south Liquiñe-Ofqui Fault. The volcanic complex has shaped the local landscape and produced a huge variety of volcanic landforms and products over the last 300,000 years. Cinder cones, lava domes, calderas and craters can be found in the area apart from the widest variety of volcanic rocks in all the Southern Zone, for example both primitive basalts and rhyolites. Cordón Caulle erupted shortly after the Great Chilean Earthquake. With a magnitude of 9.5, it remains the largest recorded earthquake in history. Apart from this, the Puyehue-Cordón Caulle area is one of the main sites of exploration for geothermal power in Chile. Geothermal activity is manifested on the surface of Puyehue and Cordón Caulle as several boiling springs and fumaroles. Most of the stone artifacts found in Pilauco Bajo (dated to c. 12.5 to 13.5 ka BP) are made of dacite, rhyodacite and rhyolite from the Puyehue-Cordón Caulle. Yet these rocks were imported by humans to the site as nearby rivers have not transported them.
Approach and ascent From the south, the Cordón Caulle can be approached from Fundo El Caulle on Route 215-CH, which goes from Osorno to Bariloche in Argentina through Samoré Pass. Some 1,000 m up on forested slope there is a campsite and mountain shelter. According to the homepage of Puyehue National Park the shelter can be reached after four hours walking. The access through El Caulle is not public as it is not inside Puyehue National Park; and an entrance fee of 10,000 CLP, as of 2009, has to be paid, of which 3,000 are refunded if visitor packs out his garbage. From the north, there are tracks from the vicinities of Nilahue Valley near Ranco Lake. The track ascends ca 1,000 m through dense forest to the Cordón Caulle area. From the relatively flat Cordón Caulle there is further ca 600 m of ascent over tephra and loose rocks to the summit of Puyehue. In the Nilahue area there are arrieros who offer horseback trips to Cordón Caulle.
Geography Puyehue, Cordón del Caulle, and Cordillera Nevada form a northwest trending massif in the Ranco Province of the Andes. The three volcanoes are coalesced. Puyehue is located in the southeast, Cordón Caulle in the center, and Cordillera Nevada, which owes its name to its often snowy appearance from the relatively densely populated Chilean Central Valley, is at the northwestern end. The massif is located between two lakes, Ranco Lake in the north and Puyehue Lake in the south. The fact that Puyehue volcano is named after Puyehue Lake reflects that it is better seen and more accessible from the south. Cordillera Nevada is a 9 km (6 mi) wide semicircular caldera and corresponds to the remnants of a collapsed volcano. Cordillera Nevada covers an area of 700 km2 (270 sq mi). Cordón Caulle is a northwest trending ridge that hosts a volcanic-tectonic graben in which a fissure vent is developed. Puyehue Volcano is a stratovolcano located on the southeastern end of Cordón Caulle, just east of the main fault of the Liquiñe-Ofqui Fault Zone. Its cone hosts a 2.4 km (1.5 mi) wide crater, and products of Puyehue volcanism cover an approximate area of 160 km2 (62 sq mi).
Flora The lower parts of the mountains are covered by an alpine plant association of Valdivian temperate rainforest, where plant species such as Chusquea coleou and Nothofagus dombeyi are common. The tree line, lying around 1,500 m (4,921 ft) elevation, is mostly made up of Nothofagus pumilio. Above this line lies a volcanic desert and alpine tundras. The main plant species present in these high elevations are Gaultheria mucronata, Empetrum rubrum, Hordeum comosum and Cissus striata.
Geologic history The volcanic complex that comprises Puyehue, Cordón Caulle and Cordillera Nevada has a long record of active history spanning from 300,000 years ago to the present. The older parts of the Cordillera Nevada caldera and Mencheca volcano reflect even older activity from the Pliocene or the early Pleistocene. In the past 300,000 years, there have been a series of changes in magmatic composition, locus of volcanic activity, magma output rates and eruptive styles.
Ancestral volcanoes
Some 300,000 years ago, important changes occurred in the area of Puyehue. The old Pliocene volcano Mencheca, currently exposed just northeast of Puyehue's cone, declined in activity. This decline was probably due a regional change in the location of the active front of the Southern Volcanic Zone that also affected other volcanoes such as Tronador and Lanín. The relocation of the active front gave rise to new volcanoes further westward or increased their activity. The formerly broad magmatic belt narrowed, retaining vigorous activity only in its westernmost parts. Associated with these changes are the oldest rocks of PCCVC, those that belong to Sierra Nevada. Sierra Nevada grew over time to form a large shield volcano, during the same time Cordón Caulle was also being built up having rather silicic products compared to coeval Sierra Nevada and Mencheca. The oldest rocks from proper Puyehue volcano are 200,000 years old, representing the youngest possible age for this volcano. It is estimated that some 100,000 years ago in the period between Río Llico and Llanquihue glaciation a large ignimbrite called San Pablo was produced. This ignimbrite covers an estimated area of 1,500 km2 (370,658 acres) immediately west of Cordillera Nevada, stretching across the Chilean Central Valley almost reaching the Chilean Coast Range. The San Pablo ignimbrite has been associated with the formation of the Cordillera Nevada Caldera.
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