Planchón-Peteroa is an elongated complex volcano along the Chile-Argentina border with several overlapping calderas. It is less than 550,000 years old and was formed by 3 different volcanoes representing different generations of the volcano: Azufre, Planchon and Peteroa.
Peteroa has been active into historical time and contains a small steaming crater lake. Historical eruptions from the Planchón-Peteroa complex have been dominantly explosive, although lava flows were erupted in 1837 and 1937.
The first volcano began its growth in the Pleistocene and constructed the basaltic-andesite to dacitic Volcán Azufre volcano.
Planchon volcano
After Azufre volcano was built, another basaltic and basaltic-andesite volcano grew 6 km to the north of it, Volcán Planchón volcano. Planchon is the northernmost basaltic volcano of the volcanic front of the Southern Volcanic Zone. It has a volume of ca. 25 km3 mainly of lava flows and very few pyroclastic rocks.
The lavas are exclusively basalt to basaltic andesite, more silica-rich rocks such as andesite or dacite are absent. Most eruptions occurred from the summit vents as there are very few dikes exposed.
Planchón volcano grew very quickly and its growth was not interrupted by glaciation, preventing deep erosion while it was growing. A large sector of Planchón and part of Azufre volcano collapsed 10,000 years ago producing Río Teno debris avalanche, removing 6 km3 of the mountain. The debris flow traveled 95 km distance. After the partial collapse of Planchon, a new edifice known as Planchon II was constructed inside the scar, but most of it was later eroded by summit glaciers and explosive eruptions from Peteroa volcano.
Peteroa Volcano
New scattered vents became active between Azufre and Planchon volcanoes and are called Peteroa volcano, the youngest volcano of the complex and the focus of recent volcanism. Peteroa has erupted a total of less than 1 km3 of lavas and not yet formed a central volcanic cone.
In contrast to Azufre and Planchón, Peteroa's magmas have differentiated more strongly and erupted mixed magmas of andesitic and dacitic composition. Many magmas from Peteroa volcano are andesites formed by magma mixing.
The amphitheater of Peteroa contains 2 phreatomagmatic explosion pits (100 m diameter and 70 m deep) and a possible third explosion pit, suggested by a 100 m diameter spiral crevasse in ice.
Magma evolution and mixing at Planchón-Peteora volcano
The volcanic system has evolved over the past 500,000 years from bimodal basaltic-dacite (primitive to highly differentiated) magmas at Azufre, to alkali-basaltic magmas at Planchón and magma-mixing formed andesite magmas at the present-day active Peteora volcano.
Sources:
- Tormey, D.R. (1989) "Gelogy and Geochemistry of the Active Azufre-Planchon-Peteroa Volcanic Center (35°15' S, Southern Andes): Implications for Cordilleran Arc Magmatism", Massachusetts Institue of Technology (PhD thesis)
- Tormey, D.R. et al (1995) "Geochemistry of the Active Azufre—Planchon—Peteroa Volcanic Complex, Chile (35°15′S): Evidence for Multiple Sources and Processes in a Cordilleran Arc Magmatic System" J. Petrology 36 (2): 265-298
