Planchón-Peteroa, Complex volcano at Argentina-Chile border

Planchón-Peteroa is a complex volcano on the Argentina-Chile border formed by Volcán Planchón, Volcán Peteroa and Volcán Azufre, with several overlapping calderas. Its highest point, Volcán Peteroa, reaches 3,977 metres above sea level. Peteroa has a crater lake, and the Lagunas de Teno lie at the foot of Planchón.

The Planchón-Azufre-Peteroa group formed during the Pleistocene. About 11,500 years ago the western half of Planchón's edifice collapsed, sending a debris avalanche down the Teno River for 75 km toward Chile's Central Valley; the event, known as the Lahar Teno, is apparently linked to a Plinian eruption that spread pumice tephra only on the Argentine side. Recorded activity at Peteroa begins in 1660, with a large eruption in 1751 and another on 3 December 1762 recorded by Abbot Juan Ignacio Molina, which destroyed a central cone inside the caldera and opened the Chilean side.

The name Peteroa comes from Mapuche words püthen (to burn) and rogh or roa (branches), meaning burnt branches. The volcano lies in Romeral commune, Curicó province, Maule region, on the Chilean side, and in Malargüe department, Mendoza province, on the Argentine side. The Vergara International Pass crosses the area, and Lagunas de Teno sits at the foot of Planchón.

The Vergara International Pass lies in this area, linking Argentina and Chile; Lagunas de Teno sits at the foot of Volcán Planchón. Chilean access runs through Romeral in the Curicó province, Maule Region, and Argentine access through Malargüe Department, Mendoza. Ash from the September 2010 eruptions drifted southeast into Argentina, and Chilean authorities declared a yellow alert for Romeral, Curicó, Teno and Molina in December 2018.

The complex comprises three distinct volcanic formations: Volcán Planchón, Volcán Peteroa, and Volcán Azufre, each displaying separate geological characteristics. This arrangement allows scientists to observe different volcanic processes occurring in proximity to one another.