Monte Pissis is an extinct volcano on the border of the La Rioja and Catamarca provinces in Argentina, 25 km to the east of the Chilean border and about 550 km north of Aconcagua. The mountain is the third-highest in the Western Hemisphere. Monte Pissis is named after Pedro José Amadeo Pissis, a French geologist who worked for the Chilean government. Due to its location in the Atacama Desert, the mountain has very dry conditions but features an extensive glacier, with crevasses, which is unique in the region. The peak is the highest summit on Earth without a permanent glacier.

Elevation

A 1994 Argentine expedition claimed —using GPS technology available at the time— that the elevation of Monte Pissis was 6882 m, higher than Ojos del Salado. Ten years later, with the use of higher precision systems, several other surveys proved that those measurements were inaccurate: in 2005, an Austrian team performed a DGPS survey of Pissis' summit and found the elevation to be 6793 m. In 2006 an international expedition surveyed the height on the summit, and found results in agreement with an elevation around 6800 m. This was later confirmed by a 2007 Chilean-Argentine-European expedition, which surveyed both Ojos del Salado and Monte Pissis and provisionally found the former to be 6891 m and the latter 6793 m.

Geology

Monte Pissis is a large andesitic-dacitic volcanic centre. It was formed between 6.6 and 6.2 million years ago. Like Cerro Bonete Chico it is one of the large volcanic complexes formed at that time over a deforming Nazca slab. Volcanism in the area ceased about 2 million years ago. Monte Pissis, Cerro Bonete Chico and Incapillo form a large volcanic complex that is among the highest in the world. Incapillo formed after Monte Pissis had ceased erupting, and hydrothermal activity at Incapillo may continue to this day.

Climbing

Until recently, this mountain had received very little attention. The first successful recorded ascent was made in 1937 by Polish climbers Stefan Osiecki and Jan Alfred Szczepański of the Second Polish Andean Expedition. The mountain was not climbed again until 1985. The advent of mining in the area has resulted in the construction of basic roads in the last 15 years. This has helped tourism to develop in the Atacama Desert, and now more people ascend the mountain, usually with a previous stop in Fiambalá to organise the climb. Approaching it from neighbouring Chile is also possible but involves a longer route. As the mountain is very high and remote, a long approach is required but the ascent is easy and does not require any specific climbing skill. Nevertheless, warm clothing and good shoes are essential, as the temperature during the night can drop as low as -30 C and winds can be very strong. Usually most teams ascend the peak during December to March, the warmest period of the year. The peak is one of the most heavily glaciated peaks in the Atacama Desert, although the glaciated area starts only at 5900 m, and the size of the glacier is small compared to the overall surface of the mountain. From the base of the mountain at 4500 m, several days of hiking are required. The summit is usually reached directly from a high camp at 5900 m at the edge of the glacier.