Aconcagua reaches 6,961 metres in Argentina's Mendoza Province, making it the highest mountain outside Asia and the highest point in both the Southern and Western hemispheres. Despite standing in a volcanic range and looking the part, it is not a volcano — it is uplifted and folded sedimentary and volcanic rock, pushed up by the collision that built the Andes.
Three superlatives at once
Aconcagua holds an unusual concentration of records, all of which follow from a single fact: everything higher than it is in Asia.
- Highest mountain outside Asia — no peak in the Americas, Africa, Europe, Oceania or Antarctica comes close.
- Highest in the Southern Hemisphere.
- Highest in the Western Hemisphere.
- Highest in the Americas, exceeding Denali by more than 750 metres.
The name's origin is debated. Common derivations include Quechua Ackon Cahuak, stone sentinel, and Mapudungun Aconca-Hue, referring to the Aconcagua river on the Chilean side. It sits entirely within Argentina, though the Chilean border runs only a few kilometres west.
The approach through the Horcones
The walk in from Puente del Inca runs up the Horcones valley to Plaza de Mulas, and it is a striking approach in its own right — an arid, high-desert corridor of red, ochre and grey rock with the Horcones river running grey with glacial silt and almost no vegetation at any point.
The valley also holds the penitentes, spires of hardened snow up to several metres tall that form where intense sun sublimates snow unevenly at high altitude in dry air. They are common across the high Andes and make travel across snowfields slow and awkward, and they are one of the more distinctive sights of the approach.
Not a volcano
The assumption that Aconcagua is volcanic is understandable — the Andes are full of volcanoes, several of them nearly as high, and Ojos del Salado on the Argentina–Chile border is the highest active volcano in the world at about 6,893 metres.
Aconcagua is different. It was built by compression: layers of marine sediment and older volcanic material, thrust up and stacked by the subduction of the Nazca plate beneath South America. Its summit rock includes material laid down in a shallow sea.
The region has a further geological peculiarity. Beneath this section of the Andes the subducting plate flattens out rather than descending steeply — a flat-slab segment — which suppresses the melting that generates volcanoes and instead concentrates compression and uplift. Hence a zone with the continent's highest peak and comparatively few active volcanoes.
The Normal Route, and why altitude is the whole problem
Aconcagua's north-west or Normal Route is non-technical. It is a long, high walk on scree and snow with no roped climbing required in ordinary conditions, and it is often described as the highest mountain in the world that can be ascended without technical skills.
That description has killed people. At 6,961 metres, atmospheric pressure is roughly 40 per cent of sea level, and climbers arriving from Mendoza — at 750 metres — face a very large altitude gain over a short period. High-altitude pulmonary and cerebral oedema are the principal causes of death, and the mountain records several fatalities in most seasons.
The other factor is wind. Aconcagua stands in the path of the Southern Hemisphere westerlies with nothing upwind of it, and the viento blanco — white wind — is a storm condition combining extreme wind with driven snow, in which movement becomes impossible and temperatures with windchill fall far below anything the thermometer shows. Summit day frequently turns on whether that wind is blowing.
The Polish Glacier route on the east side is the significant alternative and does involve technical ground, though the glacier itself has thinned substantially and many parties now use a traverse variant instead.
What the summit is made of
Aconcagua's summit rock includes marine limestone and volcanic material from the Mesozoic, deposited when this part of the Andes lay under a shallow sea on the western margin of South America. That rock has been thrust upward and stacked by compression over the last twenty million years or so.
The mountain therefore records the same sequence as the Himalaya in miniature: sediment laid down under water, then lifted several kilometres into the air by plate convergence. Marine fossils near the top of a 6,961-metre peak are, in that sense, exactly what should be expected.
1897, and the guide who reached the top first
The first recorded ascent was on 14 January 1897 by Matthias Zurbriggen, a Swiss guide working for an expedition led by the British climber Edward FitzGerald.
Zurbriggen went to the summit alone; FitzGerald, defeated by altitude sickness on several attempts, never reached it. It is one of the clearer early cases of a professional guide making a first ascent that the expedition's named leader could not, and Zurbriggen's role was recognised at the time more generously than was common in that era.
There is evidence that the Inca were on the mountain long before. A mummified boy of around seven years old, an Inca capacocha sacrifice, was found at about 5,300 metres on the south-west ridge in 1985, along with textiles and figurines, indicating high-altitude ritual activity on Aconcagua roughly 500 years ago. Inca remains have been found on numerous Andean summits, some above 6,000 metres.
The south face
The mountain's serious mountaineering is on the south face — a wall of roughly 3,000 metres of rock, ice and hanging glacier, first climbed by a French expedition led by René Ferlet in 1954 in an ascent that took days of committing climbing.
It is one of the great faces of the Andes and a completely different proposition from the walk-up on the other side. Reinhold Messner, among others, has described it as one of the most dangerous large faces he encountered, principally because of rockfall and the instability of its ice.
The contrast between the two sides of one mountain is extreme even by Andean standards: a route that guided clients complete in a couple of weeks with no technical skills, and a wall that has killed accomplished alpinists.
The park, the rubbish, and the crowds
Aconcagua sits in a provincial park, and access is regulated by permit with fees varying by season and nationality. Numbers run to several thousand climbers and trekkers a year, concentrated in the December-to-February window.
That traffic created a waste problem severe enough to require intervention. Park authorities now operate a system in which climbers are issued numbered bags and must return their waste, including human waste from the high camps, and permits can be withheld from operators who fail to comply. Plaza de Mulas, the main base camp at around 4,300 metres, functions as a small seasonal town with medical staff, and helicopter evacuation is available — one reason the fatality rate is lower than the altitude alone would predict.
Mules do the load-carrying on the approach, which is why the camps are named for them, and the walk-in through the Horcones valley is a striking approach through arid, colourful, almost vegetation-free terrain.
The season, and the wind
The climbing season runs from roughly mid-November to mid-March, with the best conditions usually in January. Outside that window the mountain is effectively closed: the park does not issue climbing permits, and conditions on the upper slopes are beyond what a normal expedition is equipped for.
Within the season, the limiting factor is the viento blanco. Aconcagua stands almost alone in the path of the westerlies, and summit-day winds of over 100 km/h are common enough that expeditions build several spare days into their schedule specifically to wait one out. Parties frequently reach high camp and sit there for days before either getting a window or descending having never left the tent.
Guided itineraries typically run 18 to 21 days for that reason. A shorter schedule that assumes the first summit attempt will succeed has a poor record.
Records, and the extremes of the mountain
Aconcagua's non-technical route and high altitude have made it a target for speed records, with the fastest ascents from the park entrance measured in hours rather than days — Karl Egloff and Kilian Jornet have both set marks there.
It has also seen a wide age range of summiteers, including climbers in their nineties and children under ten, which has prompted periodic debate about whether the park should impose limits. The park's medical checks at base camp — pulse oximetry and examination by staff doctors, with authority to refuse permission to continue — are among the more interventionist arrangements on any major mountain.
Aconcagua among the Seven Summits
For most people pursuing the Seven Summits, Aconcagua is the step between the walking peaks and the serious ones:
- Higher than Kilimanjaro and Elbrus by a substantial margin, so it is the first genuine test of high-altitude tolerance.
- Less technical than Denali or Vinson, and vastly less than Puncak Jaya.
- Cheaper and more accessible than most, with a road reaching close to the trailhead from Mendoza.
- Riskier than its grade suggests, for the same reason as Elbrus — non-technical ground at an altitude that is genuinely dangerous.
The Andes as a whole are the longest continental mountain range in the world, running some 7,000 km along South America's western edge, and Aconcagua is their high point. Our Andes guide covers the range's full extent.