Highest Mountain in South America: How Aconcagua’s Height Is Measured, and the Andes Top 10

The highest mountain in South America is Aconcagua, in Argentina's Mendoza Province about 15 km from the Chilean border, with a summit usually given as 6,961 m (22,838 ft) above sea level. A 2012 survey by the National University of Cuyo measured it at 6,960.8 m, and Wikipedia's article now quotes 6,967 m, but every figure leaves it the highest mountain outside Asia and the highest in both the Western and Southern Hemispheres. It is no longer a volcano: an active stratovolcano until the Miocene, it was lifted off its volcanic root by thrust faults about 8 to 10 million years ago, as the Nazca Plate pushed beneath South America at a shallower angle. The first recorded ascent was made on 14 January 1897 by the Swiss guide Matthias Zurbriggen, a member of Edward FitzGerald's British expedition. Second is Ojos del Salado (6,893 m) on the Argentina–Chile border, the highest volcano on Earth.

Three numbers for one summit set the theme for this ranking. Below 7,000 m, in the dry Andes where many peaks are rarely climbed, how a height was measured matters as much as the mountain itself, and several widely reported "records" turned out to be survey errors.

Three numbers for Aconcagua: 6,962, 6,960.8 and 6,967

A mountain's height is its elevation above mean sea level, or more precisely above the geoid, the shape sea level would take if it continued under the continents. Surveyors once reached that figure by triangulation from distant stations and by barometers; today a GPS receiver on the summit measures height above a mathematical ellipsoid, and a geoid model converts it to height above sea level. Different geoid models, a few metres of snow, and the choice between the rock summit and the snow surface all move the result.

Aconcagua shows this in miniature. Wikipedia's own "List of highest mountains on Earth" gives 6,962 m and ranks it 189th in the world, behind 188 summits that are all in Asia. The 2012 National University of Cuyo report put it at 6,960.8 m. The figure in its article's opening line is 6,967 m. The spread is about six metres, which does not affect any ranking: the next mountain down is nearly 70 m lower. The mountain itself lies 112 km northwest of the city of Mendoza inside Aconcagua Provincial Park, and its largest glacier, the Horcones Inferior, is roughly 10 km long.

Aconcagua is also a prominence giant. It is the highest point of a whole continent, so its prominence, the height it rises above the lowest saddle connecting it to anything taller, equals its full elevation, and that makes it the second most prominent peak on Earth after Everest. The normal route from the north needs no ropes, but at the summit air pressure is roughly 40% of sea level, and the mountain averages about three deaths a year.

Ojos del Salado and the 1956 claim of 7,084 metres

For a few years in the 1950s, newspapers reported that Ojos del Salado might be higher than Aconcagua. In 1955 an expedition from Tucumán climbed a peak south of the volcano, mistook it for Ojos del Salado, and suggested it could top Aconcagua. In 1956 a Chilean party measured 7,084 m with a barometer, a method unreliable at that precision, and the press again reported it as fact. By 1957 Argentina's official figure was 6,870 m and Chile's 6,880 m.

The question was settled by better instruments. An American Alpine Club expedition in 1956 used geodetic methods to fix 6,885.5 m (±3 m), clearly below Aconcagua. In 1989 Francesco Santon of the University of Padua, with Argentine help, used GPS and found 6,900 m (±5 m). A 2007 Chilean–Argentine–European expedition provisionally measured 6,891 m, and 6,893 m is the figure most lists use now.

Whatever the decimal, Ojos del Salado holds other records. It is the highest peak in Chile and the highest volcano in the world, its last eruption dated to around 750 CE, and a permanent crater lake about 100 m across at 6,480 to 6,500 m is the highest lake of any kind on Earth. Its first ascent was made on 26 February 1937 by the Polish climbers Jan Alfred Szczepański and Justyn Wojsznis. It can be climbed from either country, and an international highway between Argentina and Chile crosses just north of the massif.

Monte Pissis and the 1994 GPS reading of 6,882 metres

The next challenger came in 1994, when an Argentine expedition used the GPS equipment of the time to measure Monte Pissis, an extinct volcano on the La Rioja–Catamarca border, at 6,882 m, higher than Ojos del Salado. In 2005 an Austrian team ran a differential GPS survey on the summit and found 6,793 m; an international expedition in 2006 found results around 6,800 m, and the 2007 joint survey gave 6,793 m. Pissis fell back to third, about 100 m below Ojos del Salado. The mountain is named after Pedro José Amadeo Pissis, a French geologist who worked for the Chilean government; it formed between 6.6 and 6.2 million years ago, and volcanism there ended about 2 million years ago, so it is classed as an extinct volcano.

Cerro Bonete, Mercedario and Walther Penck: satellites correct the record

Radar data from orbit has corrected other heights. Cerro Bonete in La Rioja was long quoted at 6,872 m; Shuttle Radar Topography Mission data shows it is about 6,759 m. Cerro Mercedario in San Juan is still given as 6,720 to 6,770 m, because SRTM suggests the commonly quoted 6,770 m is too high. For Walther Penck, also called Cazadero or Tipas, the official 6,658 m sits beside four digital elevation models giving 6,627 to 6,699 m and a 2013 handheld GPS reading of 6,688 m; analysts settle on about 6,670 m. Llullaillaco shows the same spread: the Andes list gives 6,739 m, while its own article says its height is most commonly given as 6,723 m, which still makes it the second-highest active volcano in the world.

What counts as a separate mountain: Huascarán Sur and Tres Cruces Sur

Height is only half of the method. A ranking also has to decide which summits are separate mountains and which are shoulders of a bigger one, and the usual tool is prominence. Wikipedia's "List of mountains in the Andes", the source for the table below, includes summits with at least 400 m of prominence and notes that the Andes hold about one hundred 6,000 m peaks and nearly 900 above 5,000 m.

Under that rule, Huascarán in Peru's Cordillera Blanca enters as one mountain, ranked by its southern summit, Huascarán Sur, at 6,768 m, the highest point in Peru and in all of Earth's tropics; its lower northern summit does not count separately. Its Quechua name Mataraju means "twin snow peaks". In the same way Nevado Tres Cruces is counted by Tres Cruces Sur, while Tres Cruces Centro (6,629 m) is left out as a subsidiary summit.

The top 10 of the Andes, by the List of mountains in the Andes

Two patterns stand out. Every mountain except Huascarán lies in Argentina or on its border with Chile, and seven of the ten are in the Puna de Atacama, a high volcanic plateau next to the Atacama Desert, one of the driest places on Earth. The same dry, cold air has preserved archaeology: on the summit of Llullaillaco, the highest archaeological site in the world, the mummified remains of three Inca children were found in 1999, and radiocarbon dating puts one child's death between 1430 and 1520 AD, centuries before the first recorded modern ascent in 1950.

The gaps are also tiny. With the heights clustered so tightly between 6,638 and 6,768 m, places four to ten could reshuffle with one more survey, which is why sources rarely agree on their exact order.

Chimborazo: highest by a different yardstick

One more measurement changes the answer completely. Earth bulges at the equator, so sea level there is several kilometres farther from the planet's centre than at the poles. Chimborazo, a stratovolcano in Ecuador just south of the equator, is only 6,263 m above sea level and ranks 39th in the Andes, yet its summit is the point on Earth's surface farthest from the centre, about 2,168 m farther out than the summit of Everest according to Wikipedia's Everest article.

So the honest answer depends on the yardstick: Aconcagua by height above sea level and by prominence, Ojos del Salado among volcanoes, and Chimborazo by distance from Earth's centre. The ways these figures are produced are set out in how mountains are measured, the wider range in our guide to the Andes, and the mountain itself in Aconcagua, the stone sentinel of the Andes.