Ojos del Salado.

Nevado Ojos del Salado is a massive stratovolcano in the Andes on the Argentina–Chile border and the highest active volcano in the world at 6,893 m (22,615 ft). It is also the second highest mountain in the Western Hemisphere and Southern Hemisphere and the highest in Chile. It is located about 600 km (370 mi) north of Aconcagua, the highest mountain in the Western Hemisphere at 6,962 m (22,841 ft).

Due to its location near the Atacama Desert, the mountain has very dry conditions with snow usually only remaining on the peak during winter, though heavy storms can cover the surrounding area with a few feet of snow even in summer. Despite the generally dry conditions, there is a permanent crater lake about 100 m (330 ft) in diameter at an elevation of 6,390 m (20,960 ft) on the eastern side of the mountain. This is most likely the highest lake of any kind in the world.

The ascent of Ojos del Salado is mostly a hike except for the final section to the summit which is a difficult scramble that may require ropes. The first ascent was made in 1937 by Jan Alfred Szczepański and Justyn Wojsznis, members of a Polish expedition in the Andes.

Its name comes from the enormous deposits of salt that, in the form of lagoons or “eyes”, appear in its glaciers.

Elevation

The elevation of Ojos del Salado has been the subject of debate. A 2006 article in Andes Magazine offered that Ojos del Salado may be higher than Aconcagua, although the argument was premised on older, less accurate altitude surveys. The results of these older surveys assigned Ojos del Salado an elevation of 7,057 m (23,153 ft), which would have made it nearly 100 m (330 ft) higher than Aconcagua. As early as 1955, an estimate was made that the elevation of Ojos del Salado was 7,100 m (23,300 ft), but that was "simply  based on the altitude of the final camp, and the hours of ascent to the summit. In 1956 the first Chilean expedition led by the retired lieutenant René Gajardo measured the height of Ojos del Salado as 7,084 m (23,241 ft) with a pocket pressure altimeter. Apart from being an inexact method, the height shown by the altimeter was far too high as air pressure is generally lower in the afternoon, the time at which the team reached the summit.

Further expeditions to the area in the 80s and 90s provided evidence that nearby Monte Pissis was even higher than Ojos del Salado. Later measurements using more precise equipment, however, showed that Ojos del Salado is about 100 m (330 ft) higher than Pissis. Furthermore, in 2007 a Chilean–Argentine–European expedition organized by Andes Magazine and Azimut 360 performed a survey on both Ojos del Salado and Monte Pissis using more accurate instruments. It found the former to be 6,891 m (22,608 ft) and the latter 6,793 m (22,287 ft) Although this fits within recent handheld GPS surveys, which have estimated the mountain to be between 6,880 m (22,570 ft) and 6,910 m (22,670 ft), the vertical error margin of the expedition's equipment, 10 m (33 ft), leaves uncertainty as to the mountain's more precise altitude.

Ojos del Salado has two summits, one in Argentina and the other in Chile (the border between the two countries runs between the two summits). The difference in elevation of the two summits is less than 1 m (3 ft 3 in)

Volcanic Activity

There is no doubt that Ojos del Salado is a recently active volcano, but the question of whether it should be considered currently (or "historically") active is arguable. According to the Smithsonian Institution's Global Volcanism Program, the most recent known eruption was around 1300 years ago, with large error bars. However, there is also some evidence for a minor ash emission in 1993, which would definitely qualify the volcano as historically active. The presence of fumaroles high on the mountain and recent-looking lava flows, albeit of uncertain age, also argues in favor of a categorization as "active." By these definitions Ojos del Salado is the highest historically active volcano on earth. If the older date is accepted, the title of "highest historically active volcano" might reside instead with the somewhat lower Llullaillaco volcano, which certainly has erupted in historic times (most recently in 1877) and should still be considered active.