Expedition members pause at base camp to check and prepare their measurement instruments, including the Topcon HiPer+, before climbing Ojos del Salado.

In March 2007, a team of mountaineers and engineers set out to determine--within centimeter accuracy--the tallest mountain in the Americas and the tallest volcano in the world. The expedition was, in a sense, one of man versus nature.

The Andes Mountain Range in South America is more than 4,400 miles long and 300 miles wide in some parts. It extends from the top of the continent in Colombia through Ecuador, Bolivia and Perú, and serves as the geological border between Chile and Argentina. The popular tourist islands Aruba, Bonaire and Curaçao are actually the submerged peaks of the very northern end of the range. There is no “typical” mountain in the massive range, as it passes through every conceivable climate in the continent. Therefore, each contemplated climb presents its own challenges, as the courageous team found out. What’s more, the Andes is also known for its many volcanos, which range from extinct to very active.

With a burgeoning adventure tourism industry, a lot is at stake for the seven Andean countries in identifying and promoting its hot spots for visitors. The current hot spots for climbers are in Argentina, which claims the tallest mountain in the Western Hemisphere, and in Chile, home to the world’s tallest volcano. Or are they?

Every school-aged child in Argentina and Chile can tell you that the tallest mountain in the Western Hemisphere is El Aconcagua in Argentina and the tallest volcano in the world is Ojos del Salado in Chile. Despite what the textbooks include, there have been bitter disagreements over the titles of “tallest.” Chile has long claimed that Ojos del Salado may be taller than El Aconcagua; it is an idea supported by many mountaineers who have scaled both peaks. But in 1996, Argentina claimed that GPS data revealed that another volcano, their own volcano Monte Pissis, was taller than Ojos del Salado. This claim would make Argentina the holder of the two coveted altitude records.

The argument over which country has the tallest volcano is more than simple bantering between the two countries that are famous for disagreeing about everything from soccer scores to which region produces the best wine. Today the argument is less about cultural pride than it is about tourism--the industry that equals income for these regions that sorely need it. Avid mountaineers spend a lot of time and money traveling the world to climb the “tallest” of whatever it may be. Often they will spend weeks or months in-country preparing for an expedition. Second or third tallest just aren’t considered challenging enough to attract the climbers and the business that support them in large numbers. So, it is understandable that both Chile and Argentina would keep a close eye on altitude reports of the region’s volcanos and mountains; they are directly tied to their countries’ bottom lines.

There is little disagreement that El Aconcagua in the Mendoza Province of Argentina measures approximately 22,840 feet tall. The climb is very popular with adventure tourists and the peak’s height has been measured numerous times. The problem lies with wildly conflicting measurements of Ojos del Salado (in Atacama, Chile) and Monte Pissis (in La Rioja Province, Argentina). Is Ojos del Salado taller than El Aconcagua as some claim? Or is Ojos del Salado actually shorter than Monte Pissis?

The dispute was recently fueled in part by data gathered on the Shuttle Radar Topography Mission (SRTM) during the Endeavour’s flight STS-99 in February 2004. According to the SRTM, the reported heights of the three peaks were: El Aconcagua, 22,841 feet; Ojos del Salado, 22,608 feet; and Monte Pissis, 22,287 feet.

With the exception of El Aconcagua (where the measurement was close to the “accepted” height), the shuttle data did not match the official government records. Smoldering disagreements flamed. The reported margin of error of the SRTM for peaks at these altitudes is enough to cast doubt on the results, particularly considering that the onsite GPS measurement of Monte Pissis was claimed at 22,579 feet.

Hans Martin Schmitt, Pablo Kuntz and Sergio Suárez reach the Pissis Volcano peak and prepare to measure the coordinates of the volcano with a Topcon GB-500 at 6,791 meters above sea level.

The Climbers and Their Gear

With the support of Chilean Senator Baldo Prokurica in December 2006, an international team was assembled to scale and measure Ojos del Salado and Monte Pissis to settle the matter once and for all. The method chosen to measure the height of Ojos del Salado was dual-constellation signal reception from the U.S. GPS satellites and the Russian GLONASS system; the company chosen as the center of the mission and trusted for millimeter accuracy was Topcon (Livermore, Calif.). If the initial climb and measurements were successful, certain members of the team would then move on to climb Monte Pissis in Argentina.

The expedition to Ojos del Salado and Pissis was the brainchild of Phillip Reuter, owner of the adventure tourist agency Azimut 360 in Santiago, Chile. Reuter, a French national who resides in Chile, is well known for his mountaineering feats and high-altitude kayaking. Reuter assembled an international team around five goals: 1) to measure the exact altitude of Ojos del Salado; 2) to confirm or dismiss the idea that Ojos is taller than El Aconcagua; 3) to determine the identity and altitude of the tallest volcano in the world; 4) to render homage to famous mountaineer Rene’ Gajardo; and finally 5) to honor Pierre Aime’ Pissis, French cartographer, father of South American cartography. The team’s secondary mission was to deposit a plaque in Pissis’ memory at the summit of the mountain that bears his name.

In addition to Reuter, the team included guides Hans Martin Schmitt (Germany); Carlos Díaz and Sergio Juárez (Mexico); Pablo Kuntz from Azimut 360; Marc Turrel from Andes Magazine; Jean Claude Piessevaux, a Belgian-Chilean mountaineer and commercial engineer; Luis Alberto “Lama” Martinez of the Chilean outfitter company Lippi; tourist operator Atilio Bianchi; and at the center of the team, Omar López, the geological engineer for Topcon’s Chilean distributor Eduardo Pérez y Cía. López led the GPS training class and was in charge of all measurements on the expedition as well as technical support. Pérez y Cía provided the positioning instruments that were used to measure the summit: a HiPer+ geodetic receiver and a Topcon GB-500 receiver.

An expedition member checks the Topcon GB-500 configuration at the thermal lake Laguna Verde before the ascent.

A Grave Mission

Measuring mountains is not an easy business and each expedition has its particular problems. For Ojos the major problem is the extremely cold, dry air that whips up the mountain from the desert plain below. Due to this cold, the party members were vigilant in staying as warm as possible to diminish the risk of frost bite or, worse, hypothermia. Of more immediate concern, however, was the lack of moisture that can rapidly lead to dehydration and sudden death. “To go in seven days from sea level to six thousand meters is painful,” López told Andes Magazine. “The headaches are constant.”

On March 30 at 4:00, López started recording data with the HiPer+ receiver. At the final camp before the summit, he was capturing 10 satellite GPS and GLONASS signals and measured their altitude at 17,355.643 feet. The summit team needed to place the Topcon GB-500 at the summit of Ojos del Salado for approximately two hours to assure triangulation. While cold was a concern, López was confident the equipment would function properly; after all, he had previously measured 19 summits. However, the equipment had never been tested in such extreme temperatures.

While the summit team worried about the cold facing them at the top of the mountain, their main worry was more personal. Two hours seemed an impossibly long time to stay at that altitude almost fully exposed to the frigid, high winds. As the sole reason for the climb was to obtain the correct measurement, team members vowed to get the receiver in place.

On April 1, after acclimatizing to the altitude, the team began the final push for the top of Ojos del Salado. Several team members were suffering from altitude sickness including nausea and vomiting. Outside the tents, the winds were fierce, gusting as high as 75 mph. The cold was constant; the temperature had dropped to 30 degrees below zero overnight. On the final ascent, their water quickly froze in the insulated bottles.

Due to altitude sickness and fears of hypothermia, several members of the summit team turned back. The rest, including Schmitt, Reuter and Juárez pushed on. “This climb was much more difficult than previous expeditions to the Ojos,” Reuter was quoted as saying in Andes Magazine. It was the cold that made the difference: In the final push, with the wind chill factored in, the temperature felt like 50 or 60 degrees below zero. It was so cold that it would be impossible to remain at the summit for the two hours planned for proper triangulation with two other GPS+ base stations located at two nearby camps.

Even worse, the winds at the summit were so fierce that the receiver had to be jammed between several large rocks to avoid the worst of gusts. Everyone hoped the receiver would work--and work quickly. The team understood that, as Takushi Narumi, Latin America South regional manager for Topcon stated, “If it failed at the peak, the expedition would be dead.” In the end, the equipment worked--and faster than planned. In just 44 minutes the Topcon GB-500 triangulated with strong signals. Finally the operation was validated and the team could head for the relative warmth of camp; they had completed what they had set out to do.

Data from climbs earlier this year confirm that Argentina’s El Aconcagua is the highest mountain in the Western Hemisphere and Chile’s Ojos del Salado is the highest volcano in the world.

And the Tallest Is "¦

Using Topcon’s dual-frequency GPS+ GLONASS instruments, the team was ultimately able to determine the ellipsoid altitude of Ojos de Salado and, a few weeks later, Monte Pissis, along with their relative heights to Monte El Aconcagua. Ojos del Salado was found to be 22,615 feet and Pissis 22,280 feet. The data confirmed that Argentina’s El Aconcagua is the highest mountain in the Western Hemisphere and that Chile’s Ojos del Salado is the highest volcano in the world. Though earlier measurements were noted to not have been entirely accurate, the textbook declarations were correct.

Reuter was extremely pleased that the expedition had accomplished all of its goals in spite of the unexpected difficulties. Topcon’s Narumi stated that the result was “better than expected. Our equipment is rugged and reliable in the harshest areas of the world. The success of this expedition is a great achievement and displays the professionalism and courage of the expedition members.”

There might have been a bit of bragging on both sides of the border, but thanks to an international team of mountaineers, geological engineers and GPS technology, the dispute about the highest mountain in the Americas and the tallest volcano in the world has finally been settled.

Omar López of Topcon dealer Eduardo Pérez y Cía measures the position inside a camp tent to protect it against the 100km/h wind velocity. The team made a concrete marker.

Sidebar: Technical Data on the Measurements

The expedition to Monte Pissis, Argentina, was completed in April 2007. The following measurements are for the expeditions to Ojos del Salado as well as the GPS measurement of Monte Pissis and Monte El Aconcagua.

Ojos del Salado
Geoidal Undulation EGM96 = 140.997 ft
Geoidal Undulation South American = 140.420 ft 
Elipsoidal Height = 22,749.72 ft
Orthometric Height using the model EGM96 = 22,603.71 ft
Orthometric Height using the model SUDAM (SIRGAS) = 22,609.28 ft
Photogrammetric IGM = 22,613.85 ft

Monte Pissis
Geoidal Undulation EGM96 = 138.35 ft
Geoidal Undulation South American = 133.46 ft
Elipsoidal Height = 22,418.67 ft
Orthometric Height Using the Model EGM96 = 22,280.32 ft
Orthometric Height Using the Model SUDAM (SIRGAS) = 22,285.21 ft

Monte El Aconcagua (UDEC Expedition)
Official GPS Results Reported by the University of Concepción (Argentina)
Geoidal Undulation EGM96 = 105.31 ft
Geoidal Undulation South American = 103.51 ft
Elipsoidal Height = 22,949.90 ft
Orthometric Height Using the Model EGM96 = 22,844.39 ft
Orthometric Height Using the Model SUDAM = 22,846.39 ft