Andes

• 1. Introduction

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  The Andes stretch 8900 km down the western edge of South America, the longest continental mountain range on Earth, and the highest outside Asia. At their widest, between 18 degrees S and 20 degrees S latitude, they span 200-700 km, with an average height of about 4000 m. Argentina's Aconcagua, the range's tallest peak, rises to roughly 6961 m, yet the strangest superlative belongs to a lower mountain: the summit of Chimborazo in Ecuador sits farther from the center of the Earth than any other point on the planet's surface, a quirk of the equatorial bulge caused by the planet's own rotation. The range also hosts the world's highest volcanoes, among them Ojos del Salado on the Chile-Argentina border, which climbs to 6893 m. Running through seven countries, Argentina, Chile, Bolivia, Peru, Ecuador, Colombia and Venezuela, the Andes form the western backbone of a much longer chain, the American Cordillera, that continues into the mountains of Antarctica. Beneath that unbroken skyline lies a story of colliding continents, buried metal, vanished empires and creatures found nowhere else on Earth.

• 2. Naming And Divisions

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  Most linguists trace the name Andes to the Quechua word anti, meaning east, the root behind Antisuyu, the eastern quarter of the Inca Empire. A rival theory points instead to anta, the Aymara word for copper. The related term cordillera, used for individual stretches of the range as well as the whole chain, comes from the Spanish cordel, meaning rope.

  Geographers split the range into three broad sections: the Southern Andes of Argentina and Chile, south of the peak Llullaillaco; the Central Andes of Bolivia and Peru; and the Northern Andes of Colombia, Ecuador and Venezuela, themselves divided into three branches. At the range's northern tip, the separate Sierra Nevada de Santa Marta is often counted as part of the Northern Andes. Between the ranges sit high plateaus, including the Altiplano, the second-highest plateau on Earth after Tibet's, home to cities such as La Paz, Sucre, El Alto, Arequipa and Bogotá. Climatically, the whole system is grouped into the Tropical Andes, the Dry Andes and the Wet Andes. Other giants of the range include Huascarán in Peru, at 6768 m, and Illimani in Bolivia, at 6438 m. Off the coast of Venezuela, the Leeward Antilles islands of Aruba, Bonaire and Curaçao were once assumed to be the drowned northern tip of the range, though ongoing geological study now points to a far more complex tectonic boundary between the South American and Caribbean plates.

• 3. A Range Still Rising

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  Where the Nazca Plate dives beneath the South American Plate, the collision has folded and lifted the crust for tens of millions of years, since the Mesozoic and Tertiary eras, building the Andes as part of the Pacific Ring of Fire. The range only took its present shape during the Cretaceous Period, when older sedimentary and metamorphic rock was uplifted, faulted and folded above the ancient cratons to the east. Climate then fed back into geology: as the rising Andes cast a rain shadow over Chile, the resulting aridity starved the coastal subduction zone of sediment, which in turn sped up the uplift along the coast. To the east, the range is bounded by sedimentary basins, among them the Orinoco, Amazon, Madre de Dios and Gran Chaco basins, separating it from the ancient cratons of eastern South America; across the 1000 km Drake Passage to the south, the mountains of the Antarctic Peninsula appear to be a continuation of the same chain.

  At the Arica Elbow, near 18 degrees S, the coastline and the Andes both bend sharply, part of what geologists call the Bolivian Orocline, where segments of the range have rotated 15 degrees counter-clockwise to the north and 20 degrees clockwise to the south. Further south lie two subtler bends, the Maipo Orocline between 30 degrees S and 38 degrees S and the Patagonian Orocline near the range's southern tip.

  The 1960 Valdivia earthquake, at magnitude 9.5, remains, as of 2024, the strongest ever recorded on a seismometer, produced by the same subduction zone that built the mountains above it. The same zone has since generated the magnitude-8.8 Maule earthquake in 2010 and the magnitude-8.2 Illapel earthquake in 2015, while the most powerful earthquake ever generated within the plate itself, rather than at its boundary, struck Peru in 1947 at magnitude 7.5. Volcanoes track the same subduction line, clustered into four active zones separated by long stretches of quiet. Seismic behavior itself varies with the plumbing of the subduction zone: research has found that more hydrated mantle material tends to produce more frequent but lower-magnitude earthquakes, while drier, dehydrated zones carry a higher risk of a single larger one. The highest rate of seismic activity of all is recorded between 33 degrees S and 35 degrees S, where the subducting plate runs almost horizontal beneath the surface.

• 4. Riches Underground

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  Chile and Peru rank as the world's first and second largest copper exporters, both drawing on porphyry copper deposits that formed in the forelands of the Atacama Desert, where hydrothermal fluids cooled around ancient plutons and volcanic systems undisturbed by the region's dry climate. That same aridity produced two very different resources: vast saltpeter deposits, mined heavily until synthetic nitrates replaced them, and the salt flats of Atacama and Uyuni, the former the world's largest source of lithium and the latter its largest reserve of the element outright. Argentina, Bolivia and Chile between them hold the three biggest lithium reserves on the planet. In Bolivia's Cordillera Central, meanwhile, Mesozoic and Neogene plutonism built the Bolivian tin belt alongside the now largely depleted silver deposits of Cerro Rico de Potosí. Along the Argentina-Chile border, the gold deposits of the El Indio Gold Belt lie next to or below glaciers, raising cross-border questions about mining's impact on the ice itself.

  Andean peoples shaped gold into ceremonial jewelry long before the Spanish arrival, when large-scale mining began in earnest, centered on Potosí in present-day Bolivia and Cerro de Pasco in Peru, among the principal mines of the Spanish Empire in the Americas; the Río de la Plata and Argentina itself take their names from Potosí silver. Mining never stopped: Peru's Yanacocha ranks as the fourth-largest goldmine in the world, and the porphyry copper deposits of Chuquicamata and Escondida in Chile and Toquepala in Peru now sit alongside the old Potosí silver workings as landmarks of the same five-century-old industry.

• 5. Climate And Life

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  Snow lines trace the length of the Andes like a signature of latitude: as low as 300 m in Tierra del Fuego at 55 degrees S, they climb to 2000 m at 40 degrees S, 4500 m on Aconcagua at 32 degrees S, and as high as 4800-5200 m in the drier mountains of southern Peru and northern Chile. In Colombia, the northern Andes stay rainy and warm, averaging 18 C, and rainforest can grow just kilometers from the snow-covered summit of Cotopaxi.

  That range of conditions has produced roughly 30,000 species of vascular plant, about half of them found nowhere else, a density of endemism that outstrips any other hotspot on Earth. Among them is Cinchona pubescens, the tree that yields quinine, the malaria treatment, found as far south as Bolivia; the Andes are also the ancestral home of both tobacco and the potato. At altitudes up to 4500 m grow Polylepis forests, known locally by names like Queñua and Yagual, now considered highly endangered, with some estimates putting as little as 10 percent of the original woodland still standing.

  The Andes hold almost 1,000 species of amphibian, two-thirds of them endemic, making the range the single most important region on the planet for the group. Nearly 600 mammal species live there alongside more than 1,700 kinds of bird and over 600 reptiles. On the Altiplano, wild vicuña and guanaco graze near their domesticated relatives, the llama and alpaca, while dawn-and-dusk-active chinchillas, two threatened rodent species, shelter in the same high alpine ground. The Andean condor, the largest bird of its kind in the Western Hemisphere, soars in low numbers across much of the range, sharing the open highlands with the Andean goose, the giant coot, flamingos drawn to hypersaline lakes and the lesser rhea. Lake Titicaca alone shelters the highly endangered Titicaca flightless grebe and Titicaca water frog, and the humid cloud forests further north hold three of the range's few large mammals: the threatened mountain tapir, the spectacled bear and the yellow-tailed woolly monkey. Those same forests, spanning Colombia, Ecuador, Peru, Bolivia and far northwestern Argentina, are home to mountain toucans, quetzals and the Andean cock-of-the-rock, alongside mixed flocks of tanagers that contrast with the cryptic, mostly unseen wrens, tapaculos and antpittas calling from the undergrowth.

• 6. Empires And Conquest

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  By the 15th century, centuries of agricultural development among Andean hunter-gatherers had culminated in the Inca Empire, built through a mix of imperialistic militarism and meticulous administration. The Inca state sponsored aqueducts and roads, some of which still stand today.

  Weakened by European diseases and internal civil war, the Inca Empire fell in 1532 to Francisco Pizarro's army of just 180 Spaniards, reinforced by tens of thousands of warriors from peoples the Incas had themselves subjugated, including the Huancas, Chachapoyas and Cañaris. Not every Inca stronghold was found: Machu Picchu, perched where the eastern Andes descend toward the Amazon, escaped Spanish discovery entirely. Quechua and Aymara remain the main surviving languages of the Andean peoples who outlasted that conquest. Spanish rule pushed deeper into the mountains chasing mining wealth, and it held until the 19th century, when a wave of anti-imperialist rebellion swept the region and broke Spanish colonial rule into five independent Andean states. Even after independence, the range remained only partly mapped: the surveyors Woodbine Parish and Joseph Barclay Pentland charted a large part of the Bolivian Andes as late as 1826 and 1827.

• 7. Cities, Roads And Farms

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  La Paz sits at roughly 3650 m, the highest seat of government in the world, and parts of its sprawl, including the city of El Alto, climb even further to 4200 m. Bogotá, with a metropolitan population above ten million, is the largest city in the range itself, while Lima, on the coast just outside the Andes proper, is the largest city of any Andean country and seat of the Andean Community of Nations.

  The Paso Internacional Los Libertadores still carries the main crossing between Argentina and Chile, one of the few links across terrain that has always made roads and railways costly to build; only one railroad links Chile to Peru across the range. Bolivia built several of its Andean highways during its war with Paraguay, moving troops and supplies to a lowland front. Chile once claimed land on the Andes' eastern side too, ceding those claims around 1870 in a diplomatic deal struck during the War of the Pacific against an allied Bolivia and Peru; Bolivia has been landlocked ever since and, with diplomatic relations with Chile suspended since 1978, ships most of its trade through ports in Argentina and Uruguay.

  Andean farmers have irrigated these slopes for more than 6,000 years, and terracing spread widely once the Inca Empire began expanding its territory. The potato remains a staple crop grown for local consumption, while maize has long been used to brew chicha. Modern export crops include tobacco, cotton, quinoa and coffee, alongside coca, still grown legally in some countries for a mild herbal tea and illegally elsewhere as the raw material for cocaine.