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The Andes

Introduction

The Andes Mountains, the longest continental mountain range in the world, extend over 8,900 kilometers (5,530 miles) along the western coast of South America. They traverse seven countries: Argentina, Chile, Bolivia, Peru, Ecuador, Colombia, and Venezuela. This vast range varies in width from 200 to 700 kilometers (124 to 435 miles) and averages around 4,000 meters (13,123 feet) in elevation. Rather than a single unbroken line, the Andes consist of a complex system of parallel and transverse ranges, known as cordilleras, interspersed with high plateaus and valleys. Among these, the Altiplano Plateau stands out as the second highest plateau globally, after the Tibetan Plateau. The Andes' diverse environmental conditions reflect the range's span across different latitudes. Notably, the Andes include some of the highest peaks outside Asia, such as Aconcagua in Argentina, which reaches 6,961 meters (22,838 feet) and is the tallest peak in the Western Hemisphere. Additionally, the range hosts the world's highest volcanoes, like Ojos del Salado on the Chile-Argentina border, which rises to 6,893 meters (22,615 feet). The Andes significantly influence South America's geography, climate, and ecosystems, acting as a natural barrier between the continent's narrow coastal regions and its vast interior.

Formation

The Andes were formed through complex tectonic processes that began around 250 million years ago during the breakup of the supercontinent Pangaea. As Pangaea fragmented, its southern portion, Gondwana, split into landmasses that would become the present-day continents. The collision between the oceanic Nazca Plate and the continental South American Plate was crucial to the Andes' formation. This collision caused the Nazca Plate to subduct beneath the South American Plate, triggering intense mountain-building activity. This tectonic convergence began in the Mesozoic Era and intensified throughout the Cenozoic Era, which spans the last 65 million years. The uplift, faulting, and folding of sedimentary and metamorphic rocks along South America's western edge resulted from this prolonged activity. Around 170 million years ago, as the Atlantic Ocean opened to the east, the Nazca Plate began subducting beneath the South American Plate. This not only caused significant uplift but also led to volcanic activity along the plate boundary. The intrusion of magma from the Earth's mantle formed a volcanic arc, and the injection of hot solutions into surrounding continental rocks created mineral-rich dikes and veins. The Andes' current form, with dramatic vertical relief of over 40,000 feet between the Peru-Chile Trench and the Andean peaks, emerged from ongoing tectonic forces. Regional variations in tectonic stress, erosion, and uplift have created a diverse geological landscape. Notable features, such as the Bolivian Orocline—a pronounced bend in the range—resulted from crustal shortening and the rotation of Andean segments.

Seismic and volcanic activity

The tectonic forces that formed the Andes also contribute to its high seismic and volcanic activity. The subduction of the Nazca and Antarctic Plates beneath the South American Plate generates frequent earthquakes and volcanic eruptions along the western coast of South America. Significant earthquakes, like the 1960 Valdivia earthquake (magnitude 9.5), have occurred here. Seismic activity varies along the subduction zone due to factors such as the angle of subduction, friction between plates, and the hydration levels of mantle materials. Volcanism in the Andes is complex, with active volcanoes distributed across four distinct volcanic zones separated by inactive regions. The Andean volcanic belt’s shape reflects the diverse tectonic settings it traverses, including rift systems, extensional zones, and transpressional faults.

Geography

The Andes can be broadly divided into three main sections: the Southern, Central, and Northern Andes. Each of these sections spans several countries in South America and possesses unique geological and topographical characteristics. The Southern Andes, encompassing parts of Argentina and Chile, begin south of the Llullaillaco volcano and include the Patagonian, Fuegian, and Chilean cordilleras. In the far south, the Fuegian Andes start on the eastern edge of Tierra del Fuego, with peaks like Mounts Darwin and Valdivieso reaching heights under 7,900 feet. The Patagonian Andes rise north of the Strait of Magellan, featuring rugged landscapes with glaciers, fjords, and forests, particularly in Chile. Mount Fitz Roy (11,073 feet) is one of the highest points here. As the range progresses northward, it broadens, becomes drier, and rises in elevation, transitioning into the Central Andes. The Central Andes cover regions of Chile, Argentina, Bolivia, and Peru. This section is characterized by a drier climate, higher elevations, and a broader range. It serves as a natural divide between rivers flowing into the Pacific and Atlantic Oceans. Prominent peaks like Mount Aconcagua (22,841 feet), the highest in the Andes, and vast plateaus such as the Altiplano, define this region. The Altiplano hosts salt flats, volcanoes, and Lake Titicaca, the world's highest navigable lake. As the Andes extend into Peru, they split into several ranges, with deep gorges and high peaks like Mount Huascarán (22,205 feet) dominating the landscape. The Northern Andes begin in Ecuador and extend through Colombia and Venezuela. The transition from the Central to the Northern Andes is marked by the Loja Knot in southern Ecuador. In this region, the Andes consist of two main chains, the Cordillera Occidental and Cordillera Central, separated by a central plateau filled with volcanoes. Northward in Colombia, the Andes split into three distinct ranges: the Occidental, Central, and Oriental cordilleras. These ranges are separated by deep valleys, with the Cordillera Central containing active volcanoes and the Cordillera Oriental hosting vast upland basins like the Sabanas, where Bogotá is located. As the Andes continue into Venezuela, the Cordillera de Mérida stretches northeastward, forming snow-covered peaks that separate the Caribbean and the Orinoco River basin.

Climate

The climate of the Andes varies widely due to factors like latitude, altitude, and proximity to the sea. In the southern Andes, the climate is cool and rainy, while the central Andes are dry, and the northern Andes, particularly in Colombia, are warm and wet. These conditions can change dramatically over short distances, with rainforests and snow-capped peaks sometimes situated close to each other. The snow line varies significantly, from around 4,500 meters in northern regions to lower elevations in the southern Andes. In Chile and Argentina, the Andes are categorized into Dry and Wet zones. The Dry Andes, extending from the Atacama Desert to the Maule River, experience irregular precipitation and significant temperature fluctuations. Rock glaciers are more common here due to intense solar radiation, while higher altitudes receive more precipitation. Temperature trends generally increase from south to north, but local factors cause considerable variation. The western slopes are drier, influenced by the Pacific Ocean, while the eastern slopes receive more rain from the Amazon. In the Peruvian and Ecuadorian Andes, temperatures range from tropical at lower elevations to polar at the highest peaks. Between 4,900 and 8,200 feet, the climate is tropical to subtropical, while above 11,500 feet, temperatures drop, reaching subfreezing conditions and polar climates at the highest elevations. This variation in temperature and precipitation across the Andes contributes to a wide range of microclimates, particularly in Peru, leading to diverse ecological habitats.

Ecology

The Andes Mountains extend from the tropical rainforests of northern Venezuela to the icy plains of southern Chile and Argentina, crossing through the arid Atacama Desert. Once enveloped by lush rainforests and tropical dry forests, the northern Andes have seen a significant decline in these habitats, particularly in Colombia. In contrast, the western Andes of Peru, Chile, and Argentina are drier, with vegetation consisting of deciduous woodlands and xeric shrubs. This vast mountain range is home to around 30,000 vascular plant species, half of which are endemic, showcasing an impressive array of biodiversity. Notable plants include the Cinchona pubescens, which produces quinine for treating malaria, and important crops like potatoes and tobacco. The high-altitude Polylepis forests, found across several Andean countries, are critically endangered due to deforestation. The animal life in the Andes is equally remarkable, with about 1,000 amphibian species, two-thirds of which are endemic. The region is vital for mammal diversity, boasting around 600 species, and for bird life, with over 1,700 species, one-third of them endemic. Iconic animals such as the vicuña, guanaco, and Andean condor inhabit the Andes. The fauna varies with altitude, with species adapted to extreme heights. The Andes' diverse environment, shaped by altitude and climate, supports distinct plant and animal communities.

People and resources

Human presence in the Andes dates back around 10,000 to 12,000 years, with permanent habitation occurring at up to 17,100 feet and temporary work at 19,000 feet. In the southern Andes, population density is low, with small communities of shepherds and farmers. In contrast, the northern Andes, especially from Bolivia to Colombia, are densely populated, with many living above 10,000 feet. The Quechua and Aymara Indigenous peoples in Bolivia and Peru play central roles in agriculture and animal husbandry, while various Indigenous and mestizo groups in Ecuador and Colombia are involved in farming and local industries. The Andes are a treasure trove of valuable minerals, including copper, tin, and lithium, which significantly impact the economies of countries like Chile and Peru. The Atacama Desert's dry climate has preserved these deposits, making them easier to exploit. Additionally, the region is rich in hydrocarbons, with certain eastern fold and thrust belts trapping commercially viable oil and gas. The Andes' geological history, including magma intrusion and mineral-rich veins, makes it one of the world’s most resource-rich regions. Agriculture is challenging due to the harsh terrain and unpredictable weather, leading to low crop yields. Traditional terracing and irrigation practices support staple crops like potatoes and maize, as well as cash crops like coffee and tobacco.

Test your knowledge

Which country is home to the highest peak in the Andes?

3

Which tectonic plates are involved in the formation of the Andes Mountains?

2

What is the highest navigable lake in the world, located in the Andes?

1

What notable feature is found in the Andes Mountains?

1

In which region of the Andes is the climate typically warm and wet?

3

References

Britannica

Wikipedia