Andes
The Andes, Andes Mountains or Andean Mountain Range are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long and wide and has an average height of about. The Andes extend from south to north through seven South American countries: Argentina, Chile, Bolivia, Peru, Ecuador, Colombia, and Venezuela.
Along their length, the Andes are split into several ranges, separated by intermediate depressions. The Andes are the location of several high plateaus—some of which host major cities such as Arequipa, Bogotá, Cali, Medellín, El Alto, La Paz, Mérida, Santiago and Sucre. The Altiplano Plateau is the world's second highest after the Tibetan Plateau. These ranges are in turn grouped into three major divisions based on climate: the Tropical Andes, the Dry Andes, and the Wet Andes.
The Andes are the highest mountain range outside of Asia. The range's highest peak, Argentina's Aconcagua, rises to an elevation of about above sea level. The peak of Chimborazo in the Ecuadorian Andes is farther from the Earth's center than any other location on the Earth's surface, due to the equatorial bulge resulting from the Earth's rotation. The world's highest volcanoes are in the Andes, including Ojos del Salado on the Chile–Argentina border, which rises to.
The Andes are also part of the American Cordillera, a chain of mountain ranges that consists of an almost continuous sequence of mountain ranges that form the western "backbone" of the Americas and Antarctica.
Etymology
The etymology of the word Andes has been debated. The majority consensus is that it derives from the Quechua word anti "east" as in Antisuyu, one of the four regions of the Inca Empire. Others suggest that it is in fact from the word anta of the older Aymara language.The term cordillera comes from the Spanish word cordel "rope" and is used as a descriptive name for several contiguous sections of the Andes, as well as the entire Andean range, and the combined mountain chain along the western part of the North and South American continents.
Geography
The Andes mountain range, the longest continental mountain system in the world, extends approximately along the western edge of South America, spanning seven countries. Its width varies from to, encompassing a series of parallel cordilleras, high plateaus, and deep intermontane valleys. Prominent peaks such as Aconcagua at in Argentina, Huascarán at in Peru, and Illimani in Bolivia illustrate the extreme elevations and rugged relief that define the range.The Andes encompass a wide variety of climatic and ecological zones, ranging from humid cloud forests on the eastern slopes to the arid high plains of the Altiplano and the glaciated summits of the southern Andes. These sharp environmental gradients have strongly influenced human settlement and the development of major highland cities such as Bogotá, Cusco, La Paz and Quito.
The Andes can be divided into three sections:
- The Southern Andes in Argentina and Chile, south of Llullaillaco;
- The Central Andes in Bolivia and Peru; and
- The Northern Andes in Colombia, Ecuador, and Venezuela. The northern Andes are separated into three branches.
The Leeward Antilles islands Aruba, Bonaire, and Curaçao, which lie in the Caribbean Sea off the coast of Venezuela, were formerly thought to represent the submerged peaks of the extreme northern edge of the Andes range, but ongoing geological studies indicate that such a simplification does not do justice to the complex tectonic boundary between the South American and Caribbean plates.
Geology
The Andes are an orogenic belt of mountains along the Pacific Ring of Fire, a zone of volcanic activity that encompasses the Pacific rim of the Americas as well as the Asia-Pacific region. The Andes are the result of tectonic plate processes extending during the Mesozoic and Tertiary eras, caused by the subduction of oceanic crust beneath the South American Plate as the Nazca Plate and South American Plate converge. These processes were accelerated by the effects of climate. As the uplift of the Andes created a rain shadow on the western fringes of Chile, ocean currents and prevailing winds carried moisture away from the Chilean coast. This caused some areas of the subduction zone to be sediment-starved, which in turn prevented the subducting plate from having a well lubricated surface. These factors increased the rate of contractional coastal uplift in the Andes. The main cause of the rise of the Andes is the contraction of the western rim of the South American Plate due to the subduction of the Nazca Plate and the Antarctic Plate. To the east, the Andes range is bounded by several sedimentary basins, such as the Orinoco Basin, the Amazon Basin, the Madre de Dios Basin, and the Gran Chaco, that separate the Andes from the ancient cratons in eastern South America. In the south, the Andes share a long boundary with the former Patagonia Terrane. To the west, the Andes end at the Pacific Ocean, although the Peru–Chile Trench can be considered their ultimate western limit. File:Cono de Arita, Salta..jpg|thumb|"Cono de Arita" in the Puna de Atacama, Salta |leftThe Andean orogen has a series of bends or oroclines. The Bolivian Orocline is a seaward-concave bending in the coast of South America and the Andes Mountains at about 18° S. At this point, the orientation of the Andes turns from northwest in Peru to south in Chile and Argentina. The Andean segments north and south of the Orocline have been rotated 15° counter-clockwise to 20° clockwise respectively. The Bolivian Orocline area overlaps with the area of the maximum width of the Altiplano Plateau, and according to Isacks the Orocline is related to crustal shortening. The specific point at 18° S where the coastline bends is known as the Arica Elbow. Further south lies the Maipo Orocline, a more subtle orocline between 30° S and 38°S with a seaward-concave break in the trend at 33° S. Near the southern tip of the Andes lies the Patagonian Orocline.Orogeny
The western rim of the South American Plate has been the place of several pre-Andean orogenies since at least the late Proterozoic and early Paleozoic, when several terranes and microcontinents collided and amalgamated with the ancient cratons of eastern South America, by then the South American part of Gondwana.The formation of the modern Andes began with the events of the Triassic, when Pangaea began the breakup that resulted in developing several rifts. The development continued through the Jurassic Period. It was during the Cretaceous Period that the Andes began to take their present form, by the uplifting, faulting, and folding of sedimentary and metamorphic rocks of the ancient cratons to the east. The rise of the Andes has not been constant, as different regions have had different degrees of tectonic stress, uplift, and erosion.
Across the Drake Passage lie the mountains of the Antarctic Peninsula south of the Scotia Plate, which appear to be a continuation of the Andes chain.
The far east regions of the Andes experience a series of changes resulting from the Andean orogeny. Parts of the Sunsás Orogen in Amazonian craton disappeared from the surface of the earth, being overridden by the Andes. The Sierras de Córdoba, where the effects of the ancient Pampean orogeny can be observed, owe their modern uplift and relief to the Andean orogeny in the Tertiary. Further south in southern Patagonia, the onset of the Andean orogeny caused the Magallanes Basin to evolve from being an extensional back-arc basin in the Mesozoic to being a contractional foreland basin in the Cenozoic.
Seismic activity
Tectonic forces above the subduction zone along the entire west coast of South America where the Nazca Plate and a part of the Antarctic Plate are sliding beneath the South American Plate continue to produce an ongoing orogenic event resulting in minor to major earthquakes and volcanic eruptions to this day. Many high-magnitude earthquakes have been recorded in the region, such as the 2010 Maule earthquake, the 2015 Illapel earthquake, and the 1960 Valdivia earthquake, which as of 2024 was the strongest ever recorded on seismometers.The amount, magnitude, and type of seismic activity varies greatly along the subduction zone. These differences are due to a wide range of factors, including friction between the plates, angle of subduction, buoyancy of the subducting plate, rate of subduction, and hydration value of the mantle material. The highest rate of seismic activity is observed in the central portion of the boundary, between 33°S and 35°S. In this area, the angle of subduction is very low, meaning the subducting plate is nearly horizontal. Studies of mantle hydration across the subduction zone have shown a correlation between increased material hydration and lower-magnitude, more frequent seismic activity. Zones exhibiting dehydration instead are thought to have a higher potential for larger, high-magnitude earthquakes in the future.
The mountain range is also a source of shallow intraplate earthquakes within the South American Plate. The largest such earthquake struck Peru in 1947 and measured 7.5. In the Peruvian Andes, these earthquakes display normal, strike-slip, and reverse mechanisms. The Amazonian Craton is actively underthrusted beneath the sub-Andes region of Peru, producing thrust faults. In Colombia, Ecuador, and Peru, thrust faulting occurs along the sub-Andes due in response to contraction brought on by subduction, while in the high Andes, normal faulting occurs in response to gravitational forces.
In the extreme south, a major transform fault separates Tierra del Fuego from the small Scotia Plate.