Andes

Geography glossary

Topic: World Physical Features and Natural Regions · NCERT: Beyond NCERT

Meaning

The Andes are the world's longest continental mountain range. They run for about 7,000 km down the western edge of South America. They are young fold mountains, formed where the Nazca Plate sinks under the South American Plate. They matter because they are the standard example of mountains built by subduction, and they shape the hazards, landforms and deserts of a whole continent.

Explanation

How the Andes formed (subduction)

  • Subduction means one plate sinks under another plate.
  • The setting:
  • The Nazca Plate is an ocean plate under the Pacific.
  • It moves towards the South American Plate, which is a land plate.

  • This is a convergent boundary (a place where two plates move towards each other).

  • The process:

  • Ocean rock is heavier (denser) than land rock, so the Nazca Plate sinks underneath.
  • The edge of the land plate gets squeezed. Its rock layers fold and push upward.

  • The crust thickens and rises, and this builds the Andes.

  • Volcanoes as a by-product:

  • The sinking plate melts deep below the surface.
  • The molten rock (magma) rises up through the crust.
  • This forms a chain of volcanoes along the range.

Type and belt

  • The Andes are young fold mountains. They are tall, have sharp peaks and are still rising, because erosion has not yet worn them down.
  • They belong to the Circum-Pacific belt ("Ring of Fire" mountains). Here, ocean plates slide under land plates all around the Pacific.
  • The Rockies of North America are the other main range in this belt.

Main parts and features

  • Altiplano ("high plain"):
  • A high, flat basin between two Andean ridges, mainly in Bolivia and Peru.
  • It is an intermontane plateau (a plateau with mountains all around it).

  • It holds Lake Titicaca, on the Peru–Bolivia border.

  • Aconcagua (about 6,961 m, Argentina):

  • The highest peak of the Andes and of the Americas.
  • The highest peak in the world outside Asia.

Effect on climate

  • The Andes stand across the path of the winds and block them.
  • West side: this helps keep the Atacama Desert (Chile) very dry. The cold Peru (Humboldt) ocean current off the coast adds to the dryness.
  • East side: Patagonia (Argentina) lies in the rain shadow (the dry side of a mountain, away from the moist wind). So it is a dry plateau.

Where it occurs

  • Continent: the western edge of South America, along the Pacific coast.
  • Seven countries (north → south): Venezuela, Colombia, Ecuador, Peru, Bolivia, Chile, Argentina.
  • Named places:
  • Aconcagua: Argentina, the highest peak.
  • Altiplano: mainly Bolivia and Peru.
  • Lake Titicaca: Peru–Bolivia border, on the Altiplano.
  • Atacama Desert: Chile, on the western side.

  • Patagonia: Argentina, on the eastern (rain-shadow) side. It is a piedmont plateau (a plateau at the foot of mountains, on one side).

  • India link: India has no part of the Andes. India's own young fold range, the Himalaya, formed in a different way. There, the Indian Plate hit the Eurasian Plate about 50 million years ago, so land met land, and not ocean against land [1].

Don't confuse with

  • Himalaya: both are young fold mountains. But the Himalaya formed from a land plate hitting a land plate (Indian into Eurasian) in the Alpine-Himalayan belt. The Andes formed from an ocean plate subducting under a land plate in the Circum-Pacific belt.
  • Rockies: these are in the same Circum-Pacific belt, but in North America (western Canada and the USA). The Rockies form the continental divide of North America. The Andes are the longest continental range.
  • Old fold mountains (Urals, Appalachians, Aravallis, Great Dividing Range): these are low and rounded after long erosion. The Andes are young: tall, sharp-peaked and still rising.
  • Altiplano vs Patagonia: the Altiplano is an intermontane plateau, with mountains on all sides (Bolivia–Peru). Patagonia is a piedmont plateau in the rain shadow, on one side of the Andes (Argentina).

Prelims Hooks

  • The Andes are about 7,000 km long. They are the world's longest continental mountain range.
  • Formation: the Nazca Plate subducts under the South American Plate. This is ocean plate under land plate, and it explains the chain of volcanoes.
  • Highest peak: Aconcagua (about 6,961 m) is in Argentina, not Chile. It is the highest peak in the Americas and the highest outside Asia.
  • Seven Andean countries: Venezuela, Colombia, Ecuador, Peru, Bolivia, Chile, Argentina. Brazil is not one of them (a common trap).
  • Lake Titicaca lies on the Altiplano, on the Peru–Bolivia border. The Bolivian Altiplano is an intermontane plateau.
  • Old vs young trap: the Andes, Rockies, Atlas and Zagros are young fold mountains. The Urals, Appalachians and Aravallis are old.

Mains Points

  • Plate tectonics and hazards (GS-I/III):
  • The Andes lie on a convergent plate boundary in the Ring of Fire.
  • So the region faces earthquakes, landslides and volcanic eruptions.

  • Responses include earthquake-safe buildings, careful planning of dams and roads, and early-warning systems.

  • Relief controls climate (GS-I):

  • The Andes block the winds and create contrasts across the continent.
  • The Atacama in the west is very dry. Patagonia in the east is a rain-shadow desert.

  • This is a good example of how mountains decide where rain falls and where deserts form.

  • Landforms built by one process (GS-I):

  • One subduction process has built several landforms together.
  • These are the fold ranges, a volcanic chain, a high intermontane plateau (the Altiplano, with Lake Titicaca) and a piedmont plateau (Patagonia).
  • So the Andes work as a model case study for answers on convergent boundaries.

Related concepts

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Sources

  1. 1USGS, "Understanding plate motions" (This Dynamic Earth)pubs.usgs.gov · tier 2