Altiplano

The Altiplano (Spanish for high plain), in west-central South America, where the Andes are at their widest, is the most extensive area of high plateau on Earth outside of Tibet. Lake Titicaca is its best known geographical feature.

Location

The Altiplano is an area of inland drainage (endorheism) lying in the central Andes, occupying parts of Northern Chile and Argentina, Western Bolivia and Southern Peru. Its height averages about 3,750 meters (12,300 feet), slightly less than that of the Tibetan Plateau. Unlike conditions in Tibet, the Altiplano is dominated by massive active volcanoes of the Central Volcanic Zone to the west, such as Ampato (6288 m), Tutupaca (5816 m), Nevado Sajama  (6542 m), Parinacota (6348 m), Guallatiri (6071 m), Cerro Paroma (5728 m), Cerro Uturuncu (6008 m) and Licancabur (5916 m), and the Cordillera Real in the north east with Illampu (6368 m), Huayna Potosi (6088 m), Ancohuma (6427 m) and Illimani (6438 m). The Atacama Desert, one of the driest areas on the planet, lies southwest of Altiplano; to the east lies the humid Amazon Rainforest.

History

                                                          

At various times during the Pleistocene epoch, both the southern and northern Altiplano were covered by the vast pluvial lakes. Remnants are Lake Titicaca, straddling the Peru–Bolivia border, and Poopo, a salt lake that extends south of Oruro, Bovilia. Salar de Uyuni, locally known as Salar de Tunupa, and Salar Salar de Coipasa are two large dry salt flats formed after the Altiplano paleolakes and dried out.

Climatic zones

The term Altiplano is sometimes used to identify the altitude zone and the type of climate that prevails within it: it is colder than that of the tierra fria but not as cold as that of the tierra helada . Scientists classify the latter as commencing at an elevation of approximately 4,500 meters (or about 15,000 feet). Alternate names used in place of altiplano in this context include puna and páramos.

Climate

                                                     

In extentum, the climate is cool and semi-arid to arid, with mean annual temperatures that vary from 3°C near the western mountain range to 12°C near Lake Titicaca; and total annual rainfalls that range between less than 200 mm to the south west to more than 800 mm near and over Lake Titicaca. The diurnal cycle of temperature is very wide, with maximum temperatures in the order of 12 to 24°C and minimum in the order of -20 to 10°C. The coldest temperatures occur in the southwestern portion of the Altiplano during the months of June and July, which correspond to the Austral winter. The seasonal cycle of rainfall is marked, with the rainy season concentrating between December and March. The rest of the year tends to be very dry, cool, windy and sunny. Snowfall events may happen between April and September, especially to the north, but they are not very common (one to five events per year).


La Paz, Bolivia is the Altiplano's main city.

Geology

Several mechanisms have been suggested as responsible for the formation of the Altiplano plateau; theories try to explain why the topography in the Andes incorporates this large area of low relief at high altitude (high plateau) within the orogen:

1. Existence of weaknesses in the Earth's crust prior to tectonic shortening. Such weaknesses would cause the partition of tectonic deformation and uplift into the eastern and western cordillera, leaving the necessary space for the formation of the altiplano basin.
2. Magmatic processes rooted in the asthenosphere might have contributed to uplift the plateau.
3. Climate has controlled the spatial distribution of erosion and sediment deposition, controlling the lubrication along the Nazca Plate subduction and hence influencing the transmission of tectonic forces into South America.
4. Climate also determined the formation of internal drainage (endorheism) and sediment trapping within the Andes, potentially blocking tectonic deformation in the area between the two cordilleras.
5. Convective removal of dense lower lithosphere beneath the Altiplano caused that region to isostatically 'float' higher.