Read down for an insight into the geology and landscape of Argentina.
Argentina is the second largest country in South America in area, extending across the continent some 1580 km from east to west and 3460 km from north to south. Its northernmost point is at latitude 22°S, that is just within the tropics; at Tierra del Fuego and Isla de los Estados it extends south of 54°S, the latitude of Scotland or Labrador. The coast of this territory, extending over 2000 km, runs wholly along the Atlantic apart from the north coast of the Beagle Channel which links the Atlantic and the Pacific. The western border with Chile follows the crest of the Andes, but below 46°S, the drainage is complex and border disputes have arisen ever since the Treaty of 1881 between the two countries established the principle that the border should follow the watershed.
Together with Brazil, Paraguay and Uruguay, Argentina is the visible part of the South American Plate which has been moving for the past 125 million years away from its former union with Africa. The submerged part of this plate forms a broad continental shelf under the Atlantic Ocean; in the south this extends over 1000 km east and includes the Falkland Islands/ Islas Malvinas. Since the 'break' between the plates, there have been numerous invasions and withdrawals of the sea over this part of the South American continent, but the Andean mountain building from the end of the Cretaceous (65 million years ago) to the present day dominates the surface geology. Of the many climatic fluctuations, the Pleistocene Ice Age up to 10,000 BC has done most to mould the current landscape. At its maximum, ice covered all the land over 2,000 m and most of Patagonia. In the mountains, ice created virtually all the present day lakes and moraine deposits can be found everywhere. However, the special feature of the heartland of Argentina is the fine soil of the Pampas, the result of ice and water erosion and the unique wind systems of the southern cone of the continent.
The Northwest
Northern and western Argentina are dominated by the satellite ranges of the Andes. Between the
mountains of the far northwest is the puna, a high plateau rising to 3400-4000 m, on which are
situated salt flats or salares, some of which are of interest for their wildlife. East of this
is the pre-puna, the gorges and slopes ranging in altitude from 1700 m to 3400 m which connect
the puna with the plains. On the fringe of the Andes are a string of important settlements
including Salta, Tucumán and Mendoza. Though the climate of this region is hot and dry, there
is sufficient water to support maize and pasture and a thriving wine industry, mostly relying
on irrigation. East of the Andes lie several ranges of hills, the most important of which are
the Sierras de Córdoba and the Sierras de San Luis. These are mostly of ancient Precambrian
rocks.
The Paraná Basin
The vast Paraná Basin stretches from the borders with Brazil and Paraguay to the Atlantic at
Buenos Aires. In the northeast it mainly consists of geologically recent deposits. The
easternmost part of this basin, between the Ríos Paraná and Uruguay, is the wettest part of
the country. Known as Mesopotamia and consisting of the provinces of Entre Ríos, Corrientes
and Misiones, it is structurally part of the Brazilian plateau of old crystalline rocks, the
'heart' of the South American Plate. Here there are undulating grassy hills and marshy or
forested lowlands, among them the Esteros del Iberá, an extensive area of flooded forest
similar to the Pantanal in Brazil. The horizontal strata of the rocks in this area is
dramatically evident in the river gorges to the north and the spectacular Iguazú falls shared
with Brazil.
The Chaco
Northwest of Mesopotamia and stretching from the Paraná and Paraguay rivers west to the Andean
foothills and north into Paraguay and Bolivia, lies the Gran Chaco, a vast plain which covers
the provinces of Formosa, Chaco and Santiago del Estero, as well as parts of Santa Fe and
Córdoba. It is crossed from west to east by three rivers, the Teuco-Bermejo, the Salado and
the Pilcomayo. Annual rainfall ranges from 400 mm in the western or Dry Chaco, a semi-desert
mainly used for cattle ranching, to 800-1200 mm in the eastern or Wet Chaco, where periodic
floods alternate with long periods of drought.
The Pampas
South of 33°S, the latitude of Mendoza and Rosario, is a great flat plain known as the Pampas.
Extending almost 1,000 km from north to south and a similar distance from east to west, the
Pampas cover some 650,000 sq km, including most of Buenos Aires Province, southern Córdoba,
Santa Fe and Entre Ríos, northeastern La Pampa and a small part of San Luís. This area is
crossed by meandering rivers and streams and there are many lakes, lagoons and marshes.
Geologically the Pampas are similar to the Chaco, basic crystalline and granite rocks almost
completely overlain with recent deposits, often hundreds of metres thick. Prevailing winds
from the southeast and southwest help to create the fine loess type soils which make this one
of the richest farming areas in the world, ideal for grasslands and cattle ranching. Being
comparatively close to the ocean, extremes of temperature are rare, another favourable feature.
A distinction is often made between the 'wet' Pampa and the 'dry' Pampa. The former, inland from Rosario and Buenos Aires is the centre of wheat, maize and other cereal production and the latter, west of 64°W, is where cattle ranching predominates.
The Patagonian Steppe
Patagonia extends from the Río Colorado (39°S) south to the Magellan Straits and covers some
780,000 sq km. Most of this area consists of a series of tablelands and terraces which drop in
altitude from west to east. The basic rocks are ancient, some classified as Precambrian, but
the surface has been subjected to endless erosion. Rainfall is lighter and the winds stronger
than in the Pampas frequently stripping the surface of cover and filling the air with dust.
Only where rivers have scored deep valleys in the rock base can soil accumulate, allowing more
than extensive sheep farming.
From the Straits of Magellan north to Lago Argentino (46°S) and beyond, a geological depression separates the edge of the South American Plate from the Andes. Most of Patagonia was under ice during the Quaternary Ice Age and has been rising since the ice receded. This area was presumably the last to be uncovered. However, considerable volcanic activity associated with the uplift of the Andes has taken place along the depression which is transversely divided into basins by lava flows. Alluvial and glacial deposits have created relatively fertile soils in some areas, useful for sheep and producing attractive wooded landscapes in the lake regions in contrast to the general desolation of Patagonia.
The Andes
Geographically the Isla de los Estados forms the southernmost extent of the Andes, which then
swing north to become the border between Chile and Argentina just north of the Paine mountains.
The 350 km section north of Paine is one of the most dramatic stretches of the Andes. The
crest lies under the Southern Patagonian Ice cap, with glaciers reaching down to the valleys
on both the Argentine and Chilean sides. On the Argentine side this has created the
spectacular range of glaciers found in the Parque Nacional Los Glaciares, the most famous of
which, the Perito Moreno Glacier, is one of the highlights for many travellers to Argentina.
The northern end of this section is Cerro Fitz Roy, which, along with the Torres del Paine (in
Chile) at the southern end, is among the most spectacular hiking and climbing centres in South
America.
Further north between 46°S and 47°S there is another ice cap, the North Patagonian Ice cap, centred on Monte San Valentín on the Chilean side of the border. North of this lie 1,500 km of mountain ranges rarely exceeding 4,000 m; on the east side of these are a series of attractive lakes, formed by a mixture of glacial and volcanic activity. The high section of the Andes begins at 35°S and includes Aconcagua, 6,960 m, the highest peak outside the Himalayas. For a further 1,000 km northwards, the ranges continue to the border with Bolivia with many peaks over 6,000 m, the Argentine side becoming progressively drier and more inhospitable.
