Argentina's geography: a country watered from the east and dried by the Andes

How the Andes decide where rain falls

Argentina is shaped like an inverted triangle, about 1,420 kilometres across at its widest and some 3,800 kilometres from the subtropical north to the subantarctic south, in Britannica's measurements. The Andes run about 3,700 kilometres of that length along the western edge and form most of the border with Chile, a frontier of 5,308 kilometres.

The mountains do more than mark a border. Air coming off the Pacific loses its moisture crossing them, and the result is a rain shadow that runs down the eastern side of the Andes from the north-west to the edge of Tierra del Fuego. Britannica describes an arid core inside it rimmed by semi-arid steppe; the steppe gets about twice the rain of the desert, and in both evaporation exceeds precipitation, so neither grows trees. Patagonia shows the contrast at its sharpest: the western islands near Torres del Paine on the Chilean side receive 4,000 to 7,000 millimetres a year, the eastern hills less than 800 and the Patagonian plains as little as 200.

Most of the country's rain therefore falls in the north-east: on the Humid Pampa, in Mesopotamia between the Paraná and the Uruguay, and in the eastern Chaco. The rest of the territory gets moderate to light rain, and the driest areas are the far north-west and southern Patagonia. Argentina lies almost entirely in the southern temperate zone. Tropical air reaches Formosa and Misiones in the far north only occasionally, and because the continent narrows so sharply towards its tip, the two oceans keep average monthly temperatures above freezing in winter even at latitude 55° south.

Why the Humid Pampa carries the country

Pampa is a Quechua word for a flat plain. In Argentina the Pampas spread west from the Río de la Plata to the Andean forelands and south to the Colorado River, and their surface is thick loess broken only by occasional alluvium and volcanic ash. The one real relief is in the south of Buenos Aires province, where the Sierra de la Ventana rises to 1,239 metres at Cerro Tres Picos.

Britannica draws the line between the Dry and the Humid Pampa roughly along longitude 64° west. East of it grass grows knee-high in the most humid areas on thick dark soils; west of it the grass toughens and gives way to monte, a drought-tolerant scrub. Rainfall across the wider Pampas ranges from about 1,400 millimetres in the north-east to 400 or less on the southern and western edges, and western rainfall is highly seasonal, around 120 millimetres a month in summer against 20 in winter.

Much of the original plain has gone. Planted crops and trees have replaced much of the native flora, cattle and horses have taken over the ground that is not under crops, and guanacos are no longer found there. In the northern Pampas the salt lake of Mar Chiquita is fed by three rivers and has no outlet at all; its name, little sea, refers to the salt in its water. Soils change with the rain, from the light saline ground of the high puna to the dark, humus-rich earth of the Pampas. Rheas survive, along with small deer, introduced hares and the viscacha, a burrowing rodent.

Buenos Aires sits on the northern edge of the Pampas. Its summer months, December to February, average 22 to 24 °C and its winter months, June to August, 8 to 13 °C. Cold fronts moving north from Patagonia, mostly in July, bring occasional frost and snow to the Pampas and Mesopotamia, and very occasionally a dusting of snow to the capital itself. Windstorms called pamperos bring thunder, lightning and hail.

What the Andean north-west looks like

North of the upper Colorado River the Andes are at their highest. Ranges run north to south at 4,900 to 6,700 metres and are broken by high plateaus, the punas, and basins between 3,000 and 4,080 metres. Aconcagua, at 6,962 metres by the country's record and 6,959 by Britannica's, stands in Mendoza province, with several other peaks above 6,400 metres, some of them volcanic.

The puna is a treeless high plateau that continues west into the Atacama Desert in Chile. It holds salt pans, very little water and vegetation of dwarf shrubs and bunchgrass nearly as brown as the ground; it is the range of the guanaco, the llama, the alpaca and the vicuña. The east-facing slopes below it catch rain from the east, and forests climb them in bands: mistol above 500 metres, subtropical rainforest of laurels and cedars around 1,200 metres, cloud forest higher still, and the small crooked queñoa trees up to the timberline at 3,500 metres.

To the south-east the ranges break into separate blocks with flat basins between them, the Pampean Sierras, which Britannica compares to the Basin and Range country of the western United States. They rise from 700 metres in the Sierra de Mogotes to 6,250 metres in the Sierra de Famatina.

Further south lies Cuyo, most of San Juan and the centre and north of Mendoza. It is arid, with few clouds, a snow line at about 5,000 metres and few native trees. What makes it habitable is meltwater: the Desaguadero and its tributaries, among them the San Juan, the Mendoza, the Tunuyán and the Diamante, water the sandy deserts of Mendoza province.

Where the rivers of the north run

Aside from the Paraná and its main tributaries, Argentina has few major rivers. The Paraguay, the Paraná and the Río de la Plata drain some 3.2 million square kilometres, covering northern Argentina, all of Paraguay, eastern Bolivia, most of Uruguay and a large part of Brazil. The Paraná forms where the Paraguay and the Alto Paraná meet. The Río de la Plata is the estuary where the Paraná and the Uruguay come together, named for silver in colonial times before explorers learned there was neither a single river nor silver upstream.

Just above its meeting with the Alto Paraná, the Iguazú drops over the edge of the Brazilian massif. The falls lie on the border with Brazil, which holds part of them, and Iguazú National Park was inscribed as a World Heritage site in 1984.

The Gran Chaco to the west is the opposite of the Pampas in most respects. It falls in flat steps from west to east, drains poorly, floods in summer and dries in winter under a hot subtropical climate. In flood season its largest rivers wander through a maze of shifting courses, and long summer floods leave temporary swamps behind. Of its many rivers only three, the Pilcomayo, the Bermejo and the Salado, reach the Paraguay and Paraná system without evaporating into salt pans along the way. Thorn forest of carob and quebracho covers the west, and the forests thicken and grow taller towards the east.

Mesopotamia lies east of the Chaco in a depression 100 to 300 kilometres wide and about 1,600 kilometres long, between the Paraná and the Uruguay. Most of it is plain, parkland of wax palms and grass in the flood zones, with gallery forest thickening in Misiones, where the land rises and the soils turn rust and deep red. Jaguars, tapirs, monkeys and toucans live there.

The big dams are on these rivers. Yacyretá, on the lower Paraná, came on line between 1994 and 1998 and gave the country a surplus of generating capacity, according to Britannica.

Why Patagonia is windy and dry

Patagonia runs some 1,900 kilometres south from the Colorado River to Tierra del Fuego. East of the Andes its surface falls to the Atlantic in a series of broad flat steps, the same tectonic forces that raised the mountains having cut terraces along the coast. The coastal cliffs are low in the north and rise above 45 metres in the south. Rivers flowing east from the Andes, some of glacial origin, have cut broad valleys and steep canyons, and they lose volume as they cross the dry plateau.

The westerly winds do the rest. Most of the arid region is swept by winds carrying sand and dust, which in Patagonia leave a haze that cuts visibility. Steppe covers northern Patagonia between the Colorado and Comodoro Rivadavia, shrubland replaces it without trees except along streams, and low scrub alternates with grass steppe from Comodoro Rivadavia south to the tip of the continent. In the north-east corner annual rain barely reaches 500 millimetres and drops quickly below 300.

Irrigation follows the rivers. The Colorado and the Negro flood after the Andean snowmelt, and the Negro River irrigation district grows apples and pears. The Santa Cruz leaves glacial Lake Argentino in the foothills and crosses to the Atlantic. The lakes, Argentino, Viedma, Nahuel Huapi and Fagnano among them, sit in basins along the mountain front, and all of the country's major lakes are in Patagonia.

The Andean edge is wet by comparison. Villa La Angostura, near the Chilean border, receives about 2,074 millimetres a year, and Laguna Frías 4,400. Forests of southern beech, araucaria and conifers spread across the border into Chile. The national park system began here, with Francisco Moreno's donation in 1903 of 73 square kilometres in the Lake District, which became Nahuel Huapi National Park under the law of 1934.

Which land lies at the country's extremes

The provinces fall into six broad regions, each with its own land and water.

The lowest point is Laguna del Carbón in Santa Cruz province, at 105 metres below sea level. The southernmost point is Cape San Pío in Tierra del Fuego, at the entrance to the Beagle Channel, and the northernmost the confluence of the Grande de San Juan and the Mojinete in Jujuy. Glacial ice once reached beyond the Andes only in the far south, where large moraines remain.

Five of the country's twelve World Heritage properties are natural sites, and between them they sample these regions: Los Glaciares (1981) on the southern ice fields, Iguazú (1984) in the north-east, Península Valdés (1999) on the Patagonian coast with its whales, elephant seals and sea lions, Ischigualasto and Talampaya (2000) in the arid west, and Los Alerces (2017) in the Patagonian Andes. The national parks service groups its protected areas into the Northwest, the Northeast, the Centre, Patagonia, Southern Patagonia and the Argentine Sea.

Forest covered about 10% of the land area in 2020, 28.6 million hectares, down from 35.2 million in 1990.

What Argentina claims beyond its mainland

Argentina claims the Falkland Islands, which it calls the Islas Malvinas, and South Georgia and the South Sandwich Islands, all administered by the United Kingdom, and a sector of Antarctica, which is subject to the Antarctic Treaty. The United Kingdom's territory in the South Atlantic gives Argentina a maritime border with it near the Falklands. This catalogue records the claims and takes no position on them; Argentina: politics sets out how the dispute stands.

At sea Argentina claims a territorial sea of 12 nautical miles and an exclusive economic zone of 1,159,063 square kilometres. The southern tip of the country sits on the sea routes between the South Atlantic and the South Pacific: the Strait of Magellan, the Beagle Channel and the Drake Passage.