Gran Chaco
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What is the Gran Chaco?
The Gran Chaco is a lowland alluvial plain in interior south-central South America, meaning "Hunting Land" in Quechua. The Gran Chaco is largely uninhabited and is an arid subtropical region of low forests and savannas.
It is bordered by the Andes mountain ranges to the west and the Paraguay and Paraná rivers to the east. The northern boundary extends to the Izozog Swamps in eastern Bolivia, and the southern boundary reaches to about latitude 30° S, or roughly the Salado River in Argentina. It extends some 450 miles (725 km) from east to west and about 700 miles (1,100 km) from north to south, covering about 280,000 square miles (725,000 square kilometers). Slightly more than half lies within Argentina, a third in Paraguay, and the remainder in Bolivia.
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Where is the Gran Chaco located in South America?
The Gran Chaco is a lowland alluvial plain in interior south-central South America. It stretches about 450 miles (725 km) east to west and 700 miles (1,100 km) north to south, covering approximately 280,000 square miles (725,000 square kilometers).
The Gran Chaco is bounded by the Andes mountain ranges to the west and the Paraguay and Paraná rivers to the east. Its northern boundary reaches the Izozog Swamps in eastern Bolivia, and its southern boundary extends to about latitude 30° S, near the Salado River in Argentina.
More than half of the Gran Chaco is in Argentina, with a third in Paraguay, and the remainder in Bolivia. The portion of the Gran Chaco in Bolivia is commonly called the Bolivian Chaco.
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What kind of climate does the Gran Chaco have?
The Gran Chaco has climates that range from tropical in the north to warm-temperate in the south, but most of the region is subtropical. Average temperatures range from 60 to 85 °F (16 to 29 °C), with average relative humidity between 50 and 75 percent.
Great temperature contrasts exist, and the highest recorded temperatures for the continent occur in the Chaco. The highest average annual rainfall of 52 inches (1,320 millimeters) occurs in the east, decreasing to about 20 inches in the far west. Cool polar air from the south brings thunderstorms and strong, gusty winds that occasionally exceed 60 miles per hour.
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What types of plants and animals are found in the Gran Chaco?
The Gran Chaco plain is home to diverse plant and animal life adapted for its arid environment.
Plant Life
The eastern part of the Gran Chaco features a parklike landscape with clustered trees, shrubs, and tall savannas. Moving west, this transitions into a dry forest of spiny, thorny shrubs and low trees known as the espinal. The climax vegetation is quebrachales, consisting of low hardwood forests dominated by various quebracho tree species, which are economically important for tannin and lumber. In the more arid western Chaco, thorn forests and palm groves are common. A notorious plant is the vinal, considered a national plague in Argentina due to its hazardous thorns.
Animal Life
The Gran Chaco is abundant with wildlife, including jaguars, ocelots, pumas, tapirs, giant armadillos, spiny anteaters, foxes, wildcats, agoutis, capybaras, maned wolves, palustrian deer, peccaries, and guanacos. It is also one of the last major refuges for the rhea, a large, flightless South American bird. The streams host over 400 fish species, including the dorado and piranha. Reptiles are abundant, with numerous lizards and at least 60 snake species, including pit vipers and constrictors. Additionally, at least six species of poisonous tree toads have been identified.
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Who are the main indigenous peoples living in the Gran Chaco region?
The main indigenous peoples living in the Gran Chaco region include the Guaycurú, Lengua, Wichí, Zamuco, and Tupí-Guaraní. The Wichí, who live mostly between the Bermejo and Pilcomayo rivers in northeastern Argentina and Bolivia, are the largest and most economically important group. These groups subsisted as hunters, gatherers, and fishermen, with tribal units organized in extended families. Some groups like the Abipón, Mocoví, and Caduveo (Mbayá), adopted horses after the Spanish conquest, which had far-reaching consequences in the area. Today, most tribes practice some form of shifting subsistence agriculture.
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What environmental challenges does the Gran Chaco face today?
The Gran Chaco faces environmental challenges such as evaporation losses, deforestation, and livestock hazards. High temperatures and evaporation reduce effective precipitation, creating an arid environment, except in permanent swamps and forests along the Paraguay River.
The slow growth of quebracho trees, exploited for tannin, poses a threat to the tannin industry because harvesting can easily outpace reforestation efforts. Additionally, the vinal plant, with its long thorns, has become a livestock hazard in agricultural lands.
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Gran Chaco, lowland alluvial plain in interior south-central South America. The name is of Quechua origin, meaning “Hunting Land.”
Largely uninhabited, the Gran Chaco is an arid subtropical region of low forests and savannas traversed by only two permanent rivers and practically unmarked by roads or rail lines. It is bounded on the west by the Andes mountain ranges and on the east by the Paraguay and Paraná rivers. The Chaco’s northern and southern boundaries are not as precise: it generally is said to reach northward to the Izozog Swamps in eastern Bolivia and southward to about latitude 30° S, or roughly the Salado River in Argentina. Thus defined, the Gran Chaco extends some 450 miles (725 km) from east to west and about 700 miles (1,100 km) from north to south and covers about 280,000 square miles (725,000 square kilometres); of this total, slightly more than half lies within Argentina, a third in Paraguay, and the remainder in Bolivia.
The two permanent rivers of the Gran Chaco, the Pilcomayo and the Bermejo (Teuco), flow southeastward across the plain from their Andean headwaters to the Paraguay River and demarcate the three main regional divisions of the Chaco in Paraguay and Argentina: the Chaco Boreal north of the Pilcomayo, the Chaco Central between the two rivers, and the Chaco Austral south of the Bermejo; the portion of the Chaco in Bolivia commonly is called the Bolivian Chaco.
Physical features
Physiography
The Gran Chaco is a vast geosynclinal basin formed by subsidence (or downwarping) of the area between the Andean cordilleras on the west and the Brazilian Highlands on the east as it filled with alluvial debris from these two features. Because of its alluvial character, the Gran Chaco is nearly stone-free and is composed of unconsolidated sandy and silty sediments that are up to 10,000 feet (3,050 metres) deep in some places. The only rock outcrops of consequence are a few isolated remnants in Paraguay along the Paraguay River and some sandstone mesas in northern Paraguay and southern Bolivia.
Drainage
All but the extreme northwestern sector of the Gran Chaco is drained by west-bank tributaries of the Paraguay and Paraná rivers. The Bermejo and the Pilcomayo, even though they manage to traverse the Chaco, remain typical of most Chaco streams. Their courses are marked by countless sloughs, oxbow lakes, braided channels, sandbars, and vast swamplands; and they sustain such high losses from flooding, seepage, and evaporation that only a meagre portion of their full flow ever reaches the parent stream. Much of the Chaco is so poorly drained that the shallow, irregular channels on the exceptionally level plain lead to rapid and extensive flooding during the rainy southern summers (October to March). At the peak of these floods, as much as 42,000 square miles, or about one-seventh, of the area of the Chaco may be inundated, although some of this is caused as much by improper drainage of the impermeable subsoils as by overflow of the streams. Saline water is common in both deep and shallow wells, and the location and maintenance of freshwater supplies generally is a matter of chance. The problem appears to be greatest in the Chaco Boreal, although it has been suggested that the situation is more like that of the remainder of the Chaco or like the Argentine Pampa, where groundwater problems are not now considered to be as severe as early settlers and explorers had postulated.
Soils
Chaco soils range from sandy to heavy clay. Soils in the more humid east have more organic material and lateritic subsoils, whereas in the west the soils contain less surface organic material and have predominately calcareous subsoils. The local determining factor is drainage, whether a function of soil texture or of relative relief. Sometimes differences in elevation of less than three feet result in different soil types. Grasslands, or savannas, generally tend to be associated with sandier soils, bushlands with poorly drained clay soils, and the forestland with better-drained clay soils. In many cases, the high concentration of dissolved salts in the groundwater creates conditions in swampy sites that are intolerable to most plants, thus extending an arid appearance even into many areas where water is abundant.
Climate
With its considerable north-south extent, the Gran Chaco is subject to climates that vary from tropical in the north to warm-temperate in the south. Most of the region, however, is subtropical. Average temperatures vary from 60 to 85 °F (16 to 29 °C), with an average relative humidity between 50 and 75 percent. Great temperature contrasts exist, and the highest recorded temperatures for the continent occur in the Chaco. Average maximums are near 80 °F (27 °C), and absolute maximums may reach 116 °F (47 °C). The average minimum is about 57 °F (14 °C), although freezing winter temperatures can occur throughout the region.
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The highest average annual rainfall—52 inches (1,320 millimetres)—is in the east, and precipitation gradually decreases to about 20 inches in the far west. Although the rainfall normally would be adequate for agriculture, roughly a third to half of the total comes in the hot summer. Evaporation losses sharply reduce the effective precipitation and give the Chaco an arid nature that is absent only in the permanent swamps and forests along the Paraguay River.
Although light breezes are common, outbreaks of cool polar air from the south, called pamperos in Argentina, bring thunderstorms and strong gusty winds that occasionally exceed 60 miles per hour. These air masses move northward into the Amazon basin (where they are called friagems). The windiest season, however, is spring, during the transition from warm to hot weather. Dust storms may occur in the dry season.