Gran Chaco - Geography

Geography

The Gran Chaco is about 647,500 km2 (250,001 sq mi) in size, though estimates differ. It is located west of the Paraguay River and east of the Andes, mostly an alluvial sedimentary plain shared among Paraguay, Bolivia and Argentina. It stretches from about 17° to 33° South latitude and between 65° and 60° West longitude, though estimates differ in this case too.

Historically the Chaco has been divided in three main parts: the Chaco Austral or Southern Chaco, south of the Bermejo River and inside Argentinian territory, blending into the Pampa region in its southernmost end; the Chaco Central or Central Chaco between the Bermejo and the Pilcomayo River to the north, also now in Argentinian territory; and the Chaco Boreal or Northern Chaco, north of the Pilcomayo up to the Brazilian Pantanal, inside Paraguayan territory and sharing some area with Bolivia.

Nowadays locals sometimes divide it simply in regard to the political borders, giving rise to the terms Argentinian Chaco, Paraguayan Chaco and Bolivian Chaco. (Inside Paraguay, people sometimes use the expression Central Chaco to the area roughly in the middle of the Chaco Boreal, where Mennonite colonies are established.)

The Chaco Boreal may be divided furthermore in two: closer to the mountains in the west, the Alto Chaco, or Upper Chaco, sometimes known as Chaco Seco or Dry Chaco, is very dry and sparsely vegetated, continuing eastward where less arid conditions combined with favorable soil characteristics permit a seasonally dry higher growth thorn tree forest, and further east again where still higher rainfall combined with improperly drained lowland soils lead to a somewhat swampy plain called the Bajo Chaco or Lower Chaco, sometimes known as Chaco Húmedo or Humid Chaco, with a more open savanna vegetation consisting of palm trees, quebracho trees and tropical high grass areas with a wealth of insects. The landscape is mostly flat and slopes at a 0.004 degree gradient to the east. This area is also one of the distinct physiographic provinces of the Parana-Paraguay Plain division.

The areas more hospitable to development are along the Paraguay, Bermejo and Pilcomayo Rivers. It is a great source of timber and tannin, which is derived from the native quebracho tree. Special tannin factories have been constructed there. The wood of the palo santo from the Central Chaco is the source of oil of guaiac (a fragrance for soap). Paraguay also cultivated mate in the lower part of Chaco.

Large tracts of the central and northern Chaco have high soil fertility, sandy alluvial soils with elevated levels of phosphorus and a topography that is favorable for agricultural development, but in combination with aspects that are challenging for farming: a semi-arid to semi-humid climate (600–1300 mm annual rainfall) with a six-month dry season and sufficient fresh groundwater restricted to roughly one third of the region, two thirds being without groundwater or with groundwater of high salinity. Soils are generally erosion prone once the forest has been cleared. In the central and northern Paraguay Chaco occasional dust storms have caused major top soil loss.