Monthly Archives: July 2009

Orinoco Delta and Eastern Guyana Highlands

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Map of the Month: Orinoco Delta and Eastern Guyana Highlands

Map boundaries: 0 to 10 degrees North; 56 to 64 degrees West

Countries (States, Regions, or Districts): Brazil (Amazonas, Para, and Roraima), Guyana, Suriname (Coronie, Nickerie, and Sipaliwini), and Venezuela (Amazonas, Anzoategui, Bolivar, Delta Amacuro, and Monagas).

Overview

This map area extends from the Venezuelan coast range in the northwest to the Amazon rainforest in the south. Although the region is mostly tropical moist forest, there are areas of xeric vegetation in the northwest. Grasslands and savannas are found in the lower Orinoco and southwestern Suriname, and in La Gran Sabana where Brazil, Guyana, and Venezuela come together. In the Orinoco Delta and along the coast of Suriname are swamp forests that mark the transition from coastal mangroves to higher elevation tropical forests. The Guyana Highlands are notable for the tepuys, which are about 100 dramatic flat-topped sandstone mountains scattered across Venezuela, northern Brazil, central Guyana, and central Suriname. The most well-known tepuy is Auyan in southeastern Venezuela, from which Angel Falls plunges. Continue reading →

Madeira River Map of the Month

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Map boundaries: 0 to 10 degrees South; 56 to 64 degrees West

Country: Brazil (Amazonas, Mato Grosso, Para, Rondonia, Roraima)

Overview

This map area encompasses the drainage area of the largest, fourth largest, and fifth largest river systems in the world. The coverage is of the central Amazon basin (largest), lower Madeira drainage (fourth largest), and the lower Negro drainage (fifth largest). The Amazon River is as much as six miles wide as far as 1,000 miles upriver from its mouth. The Negro and Urubu, both north of the Amazon, are considered blackwater rivers, and the Tapajos (southeast area of the map) and Trombetas (northeast area of the map) are considered clear water rivers. The Madeira and Purus (central and southwest parts of the map) are considered whitewater rivers.

The map area is entirely covered by tropical moist forest, although forest formations vary in the northwest and southeast of the map. The campinarana of the northwest are heath forests believed to be short and shrubby due to low nutrient soils rather than seasonal dryness. The Mato Grosso forests of the southeast are tropical dry forests transitional between the Amazon rainforests and cerrado of central Brazil. Continue reading →