Wednesday, September 12, 2012

The Rising of South America Part VII—The Eastern Highlands

We have written here in these last posts a great deal about South America, east of the Andes, once being underwater; however, it should be noted, that in addition to all the basins involved, somewhere around 4.5 million square miles of them, there are also highland areas to the east of the Andes. The most noticeable highland areas are in Guiana and Brazil. 

In Guiana is Mount Roraima (Roraima Tepui or Cerro Roraima), which is the highest plateau in the Pakaraima Chain. It is the triple border point of Venezuela, Brazil and Guyana and lies on the Guiana Shield in the southeastern corner of Venezuela’s 18,650 square mile Canaima National Park forming the highest peak of Guyana’s Highland Range. The tabletop mountains of the park are considered some of the oldest geological formations on Earth.
Mount Roraima was first described by the English explorer, Sir Walter Raleigh in 1596, and lies on the Giana Shield forming the highest peak of Guyana's Highland Range
This Guiana Shield juts up out of the ground in several table-top mountains and forms a highland area in the northeast corner of South America. The triple border point of Venezuela, Brazil and Guyana has 1300-foot-tall cliffs on all three sides.
Mount Roriama juts straight up out of the dense forest below. This sandstone mesa is called a tepuis, and there are over one hundred of these high, remote plateaus, that thrust up like rocky islands above the dense jungle.
Mount Roraima is part of the Guiana Shield which extends over an area of 18,650 square miles, 9000 foot high mountain plateau. It is considered one of the oldest geological formatioins on Earth.
Santo Antonio Waterfall on the Jari River, in the Tumucumaque National Park, Brazil
Just south of the Guiana Highlands is the Santo Antonio Waterfall, on the Jari River, which runs down from the Guiana Highlands and divides the Para and Amapa states as it flows 350 miles through the rainforest before joining the Amazon River at Bôca do Jari, opposite Grande de Gurupá Island, an area 3800 square miles with an elevation of only 15 feet. The flooded forests of this várzea region exemplify the incredible adaptability of species where trees, grasses and shrubs are partially submerged under water for months at a time.
Flooded Forests of trees and animals well adapted to life in areas under water six months or more out of the year
Normally in a drainage basin system, which is a part of a larger area of land that holds a certain amount of water in it, you will find that water actually converges to one point that’s usually found at the very bottom. This point of convergence is where the water usually exits from the basin in order to connect or join with another body of water that’s larger, such as a lake, ocean, sea, river, or wetland. Drainage basins can be either closed or open. Closed basin systems have water that converges to a point found inside the basin itself, usually referred to as a sink, where the water usually disappears to underground—however, in the Amazon Basin, though the excess water does drain to the Atlantic, much of the 2.7 million square miles has standing water, called swamps, because there is nowhere for the water to go—there is not enough slope to the land and there are no sink holes since the land is saturated both above the below the surface.

The Amazon Drainage Basin flows eastward (red arrows), from a high of 400 feet above sea level to the east coast, dropping 400 feet in 4000 miles, emptying between the Guiana Highlands and the Brazilian Highlands, the latter marked by the Table Mountain in the Brazilian Shield. During the wet season,this area is flooded, with the river levels rising as much as 30 to 40 feet.
Chapada Diamantina National Park in northeast Brazil covering an area of 950 square miles. Though in the Highlands, the plains below are quite low and drop quickly to the level of the Amazon Basin
Chapada means “a place with steep cliffs” and there are many of these in Brazil, and are mountain ranges with vertical walls or just a singular rock formation that suddenly rises up from the surface. These mountains, part of the Brazilian Highlands,stand as sentinels over the lowlands below in the Amazon Basin.
The Beni savanna, also known as the Moxos plains, is an alluvial floodplain that forms a mosaic of forest islands scattered across a flooded savanna landscape. It is a tropical savanna region of northern Bolivia that covers an area of 48,700 square miles in the lowlands of northern Bolivia, with small portions in neighboring Brazil and Peru. The low level of the savannas, coupled with wet season rains and snowmelt off the Andes, cause up to half the land to flood each year. The savanna, a flat grassland with scattered trees, is surrounded by tropical moist forests—the Amazon moist forest to the north, west and south, and the Madeira-Tapajos moist forests to the east, converting vast parts of the region to swamp.   This Basin, from its low elevation of 1300 feet in the west at the base of the Andes, drops quickly to 295 feet before spreading across eastern Bolivia into Brazilian Basin. 
Beni Savanna begins in the western part of Bolivia and spreads northeastward into Brazil. It is flat and fairly level, dropping 295 feet over a 4000 miler distance
The area can only be accessed from its northern and southern sides. In the north the protected area is accessible through the Mamoré, Sécure, and Isiboro rivers. There are no passable roads, just a handful of dirt trails that can only be traveled during the dry period (May through September) and connect the various indigenous communities.
This overall area east of the Andes stretches to the east coast, skirting the few highlands in the east, such as the Guiana and Brazilian highlands, to reach the Atlantic. The run of level land, barely above sea level, is one third longer than the distance from San Francisco to New York, yet the land drops less than four hundred feet across the entire distance. It would not have taken very much to lift the entire lowlands of South America upward out of the water to sit barely four hundred feet above the sea.
(See the next and last post in this series, “The Rising of South America, Part VIII—Barely Above Sea Level,” to see how the people live within the Amazon Drainage Basin that is flooded for several months each year)

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