South American River Basins

All three main South American river basins drain their three respective regions into the Atlantic Ocean. Those river systems that flow into the Pacific are very small and have little importance from a hydrological point of view. Although most of the fresh water they drain comes from rain water, about 15% of the water is from thawing snow piled up in the high-altitude gullies of the Andes Mountain Range. The major river basins of South America are:

1) The Amazon River Basin. It is the largest river system in the world, followed by the Mississippi, Volga, and Nile basins. The Amazon river rises in the Peruvian Andes under the name of Marañon River. As soon as it flows into Brazil, it changes its name and it is called Amazon, whose main tributaries are the Ucayali, Putumayo, Jura, Japura, and Madeira River. Half of Brazil, 60% of Peru, and 40% of Bolivia are drained by this river system.

2) The Rio de la Plata River Basin. It is the second largest fluvial system in South America. It drains a vast region, which includes Paraguay, Southern Brazil, Uruguay, and Argentina. The main water course is the Parana River, which receives waters from the Paraguay and Salado River. When the Parana joins the Uruguay River, they form the Rio de la Plata.

3) The Orinoco River Basin. Its main water course is the Orinoco River. Some of its left hand tributaries originate from streams in the Venezuelan Andes Range. The Orinoco and its tributaries drain most of the Venezuelan territory, including the large grassy plain, called Llanos del Orinoco.

Below, a map of South America showing you the three major basins of South America.


 

Zagros Mountains

The Zagros mountains form a long chain of snow-capped ridges and peaks in Iran, with Mt. Dena being the highest point at 4,409 m (14,465 ft.). This mountain range stretches along the western portion of Iran, in a northwest-southeastern direction, for about 1,600 km (990 miles). They run from southern Turkey and northeast Iraq to the southern parts of Persia. Green fertile valleys and plateaus are found in between these high ridges where people practice animal husbandry (livestock raising) and agriculture as their main sources of livelyhood.

The origin of the Zagros mountains dates back to the Jurassic period of the Mesozoic era, about 155 million years ago. They were formed by the orogenic collision of the Arabian plate under the Eurasian plate. The geological structure of this mountain range consists mainly of limestone, which is a carbonate sedimentary rock formed by compressed and mineralized organic materials. However, outcrops of Paleozoic era older rocks and boulders are found in the highest portion of these elevations. Several rivers, such as the Karun, rising above 4,000 of altitude, flow down into the Persian Gulf.

Below, map of the Middle East, showing Iran, Iraq, and the Persian Gulf. You can see the Zagros Mountain Range marked with brown dashes.


A high snow-capped peak in the Zagros mountain range in Iran.


 

Types of Basins in Geography

There are two types of basin in geography; an exorheic and an endorheic basin. In an exorheic basin, the main river flows out into the ocean, or sea; the Mississippi and the Loire river constitute exorheic basins, because they both runs into the ocean, draining a large tract of land. The largest exorheic basin in the world is the Amazon Basin in South America; it drains the third part of the South American territory into the Atlantic.


In an endorheic basin, on the other hand, the main river flows into a large isolated depression hinterland a continent, most of the time forming a fresh water lake, like lake Tanganyika, which is fed by Ruzizi, Malagarasi and Kalambo River, in Africa.

Concept of Basin

A basin is a large tract of land, or region, whose excess water, in the form of melting snow or rain water, is drained by a main river and its tributaries (branches). Converging brooks (creeks) form a secondary river, which is in turn a tributary branch as it flows into a main river, feeding more water to it. Therefore, as a geographical feature, it is a depression of the Earth surface the snow or rain water flows through, emptying an entire region.

Below, a map of the River Plate Basin in South America. We can see the tributaries (Paraguay, Parana, and Uruguay River) flowing into the River Plate, on whose shore the city of Buenos Aires lies.


 

European Cenozoic Rift System

The European cenozoic rift system is a series of elongated geological depression in the earth. Located in western Europe, it extends from the western Mediterranean to the North Sea for about 1,500 km, in an almost south-north direction. To the south, under the waters of the Mediterranean Sea, the Gulf of Lyon and the Valencia trough is a continuation of the European cenozoic rift system. In its onshore part, from south to north, it includes the Rhone depression, the Limagne, Bresse, and Saone grabens (elongated troughs), the Upper Rhine graben and the Leine graben.

The European cenozoic rift system began to form during the middle Eocene about 40 million years ago in its central part (southern Upper Rhine graben). Let's remember that the Eocene is the second epoch of the Terciary period. Then this system quickly extended to the south and north. It was locally accompany by strong volcanic activities. Thus, it evolved in the Alpine foreland, with the late phases of the Alpine orogeny.

Below, a map showing part of the European cenozoic rift system. The main grabens are in dark grey. The volcanic areas are marked in black. The numbers tell you the Moho depth in km.


 

Geological Folds

Geological folds are bends in a layer of rocks. It is a tectonic structure caused by deformation where several layers of rocks have been warped into wavelike, angular, and cylindrical patterns. They affect the horizontal layers of geological material as they are the result of the distortion of the Earth’s crust by powerful forces. Folds range in scale from microscopic in some fine-grained metamorphic rock to hundreds of kilometers across in old epeirogenic warps, with the Michigan basin being an example of it.

Overall, there are two kinds of this structural deformation: parallel fold, which keeps approximately constant layer thickness around the fold measured perpendicular to bedding; non-parallel fold, which has a variable layer thickness measured also perpendicular to bedding. Parallel folds are very common in Triassic limestone and shales of the Mesozoic era.

Parallel folds can further be divided into: 1) cylindrical parallel fold, whose layers of rocks completely curve around into a circular or cylinder-like pattern; 2) curved parallel fold, with the rock layers that compose it being disposed in the form of a curve, like segments of circular arcs; 3) angular parallel fold, whose layers of rocks are arranged at angles as they are more common and widespread than curved parallel folds. Most of the angular parallel folds date back to the carboniferous period of the Paleozoic era.

Curved parallel fold can even be further divided into synclines and anticlines. A Syncline is a downfold; in other words, it is a downward fold in which the strata of rocks convex downwards, in a trough-like pattern. An anticline, on the other hand, is a curved parallel fold that looks like an arch, with the curve being upwards.


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