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From Andes to Amazon…. a title with perspectives.

The title roughly describes a cross sects through South America which can be linked with a bunch of disciplines of Earth Sciences. This is the reason that during our congress you will receive information of Earth-scientific research all dealing with this – from Andes to Amazon cross sect.
Consider the fact that this cross sect cuts our greatest drainage system of the world – the amazon river, which also harbors our greatest rainforest. Consider all their environmental consequences.
The cross sect also represents one of the most classical plate tectonic cross sects, which describes the active margin along the western border of S. America (the Andes) and after a few thousands of kms runs into the eastern Passive Margin, with its major Amazon delta system.
For that reason we can say … a title with perspectives.

river drainage system

First of all the cross secting visualizes the main headstream of the Amazon river system. The Amazon rushes through waterfalls and gorges high in the Andes mountains before entering the enormous tropical Amazon drainage basin.  Althought the river originates in the Andes Maountains only about 100 miles east of the Pacific Ocean, the reiver had decided flow across whole South America for nearly 4000 miles to reach the Atlantic Ocean on Brazil’s northeast coast. The largest portion of the basin are found in Brazil, but also includes parts of Peru, Bolivia, Exuador and Colombia. This drainage basin is the greatest system Covering a surface of 2.700.000 km2 which would The basin lies between the Guiana Massif to the north and the lower Brazilian Massif to the south cover whole Europe it is twice as large as any other river drainage basin in the world. The river is also the largest in terms of the quantity of and volume of water. With 6,275 kms of longitude it is the second longest river of the world, after the Nile.

The Amazon discharges between 34 and 121 million liters of water per second, and it deposits daily about three million tons of silts in the delta. The annual contribution of the river totals one fifth of all the fresh water that flows into all the oceans of the world, and it alters the salinity and the color of the Atlantic ocean up to a distance of about 186.4 miles (300 Kms.) from the delta.

So, why is Amazon so big? - The first reason has to do with it's location - right at the equator. Around the "belt line" of the earth lies a warm, tropical zone where over 400 inches of rain fall every year. That averages out to more than an inch of rain, everyday! A lot of water falls onto the land surrounding the river, what is called the "Amazon River drainage basin". Herein the second reason can be found. The Amazon drains the entire Northern half of the South American continent, including all the torrential tropical rains that deluge the rainforests, it carries an enormous amount of water.  A good way to understand what a drainage basin is to think of the whole northern half of the continent of South America as a shallow dish, or saucer. Whenever rain falls and lands anywhere in the river basin it all runs into the lowest place in the pan, which happens to be the Amazon River. The sheer volume of rain in the Amazon jungle, as well as the slope of the surrounding land, combine to create the enormous river known as the Amazon. The mouth of the Amazon River, where it meets the sea, is so wide and deep that ocean-going ships have navigated its waters and traveled far inland.

Amazon rainforest

The drainage basin harbors the largest rainforest in the world, the Amazon rainforest, lying in the tropical region of northern South America. The Amazon is thought to be second only to the human brain in complexity. The complexity is formed bys a massive and varied ecosystem, an integrate web of interaction between plants and animals that depend on each other for survival. The Rainforest covers over a billion acres, encompassing areas in Brazil, Venezuela, Columbia and the Eastern Andean region of Ecuador and Peru.

The Amazon is one of the largest remaining contiguous tracts of nature on earth. If Amazonia were a country, it would be the ninth largest in the world.

The Amazon Rainforest has been described as the "Lungs of our Planet" because it provides the essential environmental world service of continuously recycling carbon dioxide into oxygen.

Perhaps the most important function of all however, is that this vast wilderness has the power to regulate the global climate.

Twenty-five percent of the earths remaining primary forest is within the confines of the Amazon basin and a typical square mile may contain 750 species of trees, 125 different mammals, 400 types of birds, 100 distinct reptiles, and 16 varieties of amphibians.

The rivers support over 2000 species of know fish species, and new species found daily.

Insects make up the largest proportion of Amazonian organisms. Not only do they provide food for lower order insectivores, they serve vital functions in the whole scheme of Amazonian ecology.

Fascinating as all this is, what should truly amaze is the value the Amazon rainforest offers to man. It has given many of the foods we take for granted. Medicines that prevent the scourge of disease and death. And materials like rubber that are of sufficient commercial value.

 

Geology

The Amazon basin is one of the world’s largest subsidence troughs, spanning some 6 million km2. For nearly 500 million years, the Amazon basin has been accumulating immense quantities of sediment. Within the basin, two distinct groups of floodplain deposits are visible: the terra firme of Pliocene and Pleistocene age (10.000-5.300.000 years old), which lies above the modern floodplain; and the Holocene alluvial deposits (< 10.000 years old). The floodplain stretches from 12-30 miles in diameter on average, and is bounded to the north and south by low cliffs 20 to 60 feet in height.

Sedimentary system

Tectonics

The Amazon is essentially a giant river valley bordered to the north and south by the Guiana and Brazilian shields respectively, which comprise hard Precambrian rock. The total area of the Amazon Basin is 7.5 x 106 km (795 km2) of which about 80% is rain forest. During the Paleozoic the Basin was a huge marine inlet into which many tributaries flowed.

Until the Andes began to form at the end of the Miocene this inlet opened into the Pacific ocean and thus some elements of the Amazonian fauna are related to marine fish from the Pacific rather than Atlantic ocean. During the Quaternary water levels within the Amazon basin changed with the sea level. When the sea level was high, huge lakes formed in the valley into which large amounts of sediment formed.

During periods of low sea water level the rivers cut through the sediments forming river valleys. The modern sediments of the Amazon valley were formed during this period. These sedimentary deposits are up to 300 m thick and are called the Barreiras formation. Because these sediments have been heavily leached they hold low levels of nutrients and easily soluble cations such as calcium, and thus water flowing from the sedimentary deposits in the basin always has a low conductivity.
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