|
Amazon River Drainage System
First of all the cross section
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. Although the river originates in the Andes
Mountains (only about 100 miles east of the Pacific Ocean)
the river actually flows 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, Ecuador
and Colombia. This drainage basin is the greatest system
covering a surface of 2.700.000 km2.
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.
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.
|
