THE AMAZON BASIN: Amazing Facts
The Amazon basin has the most developed rainforest of
anywhere in the world. Over two-thirds of all the fresh water on earth
is found within the Amazon basin and over 20% of the earth’s oxygen is
produced there. Although exact numbers are not known, the basin may
contain up to one million plant species. The Amazon basin is drained by
the Amazon River and its thousands of tributaries. The basin covers an
area of approximately 2.5 million square miles (650 million hectares) which is approximately
40% of South America. If superimposed on the United States, it would
cover nearly all of the contiguous 48 states!
The headwaters of the Amazon River are in the Andes
Mountains of Peru and a mere 120 miles (190 km) from the Pacific Ocean. From
there the River stretches eastward for approximately 4,000 miles (6,400
if finally empties into the Atlantic Ocean at Belém in Brazil. Over
this 4,000-mile length no bridge crosses the Amazon. There are
approximately 1,100 tributaries that service the main river, seventeen
of which are over 1,000 miles (1600 kilometers) long; the Río Negro is the most dominant
The tributaries vary in color from cloudy yellow, to
clear black depending on the soil and vegetative environment of the area
they are flowing from. Seasonal flooding brings soil and minerals from
the mountains to the flood plains along the river, enriching the
nutrient poor soil. The water level in the Amazon River can fluctuate by
as much as 40 feet (12 m). The lowest levels occur in the months of August to
September, and the highest levels occur in April and May. When the water
is at its high point the River can be as wide as 300 miles (560 km), and at this
time up to 500 billion cubic feet (14 billion m3) of water surge out to sea per day.
Imagine… this is enough to sustain New York City’s fresh water
supply for nine years!
The River’s deepest point occurs near the Atlantic
Ocean where its depth is about 121 feet (37 m). The flow of the effluent into
the Atlantic is so strong, that the waters of the Amazon River do not
even begin to mix with the ocean water until the water has flowed 125
miles (230 km) into the Atlantic. This incredible force is generated purely by
the sheer volume of water that flows, not by a seep gradient; indeed,
the gradient from 2300 miles (3700 km) inland to where the Amazon meets the ocean
would be barely enough to drain a bathtub!
Interestingly, millions of years ago the Amazon used
to flow westward toward the Pacific Ocean. This was when South America,
Antarctica, Africa, Australia and India were one big continent known as
Gondwanaland. As the continental plates shifted, South America broke
away, moved westward and collided with the Pacific Ocean plate. This
collision gave rise to the Andes Mountains; subsequently the flow of the
Amazon water was blocked and a vast inland lake was formed. Later
geological forces caused a breach in the east, and in what must have
been a cataclysmic event, the vast lake rushed into the Atlantic Ocean
and as it did, created the river we now call the Amazon.
The Amazon is teeming with life. It is a birders
paradise containing more species than any other ecosystem, and there are
more than 4,000 species of butterflies. The lush forests of the Amazon
basin are home to reptiles, amphibians, primates, tapirs, capybaras,
even jaguars. The river itself contains freshwater dolphins, manatee and
more than 2,000 species of fish which incidentally is more species than
has been recorded for the entire Atlantic Ocean!
The climate in the Amazon is consistent with daytime
temperatures ranging from the mid to upper 80’s and falling to the low
70’s in the night. Rain falls approximately 250 days of the year.
While many areas have distinct rainy and dry seasons, others do not.
Even the high water level is not necessarily dependent on rainfall
during the rainy season, but on other factors such as the rate of
evaporation and transpiration of plants. There are about 100 inches (250
rainfall per year in the Amazon with the forest creating about half of
its own rainfall. This intricate water cycle has helped to create the
diversity of life found in the Amazon basin and has sustained its
existence for millions of years. It remains to be seen what devastating
impact the human intervention of deforestation will have on this cycle.