Tuesday, September 4, 2012

The Little Known Continent -- Amazonia

Most of the world has no idea what the Amazon is like. In fact, much of the interior of South America is unknown except to a few hardy explorers over the last couple of centuries, beginning with von Humboldt and Aime Bonpland, Von Spix and Von Marfitius, Bates and Wallace.

When we think of a continent, we think of ones like North America, Europe, Asia or Australia--even Africa. But South America is a unique continent, with the central part of Brazil and eastern Peru a huge cup-shaped basin about two-thirds the size of the entire United States (2.7 million square miles to 2.9 million square miles of the contiguous United States). 

Overlap showing the size of the contiguous United States overlaying the Amazon Drainage Basin

This area is typically referred to as the Amazon Basin, or Amazon Drainage Area. It covers 30% of South America, and is 2,720,000 square miles, and is the largest drainage area in the world, covering 25-degrees of latitude. Every year, the river rises 30 to 40 feet and floods 140,000 square miles--which is nearly twice the size of the state of Utah, which is the 13th largest state in the U.S.--and empties 11,000,000 cubic feet per second into the Atlantic--which is 20% of the world’s fresh water supply.

This drainage basin is unlike other continental areas even though it stretches over 4000 miles from the Andes to the Atlantic. Once off the mountain range, the final 4000 miles is about as flat as a pancake clear to the mouth of the Amazon River

Looking West at the Amazon Delta (middle right) and the flat Amazon Basin from the Atlantic Ocean. A flatter land covering about 2.5 million square miles cannot be found anywhere else on Earth

According to descriptions given from his 1870 exploration of the Amazon, Colonel George Earl Church describes the entire Basin as being barely above sea level with “the entire region simply an endless succession of channels, and small lakes, and swamps covered with  forest.” When the river level was low, the banks were 6 to 10 feet above the river level--however, the river would rise 30 to 40 feet in the wet season, flooding the banks and high ground, and the entire Basin. “In fact the water courses pursue a sinuous path and is everywhere interrupted by islands big and little, so much so that unless one refers to a chart it is difficult to know when one is really passing the mainland.” 

Church went on to describe the view as he sailed up the river. “Every now and then we passed a seringueiro's hut, or barracao, close to the water's edge, built on posts above the rise of the river, while  in front of it were tethered one or more canoes, the only means of transport, and indeed of refuge, when the water is very high. These huts were simple in construction, made of poles lashed together with bush  rope, the sloping roofs covered with broad palm leaves.”

The river flows uninterrupted for some 4000 miles, widening in places averaging about eight miles in width and finally to 158 miles in width at the delta. In many places the waterway is a lake-like expanse with islands in all directions. “It is difficult for one who has  not studied this subject particularly to appreciate how many thousands  of islands, big and little, are crowded into the lower Amazon.”

The lower Amazon is almost nothing but water for as far as one can see and beyond

As Church described his trip: “As the river was rising we passed through and by acres of floating  grasses, weeds, and logs, the larger masses being easily avoided. About 10 o'clock we entered the Narrows, our channel being perhaps 300  yards wide. On either side the low lying alluvial shores were thick. For miles we passed banks 10 or 12 feet above the water level and the impression was that the land sloped gently up from them. But when a break came in the forest wall, great meadows would be shown lower than the river bank. We also passed through the Narrows, that were uninteresting and dreary. My mental picture was of an expanse of water so broad that the shores dimly seen offered nothing of interest.”

He described that “From February until July, the ground is underwater and the seringaes are desereted by everyone, and that the river rises from 30 to 40 feet, forcing huge docks to be anchored a little way off shore, and when the river rises pay out the anchored cables so that the dock rises with it. Goods are sent ashore from these docks on long aerial cables, adding greatly to the cost of shipping.”

The channels in these lowlands are called igarapes (canoe-paths) by the natives--they can be narrow, but very deep. Everywhere one goes, the land is flooded every year and the tides sweep through the channels every day and overflow much of the ground so that it is always wet. Even the higher meadows are flooded in the wet season and canoes and even small steamers can pass over them.  The marshes among the meadows are called baizas to distinguish them from the forest swamps, or ygapos, showing the continual submergence of the land in the entire Basin."

The Amazon River meanders for thousands of miles through this lush forest where seeds float on the water until they can find lodging in the lowland swamps to finally sprout and grow

This entire Amazon Basin (about the size of the contiguous United States) even now is barely above sea level. At one time, just a few feet lower, and it would have been submerged, forming an entire ocean--a western extension of the Atlantic Ocean.

(See the next post, “The rising of South America,” regarding the rising of part of the South American continent)

No comments:

Post a Comment