Brazo Casiquiare in the river system of the Amazon
The Río Casiquiare is the left source of the river Río Negro, which in turn is the largest left tributary of the Amazon. Its catchment area, which lies almost entirely in southern Venezuela, extends north as far as the river bed of the Orinoco, by the way about a fifth of its water as Brazo Casiquiare ( Casiquiare arm) branches off to the south and the river systems of the water- richest rivers in South America, the Orinoco and Amazon, connects. This is the largest Flussbifurkation the earth; their existence has been kept to about 1800 for impossible, and their emergence is today only partially comprehensible.
Course and tributaries
In the wide, aufsedimentierten valley of the Orinoco at Tamatama the sluggish here current is divided: on the one hand in an approximately 90 m wide arm, sometimes sharp of turns to the left, and on the other in the remaining main stream at the western foot of the hill country of Guyana flows north. The soon almost in the opposite direction through the dense tropical rain forest southwest spiraling Casiquiare arm reaches selectively rocky ground and win by several large, almost entirely left tributaries significantly in volume and flow rate. Part of it forms small rapids. The direction of the Casiquiare often changes; particularly at the mouth of the larger tributaries he swung briefly on the valley lines.
The largest tributary is the approximately 440 -kilometer Río Siapa, whose clear water the volume of the Rio Casiquiare more than doubled. Its hardly explored the headwaters drained a large plateau, from which it descends through a cataract route. He is known for his great wealth of fish species, but also of blackflies. The second largest tributary, the Río Pasimoni, the Serra -do- Imeri massif drained with the Pico da Neblina, the highest peak near the border of Brazil ( 2,994 m). In an alluvial plain at the western foot of the hills there is a further bifurcation, which drains part in the Río Pasimoni, either directly to the Río Negro. Another major tributary is the Rio Yatua.
After the Casiquiare has included the northwestern direction of the Río Pasimoni, he deepened a little in the surrounding gently undulating hill country and meets at San Carlos de Rio Negro to the Rio Guainía, which also marks the border to Colombia. The Casiquiare changing its course by a cloudy white water river to a black water river with increasingly acidic water. The equal Río Guainía other hand, is a typical black water river without Aufsedimentierung.
Exist over water supply, length, catchment area and altitude of the river because of its remote location hard to beat traffic backed up data, which are also partly contradictory, partly inconclusive.
The Casiquiare branches, depending on the estimate, at low water between one tenth and one-fifth and at high tide between a quarter and a third of the water supply of the upper Orinoco from. Information to the average water flow at the junction fluctuate between 200 and 350 m³ / s (lowest monthly average: 127 m³ / s, highest: 680 m³ / s). Until Solano, near the confluence with the Río Guainía, the average flow rate is increased to almost ten-fold since the turn of the Orinoco. It is either 2.101 m³ / s or specified with 2,387 m³ / s. The Casiquiare has thus at the beginning about the size of the Moselle and in the end the size of the Lower Rhine. The Río Guainía, the other source of the river Río Negro has, at the confluence of almost the same size as the Río Casiquiare. At their confluence both rivers have a width of about 500 meters.
The length information for Casiquiare range from 300 km to 410 km; Measurements of the satellite images (2010 ) gives 354 km. The catchment area ( for the non- originating from the Orinoco part of the effluent ) is usually given as 42.3 thousand km ².
The elevation data for the start and the end point of Casiquiare differ. For the branch is specified as height 112 or 123 meters, for the confluence mostly a height of 91 meters. An occasional postulated reversal of the direction of flow depending on the water level differs in the overall slope of principle, this is at best a small scale in the branch area imaginable.
Development of the river basin and the bifurcation
The Rio Casiquiare flows through a registered ebnetes to peneplain hills of migmatites and quartzites of the Paleozoic era, which is located in the west of at least 1.8 billion years old Guyana Shield. This depicts the northern part of the craton, which forms the oldest part of the South American continent. This shield bulges since the beginning of the Tertiary period compared to the lowlands of the Amazon and Orinoco, and is overlain by also very old and resistant sandstones whose insular remnants tower over the hills as striking mesas. The hill country drained mainly to the northwest until the Tertiary auffalteten the Andes and since then their alluvial fans east always grow taller against the Guiana Shield left. The water from both sides now collects in the Orinoco flowing north.
In the south, meanwhile, a grave -like depression the Amazon opened the way to the Atlantic and also the area of the Río Negro sink. At its northern edge, and thus also in the field of Casiquiare, were characterized by and deflected by the current flowing to the west or north flows south to the Rio Negro, which is especially the neighboring Río Guainía unusual mouth angles of the left (north) leads tributaries.
The upper Orinoco cuts barely into the underground one; its sediments are deposited and fill the valley floor on and on. The reduction to the Amazon way helped in addition, that part of the Orinoco River water could eventually spill over into neighboring valleys south and these now also fills with sediment. This most tributaries of the deposits in the upper part of the schwebstoffreichen Río Casiquiare be dammed seeartig front of their mouths, like this is also typical of the Amazon.
The Río Casiquiare itself has a further, temporary bifurcation, which can drain water at high water level in the Río Conorichite. This is the right of the Casiquiare the valley line of the Río Siapa continued, also dammed up by Aufsedimentierung back its tributaries and empties into the Río Guianía, the other source of the river Río Negro later.
The southern catchment area of the upper Orinoco is successively toward the Río Negro " dumped ". In what order flow diversion took place, which eventually led to the development of Casiquiare, is still the subject of research.
Origin of the name
The name of the Casiquiare goes on living on the upper Orinoco Ye'kuana back (also Makiritare, such as: boat people, called ). The first of the European culture, who came in contact with their culture, was the Jesuit missionary, Manuel Román, of the connecting waters discovered on a Bereisung of the Orinoco to the Amazon in 1744. For the naming walked in his notes from the name of the Kashishiwari Ye'kuana for a mythical Ur - flow in the easier pronounceable form Casiquiare.
First customer of the flux linkage appears to be Walter Raleigh was happened in 1535 Francisco de Orellana and in 1596. 1639 reported the Spanish explorer Cristóbal de Acuña Diatristán from her. Also the more than 100 years later travelogue by Father Roman, presented by La Condamine, contradicted the then current postulate that flows above its mouth had a pure tree structure only, and thus came to sometimes passionate rejection. The river branch last doubt was confirmed by a Spanish expedition to the Orinoco border demarcation in 1755. However, could be overcome only in 1801 by Alexander von Humboldt, who captured this division on his trip to South America and mapped in naturalistic context. More precise mapping of the waterways leading into the 1924-25 Alexander H. Rice ( Harvard University) for the first time through with the help of aerial photographs.
Unlike Alexander von Humboldt had suspected, the Casiquiare developed no significance as a shipping route between the river basins of the Amazon and Orinoco. Changing sandbars and rock bars make the ride difficult for larger vessels. Since the construction of two large dams on the Madeira River, the idea of an inland waterway from the Río de la Plata, on the Flussbifurkationen in the north and in the south of the Amazon to the Orinoco is indeed again become current, this, however, the Isthmus of Pimichín more appropriate is held low Talwasserscheide in the Talung of the former, the Río Guainía deflected upper reaches of the Orinoco tributary Atabapo. Today, the Casiquiare is amplified traveled touristy, where contact with the indigenous people of the Yanomami in the foreground.