What Causes Brazil’s Bizarre "Meeting of the Waters"?

Terry Feuerborn

Though it looks like a huge sandbar or rampant pollution, the Meeting of the Waters in Brazil is composed of water from the Rio Negro and Rio Solimões rivers. They meet up to form the Lower Amazon River, but do not mix together initially. This amazing phenomenon stretches for 6 km (3.7 mi) and is caused by irreconcilable differences in the water properties between the two rivers.

The Rio Negro, as the name implies, is a river of water that looks nearly black. It is relatively clear of sediment but has obtained its tea-like color from large quantities of plant material steeping in the water as it comes down through the jungles of Colombia. The water has an average temperature of 28 degrees Celsius (82.4 degrees Fahrenheit) and flows slowly at about 2 kilometers per hour (1.24 mph). 

The Rio Solimões, on the other hand, is a creamy cafe-au-lait color due to the large amount of sediment picked up as the water flows down the Andes Mountains. This water is quite a bit cooler at 22 degrees Celsius (71.6 degrees Fahrenheit) yet much faster than Rio Negro, as it flows about 6 kilometers per hour (3.7 mph). 

The difference in composition, flow rate, temperature, and density prevent the two from mixing when they initially meet. The contrast in color is so stark, this section of water can even be seen from space. Eventually, the water encounters obstacles that form heavy eddies, which churn the two rivers together.

It’s no wonder that this spot is such a popular tourist destination for those visiting Manaus, Brazil. 

Check out what this confluence looks like from NASA’s Earth Observing-1 satellite:

Image credit: NASA Earth Observatory/J. Allen/R. Simmon

[Header image “Meeting of the Waters, Manaus, Brazil, 2002” by Terry Feuerborn via flickr used in accordance with CC BY-NC 2.0]

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