Encontro das águas

So.
My plan was to write about things that are weird here. Because there are things that are weird.)
But then this happened:

(Ok, this is a weird thing here, but it's not one I was going to talk about.)

Wh... What am I even looking at? There's... water? Two colors of water. Why are there two colors of water? Why are they not mixing? That's how diffusion works, after all.

Ok, so I went to this place yesterday. There are two colors of water, and they're not mixing. It's out at the river. (Unsurprisingly.) More accurately, it's at a point where two rivers meet. Even more accurately, it's a ~6 km stretch of river downstream from where two rivers meet.

Let's go to the GoogleMaps.

Ok, so what you can see here is first of all Manaus, in the top-middle. Right next to Manaus to the south there's Rio Negro. Even more to the south, there's Rio Solimões (is what Brasilians call the Amazon from here upstream. GoogleMaps calls it the Amazon, though). Rio Negro comes from Venezuela and Columbia, and Rio Solimões from Peru.
And they join. Here. In Manaus. Or... right next to Manaus.
The two rivers are different colors. Rio Negro is dark, and Rio Solimões is brown. Or yellow. Or sand colored. I suppose depending on who you ask. That's from all the mud it carries with it. Because that's what huge, flowing bodies of water do. So they join here (where you can see the pin in the map, in case it wasn't obvious), but they don't mix. Not right away.

Here's why.
Because temperature (and thus also density), and flowspeed. Rio Negro is warmer and slower, Rio Solimões colder and faster. The difference in temperature is about 6°C. That's warm enough to easily feel the difference. Which I did, from the boat. We went back and forth over the line while we tried the water with a hand. It was amazing. Rio Negro is almost 30°C, Rio Solimões a couple of degrees over 20°C. Rio Negro flows at about 2 km/h (though in all honestly, I don't know how fast that is for a river), Rio Solimões is more than twice as fast. So it takes them a while before they mix.

Let's see what it looks like from higher above.

(This is obviously not a picture I took, since I was on a boat, it's some Wikimedia Commons image. There's also a really good picture in the English Wikipedia that's from the other direction.)

What. I mean, the line between the rivers actually just keeps on going. If you compare it to the map above, you'll notice this picture is big enough to show the river a few kilometers downstream from where the first point where the rivers meet.

This whole thing is seriously weird. Ok, one more, a close(r) up of the water.

Not only can you see the difference farther away, but the line is right there, at the surface of the river. Of course it's not quite as straight as the line seen from a helicopter (or what ever was used to take the previous picture), but the line is still clear super-clear where it is. And there can be small pockets of water a couple of meters across on the side of the other kind of water. Because the line really is that clear.
Even knowing how it works doesn't make it less amazing.

Also: this river is enormous. We are still way way upstream in the Amazon (or, if you ask Brasilians, we are exactly where the Amazon begins), and that thing is already like 60 (or 70? the guide did tell us) meters deep and a few kilometers wide. And I'm assuming this, as other rivers, gets bigger the farther downstream you go, since more and more water gets dumped in from side-streams. The other option is speeding up, I guess. So bigger or faster, or a bit of both.

Lastly, here's a monkey:

It has nothing to do with the river, except that on the same river-tour we also went to this place where the monkeys live (which I assume is actually all over the place, but they're hidden in the canopy), and can be coaxed out with some banana. Yes, I actually fed a monkey banana today. Emphasis on both I and banana. It had these little tiny hands that for some reason surprised me despite the fact that that's like the definition of a primate.

Ok.
I'll hear from you on Friday.

~matu