photos: Hoh rainforest, 10-11 Sep 2005

[eub]

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That blue Hoh River water -- I don't remember scattering mechanisms. Wikipedia says that glacial rock flour is "grains of a size between 0.002 to 0.00625 mm", 2000 - 6250 nm. I thought you needed to be smaller than the wavelengths of the light if you wanted preferential scattering of high frequencies. Help me out here?

Comments

[bhudson.livejournal.com]

I always assumed it was the colour of the rock itself that you saw. Rivers with a lot of clay sediment are red, after all.

[mh75.livejournal.com]

I have been led to understand, during various trips to national parks in the northwest, that the particular icy-blue color of the rivers is due to the presence of tiny particles in glacial run-off. Maybe its bogus.
If i were really bright i would use my presence at a physics lab specializing in water and arctic research to figure out the answer. I will see.

[bhudson.livejournal.com]

The question in my mind is whether the colour is due to the size of the particles (as Eli was implying), or due to the colour of the particles.

I am thinking the latter, since limestone quarries and glacial runoff are bright blueish-white much as the source rock is whiteish, while muddy rivers like my hometown Petitcodiac are, well, mud-coloured. But I don't really know, so I look forward to your discoveries.

[eub.livejournal.com]

What I should have done was to hold up some of the water to the sun and see if it was yellow-orange in transmission (meaning scattering) or was bluish (meaning color by plain old absorption).

[randomdreams.livejournal.com]

That's a really interesting question. I'll give it a try, maybe this weekend. I'd heard and accepted uncritically the scattering explanation. We have limestone-loaded and granite-loaded and sandstone-loaded glacial water hereabouts; I'd be a little surprised if they're *all* orange-absorbing.

[randomdreams.livejournal.com]

And this says:

"As the glacial mass of ice and embedded rock moves along the ground, it grinds the surface below and the rocks within it, creating a fine dust called "glacial flour." This flour makes glacial rivers look opaque and milky. The opaque water varies in color from chocolate brown to turquoise green, depending on the type and amount of sediment it contains. Streams that do not drain from glaciers are called clearwater streams to differentiate from those of glacial origin. Glacial streams can also run clear if the glacier is not melting, such as those seen during winter."

[eub.livejournal.com]

The chocolate brown sounds like a hint that absorptive coloring happens, but it leaves open the possibility that the turquoise is scattering coloring, from a different size of flour, doesn't it.

[randomdreams.livejournal.com]

I would totally believe that limestone or marble glaciers are absorptively blue rather than raman-scattering blue.

[eub.livejournal.com]

I could be convinced. I don't think of limestone as blue-green, but I don't know it very well. No idea what the Olympics are made of, either.