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

[beaq.livejournal.com]

Rock flour! I look at it, it mens COLD! Yay! (Perhaps, not, but it has that association for me.)

Might water suspension affect scattering? I speak from ignorance. I will aim laser friend this way, who might also speak from ignorance.

Does everyone take a picture of that spruce? It should charge five bucks a pop.

[hattifattener]

Hm. Yeah, the light will have a different wavelength in water. *scribble scribble* unfortunately, the effect works in the wrong direction: frequency's the same, velocity's slower (N=1.34 or so), so wavelength's shorter (500nm -> 373nm). So the rock flour grains are too small by a factor of several. Some possibilities:

• There's still some preferential scattering, even though the grains are too large; it's just not as strongly preferential as it could be
• There are smaller particles than the flour also in suspension
• Lies, lies, this is all lies. The streams are blue because the mountains scrape off bits of the sky

[hattifattener]

(Er, for "too small by a factor of several" above read "too large…", of course.)

[georgejas.livejournal.com]

yup, everyone takes pictures of that spruce. it's got a sign, and a pullout, and an exhibit, and it says "BIG SPRUCE".

i think it was 270 feet tall, and about that old.

[beaq.livejournal.com]

270 feet old! Yay!

Yeah, we took pictures of that tree a coupl'a weekends back, which is why I asked. :-)

[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.