h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

"Lake Louise is blue. It's the sort of blue that makes you think that your eyes have gone funny."

It certainly is and that statement reminds me just how readily I assume I know and understand things about which in fact I know nothing. I recall clearly the first time I saw a stream tumbling down a hillside in the Rockies, seeing its greenish tinge and "knowing" it was due to the minerals ground out by the glacier from which the water came. This in spite of the fact that I'd never seen Rockies or glacial stream before in my life nor studied them particularly.

I carried this knowledge about for years until I read somewhere that the minerals aren't greenish in the way I'd thought (How could they be, seeing as how they come from many different kinds of rock?) but have been ground by the glacial action to a size and shape which causes them to interact with light as they are seen to.

And this interaction with light explains why the sediment on the lake bottom appears different different colours from different angles. At least, I think it might.

I think you're right. When you're at the edge of the lake it appears to be crystal clear. It's only when you walk up the surrounding hills and look at the water from a different angle does it's true blue really stand out.

I always thought it was because of copper. I think that may be true for some streams in the UK (unless my dad was making stuff up to look clever ) but glacier streams are different.

Mmm…

Yes, glacier streams are different in that the stuff they carry is at least in part glacial flour, the stuff which has been ground pretty fine by a glacier.
I recall a water-filled disused quarry from early childhood, the water in which was green. We kids surmised, in the absence of your dad, that was because it reached the centre of the Earth.


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