The lakes around Whistler - what causes the different colours?

Whistler Valley from near the top of Whistler Mountain.  Photographed August, 2015.

Blue.  Green.  Aquamarine.  These are some of the lake colours you see when visiting Whistler.  But what makes these such different colours?  

Arguably, we all know water is blue, but it really isn't.  Pure water is clear, and pure water in a shallow lake will also appear clear, revealing the bottom.  As the water gets deeper, that transparency slowly disappears.  That's because water absorbs light, long wavelengths (warm colours) faster than shorter wavelengths (cool colours).  As the water gets deeper, the reds and lower frequencies are absorbed first, leaving the higher frequencies, like blue.  Thus, deep water appears blue.

Shallower bodies of water may reflect more of the warmer colours, making them appear greenish.  This tendency is increased with the presence of phytoplankton like diatoms and other pelagic photo- synthesizers.  But that doesn't really explain what is going on in Whistler,

Glaciers are enormous, moving bodies of ice that grind and erode rock.  Finely ground rock, sometimes called boulder flour or glacial rock flour, is so small that it remains suspended in a water body.  These particulates can be measured using single digits using micrometers - a millionth of a meter.  Think a single millimeter divided by 1000.  These particles reflect blue and green wavelengths of light while absorbing the warmer shades.  The higher the concentrations of rock flour, the deeper the colour of the water.  

In the map below, you can see the same photo above with lake names.  The tarn (a small mountain lake, often formed from glaciers gouging out a depression), has the highest concentration of rock flour and so has a stronger colour associated with it.  Green Lake, aptly named, has a lower concentration of these fine particulates, and so the colour is less dense.  Alta Lake is blue because it is fed from a region with less rock flour, Nita lake even more so.

Did you notice the puddle?  It too is coloured, but not very much, as it isn't very deep.  Isn't that interesting?

Lakes in the Whistler area.

Thanks for reading.

Eric Svendsen     www.ericspix.com

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