The view of Lake Louise from the Fairview Lookout:
Ever wondered why Lake Louise is so colourful?
We all know that clear water has a slight blue tint to it. This is because water absorbs the longer wavelengths of light (reds, oranges, yellows) but strongly reflects and transmits the shorter blue and blue-green wavelengths. This is best seen with a reflective surface beneath - imagine a swimming pool or a clear tropical ocean with a white sandy beach. Glacial-fed lakes get their bright colours from very small pieces of clay, silt and rock called rock flour. You can see what rock flour looks like in the image on the right. To begin with, the rock flour provides a surface upon which light can be reflected into our eyes. More importantly, the rock flour absorbs some blue light, but also reflects some blue, green, yellow, orange and red. So the rock flour absorbs some blue and the water absorbs the yellow, orange and red. What remains to be reflected back into our eyes? Some blue and mostly green! That's why Lake Louise is turquoise in colour!
Where does this Rock Flour come from?
Rock flour is made from the grinding of glaciers against the hard bedrock. You could almost think of the glacier as sandpaper that breaks apart the hard rock into tiny microscopic pieces. The rock flour is then collected by glacial runoff and is deposited into the lake. The rock flour is microscopically small and is deposited into Lake Louise due to the nearby glaciers, including the Victoria Glacier. It is thought that the glacially-fed lakes of the Canadian Rockies are so brilliant in colour because of the limestone bedrock. Limestone creates flat, flakey pieces of rock flour which are highly reflective.
Rock Flour being Deposited into Lake Louise:
Some Mathematics of Rock Flour
As mentioned earlier, rock flour is microscopic - typically somewhere between 2-4 micrometers in size. Particles this small don't simply sink within seconds in water like you might expect from a grain of sand. In fact, it takes much longer for the sedimentation (falling due to gravity) of rock flour! Following a few assumptions, here is a simplified formula to determine the sedimentation rate of rock flour:
Given that the density of rock flour (1089 kg/m3), the density of water (1000 kg/m3), the acceleration due to gravity (9.81 m/s2), and the viscosity of water (0.01 Pascal second) can all be generalized as constants, we can obtain an equation for the sedimentation rate of rock flour as a function of particle size:
To Log this Earthcache Answer the Following (email answers to cache owner):
1) What is the full GC code for this Earthcache?
2) How would you describe the colour of Lake Louise during your visit?
3) Is the water clear or does it appear milky? Briefly describe why.
4) In which season would the deposition of rock flour into Lake Louise be greatest? Briefly describe why.
5) Would the addition of extra rock flour into Lake Louise make it look bluer or greener?
6) What is the sedimentation velocity of a rock flour particle with a radius of 2 µm (in meters per year)?
7) The maximum depth of Lake Louise is 70 meters. Using your answer from above, how long would it take for the particle of rock flour to reach the bottom of Lake Louise? Assume the lake is still and doesn't freeze.
As always, you are encouraged to share your favourite photos of Lake Louise! The posted coordinates are an amazing place to take photos. If you are looking for a hike, the Fairview Lookout, Little Beehive, Big Beehive and Mount Fairview are all marked trails which offer spectacular views of Lake Louise.