Glacial Lake Color
Lake Louise, Banff National Park, Canada is fed by melt water from the Victoria Glacier that is visible in the crotch of the vee in the center of the photo. Click on the image for a larger photo.
The physics demonstrated by this picture is the turquoise
blue of the lake water characteristic of all glacier-fed lakes
and rivers. Fine rock flour - caused by the relentless
grinding of the rocks in the glacier - is suspended in the
meltwater and is chiefly responsible for the spectacular
blue-green color. Detailed physical explanations are
rather lacking, however. Guidebooks state that the color
is the result of diffraction of light by the fine
particles. However, the size of the particles have been
measured, and the smallest particle sizes are about 5 microns
across - about 10 times the wavelength of visible light.
Therefore diffraction of light is not a principle
A simpler explanation than diffraction is reflection of
transmitted light by the suspended particles combined by the
reflectivity of the rock composition that makes up the
particles. Imagine a swimming pool (even an indoor pool)
containing clear water with white tiles lining the pool.
The water reflected from the white bottom appears blue due to
weak absorption of light by water in the red region of the
"Blue Ice" PPOW for March 12, 2010). The fine rock
dust suspended in glacier-fed lakes acts the same as the
bottom of a pool, except the reflective surfaces are at many
different depths in the water - not just on the bottom.
Deeper particles reflect light that is bluer than the shallow
particles, thus the cumulative effect of light reflected from
all depths is a combination of different ratios of all colors
relative to blue light. The composition of the rock
flour is another major contributor to the water color.
Physics Photo of the Week is published weekly during the academic year on Fridays by the Warren Wilson College Physics Department. These photos feature interesting phenomena in the world around us. Students, faculty, and others are invited to submit digital (or film) photographs for publication and explanation. Atmospheric phenomena are especially welcome. Please send any photos to firstname.lastname@example.org.
All photos and discussions are copyright by Donald Collins or by the person credited for the photo and/or discussion. These photos and discussions may be used for private individual use or educational use. Any commercial use without written permission of the photoprovider is forbidden.