June 20, 2003
The above picture was taken near the terminus of Mendenhall Glacier in early spring of 2002. In late spring and early summer, meltwater forms channels that produce these icy rivers. The blue coloring in the glacier ice is a result of light scattering and absorption in the densely packed ice crystals, which are approximately 4 times denser than the ice you would find in your freezer. Most all of the air bubbles in the ice have been eliminated as a result of the substantial pressure of overlying ice layers. Just like water, ice absorbs a bit more of the longer wavelength red and orange light than it does the shorter wavelength green and blue light. If the ice is sufficiently thick, so that sunlight has been scattered multiple times by the myriad ice grains, then it may appear decidedly blue.