Cathy Booth, age 10, of Calgary, Alberta, Canada, for her question:

Do glaciers really look blue?

Suppose we could make a perfectly clean glacier of plain, pure water. Its ice would be tinged very slightly with palest blue. On a clear day it would sparkle in the sunshine and borrow more blue from the sky. If it reached the shore, it would borrow even more blue from the sea. But real glaciers are made in the grubby world outdoors. Nature does not make them of the purest water and perfectly spotless ice.

Glaciers are made from crushed and crumpled layers of frozen snows. Even the whitest snowflakes gather dust as they drift down and blowing winds from afar add more dust to .the snows on the ground. The fallen snow also mixes with muddy clay and dirty pebbles. As it freezes, all this dirty debris is frozen into the hard, solid ice. Melting streams and oozing water dump more dirt into the cracks and crevices. Most glaciers are dirty white or grubby grey, more or less the same color as the wintry skies and seas around them. Even on clear days, their rough surfaces cannot reflect much sparkling blue from the sky and sea.