A glacier is a large flowing ice mass. Some glaciers move at a snail's pace, just a few inches a day, while others advance more than a hundred feet a day.

Glaciers are formed as large amounts of snow accumulate over many years and individual snow flakes at the bottom of the snow pile are compacted into grain-like pellets called firn.

An iceberg floats in the ocean.

Glacier ice can move as much as 1 foot each day! 

Scientists are interested in glaciers because these chunks of ice can be used to study global warming. People are putting more carbon dioxide gas into the Earth’s atmosphere, or air, every year by doing things like burning coal for electricity. Like a blanket in the atmosphere, that carbon dioxide traps heat and warms the planet.