In some places it is cold all year long. On the tops of mountains it can snow any time of the year. When the first snow falls there is a lot of air space between the flakes. As more and more snow falls, the snow begins to pack together and get much heavier. The heavy snow compacts and presses down on the ground. Then when other snowstorms come the snow packs down even more, and the flakes start to lose their shape. Then the air gets sucked out of the flakes and most of the flakes turn into ice. The snowflakes get rounder as they absorb water in between the left over air spaces. As the years go by the the ice fields grow deeper and stronger until they form a glacier.
Glaciers move in two ways. The first way is through the pull of gravity and meltwater. Gravity pulls the heavy weight of the glacier down a hill very slowly. If you were watching one, you probably wouldn't see it moving. Under the glacier, as it slowly moves, the rocks it is dragging underneath cause the ice to melt. The water under the glacier is called melt water. The meltwater makes it slippery and helps the glacier to move down hills.
There is also meltwater on top of the glaciers that gets into cracks. When it refreezes the ice cracks and moves, kind of like the way an ice cube might crack and melt in a glass of soda. The amount of melt water in the glacier depends on the weather. Different parts of the glacier move at different speeds.
Do you ever wonder if anything lives on or in a glacier? The top of a glacier is only rocks, ice, dirt, and snow, so who or what would want to live there? Well actually, there is life on a glacier. The reason why is because of the wind. When the wind blows over the ground it collects dust and other things like insects, pollen, minerals, and bacteria that are in the air. Then when the wind blows over the glacier it drops everything on it.
Snow fleas and ice worms live on a glacier. The wind brings them their food. Ice worms are related to the earth worm, but much smaller. They are at less than an inch long!! They move around by squeezing in between the ice crystals at the top of the glacier. They can go as deep as six feet. Ice worms lay their eggs and hatch in the ice. Sometimes you can find over 100 ice worms in one area while another area won't have any.
Not many people get lucky enough to see ice worms and some people think they don't exist. Ice worms only live if the temperature is below 40 degrees Fahrenheit. If the ice gets below 22 degrees Fahrenheit, the ice worms will freeze. Ice worms only live in a glacier if it is beside the ocean or has a lot of meltwater. Ice worms eat algae, that is near the top of the glacier. Snow algae is red instead of green like most algae.
Along with the ice worm, some land insects like spiders and flies might live on a glacier. They usually get eaten by animals that are bigger, like the birds. Animals other the than ice worm also use glaciers. Tidewater glaciers give a home or resting place to large animals. Seals climb up onto the icebergs to have their babies. The new born babies, or pups, and their mothers can rest on the icebergs safe from their predators. Eagles like to stand on icebergs to look for food.
Some glaciers can be very small, maybe a few hundred square feet. Glaciers can be very thick. A glacier could get as big as 60 school buses on top of each other. The edges of a glacier are thinner than the center.
Did you know that no one has ever counted all of the glaciers in Alaska? There are nearly 100,000 of them, but most of them don't have names. Most of the glaciers are in the southern part of Alaska. About anywhere in Alaska where you drive or go boating, you can see the remains of the ice age and movement of glaciers.
A crevasse is an open break or cut in the surface of the glacier. They are dangerous because you can't always see them. It looks like part of the surface, but it really is a deep hole. Snow bridges form on top of crevasses.
Glaciers form valleys that are rounder and smoother than those that are formed by rivers. You can see the difference in these pictures.