Glaciers are also called slow-moving rivers of ice. Most common in the polar regions of

the Arctic and Antarctic, glaciers can be found in the mountains of every continent

except Australia. Glaciers form in places where snow accumulates over time. It takes

decades, or even centuries, for glaciers to form. As the snow deepens, the weight and

pressure of the snow on top compresses the lower layers into ice. The weight of the glacier

plus the force of gravity will gradually cause the glacier to move downhill. Most glaciers

move very slowly, only about 160 feet or 50 meters per year, but some move as fast as

100 feet or 30 meters per day.

Glaciers are powerful. They can carve huge chunks out of mountains as they move downhill.

Because of this, they are sometimes called 'nature's bulldozers.' Like bulldozers, they

shape the land as they pass over it, but they do this in several ways.

First, glaciers pick up any material lying on the ground beneath where snow accumulates.

Water beneath the glacier soaks into cracks in the rock below. As the water freezes, it

forces the cracks wider and breaks off pieces of rock. This is called freeze-thaw weathering.

As the glacier flows downhill, it takes these loose pieces with it. This is called erosion.

These rocks and stones scrape along the glacier bed like sandpaper, taking more rocks and

stones with them. The ground beneath it becomes smooth as the glacier moves over it - this

is called abrasion. The glacier transports the eroded material downhill with it. Sometimes

you can see dirt and rocks in a glacier, which will give it a dirty appearance.

Once the glacier flows far enough downhill that temperatures are warmer, it begins to

melt. Anything that can't melt, like rocks, stones, sand, and clay, is deposited or left

behind as glacial till. The ice turns into meltwater and flows farther downhill to join

a lake, stream, or ocean. If a glacier reaches a body of water, pieces of it may break off

and fall into the water, forming icebergs.

Glaciers are only found in very cold parts of the earth, but during the last ice age

they could be found in parts of the world that are much warmer now. Even though the

ice is melted now, the landforms created by the movement of ancient glaciers can still

be seen today. Glaciers can create lakes, valleys, and other landforms, and are the

largest sources of fresh water in the world. As they move, glaciers change the shape of

the earth, making them one of the most dynamic natural features on the planet.