Explainer: Ice sheets and glaciers
Here’s how and where these ice blankets form
Ice covers nearly all of Antarctica’s 14 million square kilometers (5.4 million square miles) of land. In some places, that ice is nearly 4 kilometers (2.5 miles) thick. It formed as snow piled up over many thousands of years. Gradually, the snow compacted into ice. Scientists call this vast, frozen blanket an ice sheet. A second, smaller ice sheet covers much of Greenland.
An ice sheet may look stationary, but it is always moving.
The lower layers are under crushing weight — in some places more than 350 times the pressure of Earth’s atmosphere (or 5,000 pounds per square inch). This pressure squishes the hard ice like soft putty. The ice oozes, flowing from the interior of the continent out toward its edges. In some places, this flow is very slow — only a meter or so per year. But scientists have also found fast-flowing corridors where the ice moves hundreds of times that fast. These ice streams — better known as glaciers — can be 40 kilometers wide and hundreds of kilometers long.
Unlike ice sheets, glaciers are widespread on our planet. They are found in mountain ranges around the world, from the Andes in South America and the Himalayas in Asia to the Alps in Europe. Fed by snow that falls on the mountains, glaciers flow down U-shaped valleys. Some will go on to feed rivers that empty into lakes or the sea.