Mighty Glaciers

Mighty Glaciers

Introduction The Earth's surface constantly changes. Wind, water, and heat wear down mountains and crack stone. But some of the most dramatic changes are caused by giant pieces of ice and rock called glaciers (GLAY-shers). Glaciers move slowly over the land. They carve out cliffs, valleys, and prairies as they go. When glaciers melt, they leave behind lakes, rivers, and hills of soil and boulders.

Types of Glaciers Two common types of glaciers are continental glaciers and valley glaciers. Continental glaciers form at the north and south poles of the Earth. These huge sheets of ice cover vast stretches of land. Continental glaciers can be so thick that only the tops of mountains stick out above them. Much of Greenland and Antarctica are buried beneath continental glaciers.

Valley glaciers form on high mountains that rise above the snow line. Above the snow line, snow covers the ground all year. Even in the tropics, valley glaciers can form on the tallest peaks. Like rivers of ice, valley glaciers move through long, narrow valleys.

How Do Glaciers Grow? In some places, the temperature stays below freezing for most of the year. Snow piles up much faster than it melts. Each new layer of snow presses down on the snow beneath it. The lower layers of snow become squashed, or compressed.

The compressed snowflakes become ice crystals called firn. The firn crystals squash together as more and more snow presses down on them. Eventually, the firn turns into a huge slab of ice known as a glacier.