Earth & climate
Glaciers & ice
Huge streams of ice that move slowly, shape valleys and tell us about the ice ages.
Imagine so much snow falls that it does not all melt away in summer. Year after year some of it stays, the snow piles up and its own weight presses it into hard ice. After many hundreds of years a glacier has formed: a body of ice so heavy that it slowly flows downhill.
How a glacier forms
A glacier only grows where more snow falls in winter than can melt in summer. Such places lie high up in the mountains or far to the cold north and south. Under the pressure of all the snow the tiny snow crystals move ever closer together, the air between them is squeezed out, and loose snow becomes dense, blue glacier ice.
Ice that shapes the landscape
A glacier shapes the landscape with enormous force. As it flows downhill it grinds down rock and pushes boulders ahead of it. In this way it planes narrow mountain valleys into broad valleys with a U-shaped floor. When the glacier later melts, the rubble is left behind as a long ridge called a moraine. Many lakes in the Alps lie exactly where a glacier once scooped out the ground.
The sun warms the sea, water turns into invisible vapor.
Ice ages and today
At the peak of the last ice age, around 20000 years ago, the Earth was much colder, and thick sheets of ice covered large parts of northern Europe and North America. About 11700 years ago this ice age came to an end. Since then it has grown warmer, and most glaciers have shrunk. Today many glaciers are melting especially fast because the climate is warming. Scientists measure them every year to see how much ice is being lost.
Exercises
0 of 6 solvedTime to try it yourself. You can't break anything, every attempt counts.
How does glacier ice form?
What valley shape does a glacier carve out?
A glacier flows about 30 metres downhill per year. How many metres is that in 4 years?
Put the formation of glacier ice in the right order.
- 1Snow falls and stays through the summer.
- 2Year after year more and more snow piles up.
- 3Dense, blue glacier ice forms.
- 4The weight squeezes out the air and compacts the snow.
The glacier tongue retreats by 15 metres each year. By how many metres is it shorter after 6 years?
Match each glacier term to the right description.