Rivers of ice
A glacier is a big body of ice that moves across land. The word comes from the Latin glacies, which means ice. The Chinese word for them means ?ice river?. They cover about 10 per cent of all the land in the world. But they have around 70 per cent of the world's fresh water. If they all melted, scientists say, the oceans would rise by 70 metres. In Hong Kong, everybody would have to move to The Peak.
Some glaciers are huge. The Bering Glacier in Alaska, United States, for example, is nearly 200 kilometres long. No matter what their size, though, most glaciers are getting smaller - receding. After creeping down cold mountain slopes, they are now creeping back up. Some have disappeared altogether.
Mountains and the sea
Not all glaciers come down off mountains. An ice-cap on top of a mountain is a kind of glacier. Sheets of ice that cover large sections of land, like in Greenland, are glaciers too. Icebergs form from glaciers. When a glacier reaches the sea, it is called a tidal glacier. Where it touches the sea, sections of ice ?calve? - break - off and float out to sea.
The top of a glacier is called its ?head?. Its bottom is called the ?foot?. The head of a glacier does not move. But the foot of a glacier is always on the move. Usually, they move quite slowly - an average of two to three metres a day. A speed of 20 to 30 metres a day is very fast. The record in modern times is held by the Kutiah Glacier in Pakistan. In 1953, it travelled 12 kilometres in three months - about 120 metres a day.
