PUBLISHED : Monday, 26 April, 2010, 12:00am
UPDATED : Monday, 26 April, 2010, 12:00am

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.

In retreat

Experts who support the idea that our climate is warming study glaciers. One scientist recently called them ?canaries in the coal mine?. In old times, miners took canaries into mines with them. The small, sensitive birds died if there were poisonous gases. This was a warning for miners to get out. Receding glaciers are a warning that our planet is getting hotter.

One of the places in the world where glaciers are retreating faster than anywhere else is over the border. In Yunnan province , temperatures have been rising twice as much as the average in the rest of the world. Right now, the whole region is suffering a terrible drought. The Mingyong Glacier has receded nearly three kilometers in the past two centuries. But it is speeding up. In the past
10 years, scientists say it has receded half a kilometre.

now do this

1 Glaciers cover ? of the land in the world.

a. 70 per cent

b. 10 per cent

c. 15 per cent

2 The top of a glacier is called its ?

a. ice-cap

b. summit

c. head

3 The record for the fastest moving glacier in modern times was in ?

a. Pakistan

b. Yunnan province

c. Alaska


April 19

1. b, 2. a, 3. a