Icebergs are huge masses of ice floating in the sea. Only about one-ninth of it is above the level of the water. The rest lies hidden under the water. Icebergs pose a great danger to ships as they drift into the busy north Atlantic shipping routes. Sometimes they have to be towed away by powerful tugs.
An iceberg is actually a piece of a glacier that has broken off. A glacier is a moving river of ice. Glaciers from when snow accumulates, it hardens due to the pressure on it, and forms ice. Finally the ice brims over and flows slowly like a river downhill. Glaciers move at varying speeds, usually between 1 centimeter and 1 meter a day.
The middle part of the glacier moves faster than the edges, which rub against the sides of the valley. The moving glaciers are being downhill it cuts away at the soil and carries away huge rocks and boulders, these are then deposited on the front edge of the glacier in heaps called moraines. Glaciers move slowly down the mountain slopes and finally reach the sea. There, large pieces break off and drift away as icebergs.
Evidence of past glaciers can be found over much a larger area. During the Ice age most of the North America and northern Europe lay under ice. An ice age takes place every few million years. The last one took place about 10,000 years ago. During an ice age, temperatures are very low ice sheets cover large areas. About 10% of the earths land surface is even now permanently covered with ice. A body of ice that covers a large land surface or continent is called an Ice Sheet.
Most of the island of Greenland is covered with an ice sheet, which in some places reaches a height 3000 meters. A vast ice sheet in some places about also covers Antarctica. Glaciers are seen in the Alps, Himalayas, and the high mountain ranges of Alaska, Canada, Greenland, New Zealand and Antarctica.
The largest icebergs break away from the edge of the Antarctica. These icebergs are more flat topped than the Greenland ice sheet. They are not as large as the Antarctica ones but they are often taller. Icebergs begin to melt as they move away from the Polar Regions and reduce in size. Icebergs from Greenland last around 2 years while the ones of the Arctic and the Antarctica last for about 10 years.
