An iceberg is an enormous piece of ice floating in the sea. "Berg" is the German word for mountain. In the coldest parts of the earth, around the North and South Poles, land and sea are both covered by sheets of ice, over 300 metres deep at the centre.
Tongues of ice, called glaciers, stretch out into the open waters of the oceans. The sea water melts the bottom parts of these glaciers, then the top part slides into the water with a mighty roar. The great piece of ice sinks for a short time beneath the surface then it rises againg, and floats away as a new iceberg. Some iceberg are miles across to begin with, and travel for thousands of miles and several years before they finally melt. The part of an iceberg which can be seen above the water is only about one-ninth of the total size. The rest is hidden beneath the waves.
One of the world's worst disasters at sea was in 1912 when the liner "Titanic" collided with an iceberg on her maiden voyage.