We may think of icebergs as exiting and interesting things to see, but they are a great danger to ocean vessels when they drift into shipping routes. One of the greatest disasters at sea took place when the Titanic struck an iceberg on the night of April 14, 1912, and 1,513 people lost their lives.
An iceberg is a piece of glacier that has broken off. This happenes where the glacier( which are like rivers of ice) push down valleys until they reach the sea. The end of the glacier breaks off there and forms a floating iceberg.
Some glaciers do not reach the open sea but end in deep, steep-sided valleys called "fiords". The icebergs float down to the ocean from these fiords. In case of some galciers, the ends are worn or melted back by the waves. This leaves a big "foot" of ice submerged below the surface of the water. Such ice feet break off from time to time and rise suddenly to surface as icebergs.
Icebergs vary greatly in size. Small ones up to 5 or 10 metres across are often called "growlers" by seamen. But icebergs which measure over 100 metres are very common, and there have been some giant bergs seen that measured as much as 1000 metres across.
The ice in icebergs is only eight-ninths as heavy as sea water, so that only one-ninth of the iceberg sticks out above sea level and eight-ninths is below where it cant be seen. So a berg which rises 45 metres above the sea may extend 300 metres below! The amount of ice in an iceberg is almost unbelievable. Did you know that many of them weigh as much as 180,000,000 tonnes?
Because icebergs extend so far below the surface of the ocean, they dont drift with the winds but instead follow the ocean currents. Eventualy most icebergs are carried to lower warmer latituted where they melt. Very few of them last longer after they meet the warm Gulf Stream east of Newfoundland, Canada. But those that do become a menace to ships. That's why the United States Coast Guard maintains an iceberg patrol there to warn ships of the location of icebergs.