Icebergs, in the basic definition, are massive chunks of ice that have broken off from glaciers to float freely in the oceans. They can also break away from ice shelves. Icebergs can freeze together into ice packs. They can become ice islands in shallower water. And they can cause a condition called ice scour or ice gouging when they gouge the bottom of very shallow waters.
They are fresh water in composition. A large iceberg is estimated to weigh over 1 million tons or over 900,000 metric tons. Their shapes, sizes, colors and appearances are many.
Only one seventh to one tenth of the iceberg’s mass actually is visible above the line of the water. This is because the density of the freshwater ice is much less than the density of the saline sea water, so they float until the water becomes shallower.
Icebergs can be blown by winds or ride the ocean tides until they no longer float. Since ships tend to want to ride the tides and use the wind, icebergs are an incredible hazard to oceangoing vessels. They have the strength to rip through the thickest steel hulls both above and below the water line.
With some large icebergs standing up to 400 feet (or over 100 meters) in height above the ocean surface, the magnitude of the whole iceberg is astounding. The size and shape of the much larger submerged section is unknown, leading the the common expression “tip of the iceberg”, meaning that we only see so much and that much more is hidden.
The name “Iceberg” originates in the Dutch “ijsberg”, which translates to mean “ice mountain”. There are German, Low Saxon and Norwegian versions of the same word.
There is no universal official classifications for the sizes of icebergs. But the more common terms, from smallest to largest, are Growlers (named for their growling noises!), Bergy Bit, Small, Medium, Large and Very Large.
The largest icebergs can go for 200 miles, while Bergy Bits are about the size of a small house.
There are names for the differing shapes and figures of Icebergs. There are Tabular icebergs, with flat tops and steep sides. Domes are well rounded. Blocks look like blocks and have steep sides. A wedge is just a wedge, with a narrower top when seen from the side. A Drydock is in a U-shape, creating a form of harbor. Pinnacles are icebergs with a spire or with multiple spires.
When it comes to color and appearance, white icebergs generally have very tiny pockets of gases trapped in the ice structure. But there are icebergs that have collected various minerals, dirt, algae and rocks during their formation. There re blue, green, white, striped, purplish and other colors of iceberg, depending what was suspended or trapped when the ice froze.
Where are icebergs formed? According to NASA, North Atlantic Icebergs are formed from Greenland, which is almost covered in an ice sheet. North Atlantic icebergs disappear around the lower boundary of Newfoundland.
The Antarctic tends to host much larger icebergs that form from the Antarctic ice sheets. Comparatively, the largest North Atlantic iceberg was said to be 4 miles or 6.4 kilometers long. The largest Antarctic iceberg went to about 200 miles (320 km) long and 60 miles (97 km) wide.
Icebergs are a powerful and magnificent wonder of the world. Their size humbles us, and their variety of colors and shapes continue to fascinate us.
http://www.nasa.gov/worldbook/iceberg_worldbook.html
http://en.wikipedia.org/wiki/Iceberg
