Iceberg

What is an iceberg?

Iceberg

Iceberg

An iceberg is a large piece of ice that has broken away from a glacier. Most icebergs are found in the ocean, but all consist of frozen fresh water. Icebergs are usually white, blue or green and extend above and below the water surface. They may extend downward 1,000 feet (305 meters) and reach a height of more than 200 feet (61 meters). The degree of submergence depends on the density, rock content and shape of the iceberg.
Icebergs float because the density of ice is lower than the density of seawater. The ratio of these densities tells us that 7/8 of the iceberg’s mass must be below water. Usually, icebergs are 20 to 30% longer under water than above and not quite as deep as they are long at the waterline.

The term “iceberg” probably originates from the Dutch term “ijsberg”, which means ice hill. In German, the word “berg” means mountain.

How do icebergs form?

Glaciers form on land as a result of a net accumulation of snow over thousands of years. Successive layers compress earlier accumulations until glacial ice is formed. Glaciers “flow” or “creep” outward under their own weight like a viscous fluid. When the edge of a glacier advances into the ocean, the pieces of ice that break off are what we call icebergs. The majority of icebergs in the North Atlantic come from about 100 iceberg producing glaciers along the Greenland coast.

The largest Northern Hemisphere iceberg on record was encountered near Baffin Island in 1882. It was 13 km (7.9 miles) long, 6 km ( 3.7 miles) wide and had a freeboard (height above water) of about 20 m (66 feet). The mass of that iceberg was in excess of 9 billion tons – enough water for everyone in the world to drink a liter (1.05 quarts) a day for over 4 years. Despite this staggering statistic, icebergs from Antarctica may be many times larger than this. In 1987 an iceberg with an area of 6350 square kilometers broke from the Ross ice shelf. That berg had a mass of around 1.4 trillion tons and could have supplied the world with 240 tons of pure drinking water.

How cold are icebergs?

The interior temperature of icebergs off the coast of Newfoundland is in the range of -15° to -20° C (+5° to -4° F). Only at the surface does the temperature increase to 0° C (+32° F) — the melting point. Oddly, icebergs in warm water appear colder than those in cold water because the fast melting steepens the internal temperature gradient exposing the cold interior.

What shapes do icebergs come in?

A fantastic variety of shapes result from the deterioration process of icebergs. Despite the fact that no two icebergs are the same, there are certain categories of shapes that are used for iceberg observation.

Iceberg Shapes

Iceberg Shapes

How stable are icebergs?

Often, icebergs are very unstable. Their highly random shape and non-uniform melting and breakup lead to frequent shifts in orientation. Tabular bergs are generally the most stable, whereas domed and wedge shaped bergs may roll completely over in seconds without any apparent provocation.

Other cool icebergs facts!

Icebergs are not salty. Remember that icebergs are comprised of pure fresh water. There may be some dust embedded in the ice and salt water may be on the surface, but it does not penetrate the ice. Icebergs are quite safe to consume.

When an iceberg melts, it makes a fizzing sound. The sound comes from the popping of compressed air bubbles which are in the ice. The bubbles form when air is trapped in the snow layers which are compressed to form glacial ice. Note that the released air is as old as the ice – thousands of years!

Icebergs appear mostly white because of the air bubbles in the ice. The bubble surfaces reflect white light giving the iceberg an overall white appearance. Ice that is bubble-free has a blue tint which is due to the same light phenomenon that tints the sky.

In Newfoundland, iceberg ice is “Harvested” for bottled water and vodka production. More products should be expected as more people enter the iceberg ice business.

Most of the iceberg information presented here is courtesy of Dr Stephen Bruneau, Ph.D., P.Eng. from Memorial University of Newfoundland.

Iceberg responsible for sinking Titanic

Iceberg responsible for sinking Titanic

This may be the actual iceberg responsible for sinking Titanic. The photo was taken in the vicinity where Titanic reportedly struck the iceberg.

Compared to others, the iceberg that Titanic hit was fairly small. Titanic survivors estimate that its height was about 100 feet above the water. It is estimated that the iceberg extended 500 feet below the surface.


Comments

  1. Author

    Only the tip of the iceberg is visible because the density of ice is 0.92 g/cm^3 and the density of seawater is 1.03 g/cm^3. The portion of the iceberg that is under water must displace enough sea water to support its weight.

    Lets assume A as the percentage of the iceberg that is under water:

    A ( ice V g ) = water V g

    The mass(g) units cancel volume and leaving:

    A = ice/water = .92 / 1.03 = .89 or 89%.

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