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An Overview of Icebergs

The Formation, Movement, Tracking, and Termination of Icebergs

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Icebergs

Icebergs in Disko Bay, Qeqertaq, Greenland.

Peter Adams/Getty Images

An iceberg is a large block or mass of land ice that has broken off from a glacier or ice shelf. This iceberg then floats in the world's northern and southern oceans and moves via wind and ocean currents.

Although icebergs have been in the world's oceans as long as there have been glaciers and ice shelves, their official study did not begin until the early 20th century because there was no official system in place to monitor them. In 1914, the International Ice Patrol (IIP), a branch of the United States Coast Guard, was formed to monitor icebergs in the Northern Atlantic Ocean in response to the sinking of the Titanic in 1912. The IIP, still active today, collects data on weather patterns, currents, iceflow, the sea's temperature, and salinity to monitor the movement of icebergs in that area.

Iceberg Formation

Most of the icebergs in the world's oceans today are descendants of the last glaciation when more than one-third of the Earth's surface was covered with ice sheets and glaciers during that time. Because of this immense amount of ice, the Earth's surface was highly reflective of the sun's energy which caused it to cool and allowed the ice to grow. As the Earth began to warm however, large pieces of the ice sheets and glaciers began to break off at the ice boundaries and collapse into the ocean. This process is called calving and it is responsible for the formation of all of the world's icebergs.

The majority of icebergs found today originally calved from ice sheets of Greenland and Antarctica and around 10,000 to 15,000 new icebergs clave each year. Smaller icebergs are found in places like coastal Alaska which calved from mountain glaciers making their way to the coast.

Although all icebergs form in roughly the same manner, those originating in the Arctic and Antarctic differ in form and size. Icebergs that have steep, narrow pinnacles (also called castle icebergs) form only in the Arctic regions while tabular or large, flat icebergs form only in the Antarctic regions. This difference is due to the type of ice as well as the structure of the land beneath. Pinnacle icebergs are steep because they typically calve off of mountain glaciers and tabular icebergs calve off of the flatter ice sheets in Antarctica.

Iceberg Shape and Size Classifications

In addition to the general pinnacle and tabular classifications of iceberg shape, there are several, more descriptive terms given to non-tabular icebergs (photos). The first of these is the dome, which describes an iceberg with a rounded top. A wedge iceberg is one that has one steep vertical side and a gradually sloping side, while a block has steep vertical sides and a flat top. Finally, a dry dock iceberg is one that is created by erosion and has a U shape or channel close to the water with pinnacles on either side.

In addition to their shape, icebergs are famous for their size and their ability to hide it under water. Typically, only one-tenth of an iceberg's volume is visible above the water's surface, while most of its mass is below and therefore unseen. This happens because the density if pure ice is much less than that of seawater.

In general, the total size of an iceberg ranges from 3-250 ft (1-75 m) and can weigh up to 100,000 to 200,000 tons. The largest iceberg in the North Atlantic was 550 ft (168 m) high. The largest in Antarctica, Iceberg B-15, which calved from the Ross Ice Shelf in 2000, was 183 miles (295 km) long and 23 miles (37 km) wide. It was estimated to have a mass of over 3 billion tones but has since broken up into smaller, though still very large, icebergs.

These are the sizes of the world's largest icebergs, but the IIP has created a classification system to categorize the size of all icebergs. The smallest is called a growler and is less than 3.3 ft (1 m) high and 16 ft (5 m) long. Medium icebergs range from 49-150 ft (15-45 m) high and 200-390 ft (60-120 m) wide, while very large icebergs are classified as anything over 250 ft (75 m) high and 660 ft (200 m) wide.

Iceberg Monitoring

In addition to the IIP, which monitors the Northern Atlantic's icebergs, icebergs worldwide are monitored by U.S. National Ice Center (NIC). NIC currently uses remote sensing to track ice in the polar regions and is the only organization to officially name and track icebergs in the Antarctic region.

To monitor Antarctica's icebergs, NIC assigns a letter value to each iceberg based on its point of origin. A begins in the Bellingshausen and Weddell Seas at longitude 0-90°W. The letters end at D in the Eastern Weddell Sea at the Amery Ice Shelf and a longitude of 0-90°E. Iceberg B-15 for example is called "B" because it originated in the eastern Ross Sea at a longitude of 90-180°W.

Iceberg Melting and Termination

Once monitored, the icebergs that flow into shipping lanes or the world's northern and southernmost harbors are typically broken up with icebreakers. These are ships with specially strengthened hulls and strong engines that allow them to push their bows into icebergs and use their weight to crack the ice. The broken ice is then pushed around or under the ship so it and other ships can safely pass through the area.

An iceberg's final termination then occurs upon reaching the warm waters of the Atlantic and Pacific. When icebergs melt in these waters, they often make popping and fizzing sounds. This is caused by the release of compressed air bubbles within the ice that formed when layers of snow compacted to form the ice. Therefore, because of their sensitivity to temperature icebergs are extremely limited in range.

To read more facts about icebergs, visit Canadian Geographic's "Just the Facts" page on icebergs.

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