Iceberg is a huge mass of ice that has broken off from a glacier or ice shelf and is floating in water. Icebergs consist of snow compressed into ice. They can pose a danger to ships at sea. For this reason, the world’s major shipping nations track the locations of icebergs as they enter shipping lanes.
Icebergs come in many colors, shapes, and sizes. Most appear white, even though ice is clear. The white color comes from millions of tiny bubbles throughout the ice, which scatter the light passing through. Some icebergs include veins of bubble-free ice, which appear dark blue. There are even green icebergs. The green ice is frozen seawater containing green algae.
An iceberg is much larger below the water than above it. The mass of an iceberg above the water is about one-seventh to one-tenth of the iceberg’s total mass. The amount of mass above water depends on the amount of air trapped within the iceberg.
Antarctic icebergs.
The largest icebergs form at the edges of the Antarctic ice sheet. The world’s biggest icebergs are flat-topped icebergs called tabular icebergs. These icebergs calve (break off) from the Antarctic ice shelves. The largest look like floating tabletops many miles or kilometers across. These icebergs form when a long crevasse (large crack) gradually extends across the floating edge of an ice sheet. Over time, the crack extends all the way through the ice sheet, releasing the iceberg into the open sea.
In March 2000, one of the largest icebergs ever recorded separated from the Ross Ice Shelf. Named B-15, it was around 4,250 square miles (11,000 square kilometers) in surface area—about the size of the island of Jamaica—and possibly more than 1,000 feet (300 meters) thick. Even after drifting into the warmer waters of the Southern Ocean and breaking apart, some pieces survived more than 10 years.
Northern Hemisphere icebergs
are generally smaller than Antarctic icebergs. One of the largest Northern Hemisphere icebergs, called Ice Island T-3, was about 36 square miles (93 square kilometers) in area when it was discovered by the United States Air Force in 1950. Air Force Colonel Joseph Fletcher helped establish a scientific base on T-3 in 1952. Also known as Fletcher’s Ice Island, it supported dozens of scientists and was used at various times for more than 20 years. In 2010, an iceberg about 97 square miles (251 square kilometers) in area calved off the Petermann Glacier in northern Greenland.
Most icebergs in the Northern Hemisphere calve from tidewater glaciers, glaciers that end in water. These icebergs can plunge hundreds of feet or meters into the water or rise up from beneath the water surface to create spectacular waves and loud choruses of cracking and shattering ice. These icebergs are typically a few hundred feet or meters across. Hundreds form every day. Most are created by the many outlet glaciers flowing out of the Greenland ice sheet. These icebergs drift out into the waters surrounding Greenland. Many eventually drift into the North Atlantic Ocean, where they can threaten shipping between North America and Europe. One such iceberg was responsible for sinking the Titanic on April 14 and 15, 1912.
Icebergs and people.
International Ice Patrol is an organization formed in the aftermath of the wreck of the Titanic. The patrol monitors the North Atlantic shipping lanes for icebergs. Since 1914, the principal shipping nations of the world have financed the patrol. The U.S. Coast Guard does the actual patrolling. The patrol reports the position of icebergs and estimates their courses. Planes, ships, and satellites are used in patrolling.
Humans can do little to control icebergs. It is difficult to destroy an iceberg by blasting or to steer it out of a shipping lane. Sun, waves, and warm water eventually combine to break icebergs apart and melt them.
Ecology.
Icebergs play a role in polar ecosystems. As they melt, they provide fresh water to animals, such as plankton, living in the upper layers of the ocean. They also serve as breeding, hunting, and resting spots for birds. On the other hand, icebergs can interfere with feeding pathways used by seals and penguins.
See also Antarctica ; Arctic Ocean (Glacial ice) ; Titanic .
