An iceberg is a piece of glacial ice which has broken off and become free-floating. Although icebergs are found in the ocean, they are actually made from freshwater, and this contributes to their buoyancy in the ocean. Typically, around one tenth of an iceberg's mass can be seen above the surface of the water, with the bulk of the iceberg being submerged. This explains the common slang term “the tip of the iceberg,” used to describe a situation in which incomplete information about a situation is available.
When an iceberg breaks off in a process known as calving, it sets sail on a slow journey through the ocean. The iceberg will move with the ocean and wind currents, and its lifespan will be essentially indefinite, as long as it is not pushed into warmer regions. Many icebergs lose a bit of volume during the summer months, but as long as they are close to the poles, they can remain quite sizable. Over time, an iceberg may also break up into several smaller segments.
Scientists use a variety of terms to classify icebergs. Sizewise, they can be on the small end of the scale, as with bergy bits and growlers, or on the bigger side of the spectrum, with the imaginatively-named “large” icebergs. Icebergs can reach 75 feet (240 meters) in height. These massive chunks of ice can also be classified by shape, with terms like tabular, weathered, wedge, blocky, valley, pinnacled, dry-dock, domed, and arched being used to describe iceberg shapes.
People have been observing icebergs for centuries, and noting their role in navigation. In regions where icebergs are abundant, they can represent a serious threat to shipping, because they are difficult to see and challenging to avoid. Historically, numerous ships were lost due to iceberg collisions. In the modern era, ships avoid bergs by taking advantage of tracking data about especially large icebergs, along with utilizing technology which can be used to identify upcoming bergs in the path of a ship.
The number and size of icebergs in the world's oceans is closely monitored by researchers and scientists. An iceberg can present a navigation hazard, especially if it pops up in an unexpected place, but large numbers of big icebergs can also indicate that a glacier may be rapidly deteriorating. Several very large icebergs were calved in the early 21st century, including bergs the size of some American states, raising concerns about the health of the world's glaciers.