Antarctica is the world’s primary source for icebergs, generating the largest and most numerous found anywhere on the planet. An iceberg is defined as a large piece of freshwater ice that has broken off from a glacier or an ice shelf and is floating freely in open water. To be formally classified as an iceberg, the ice must protrude at least 16 feet above the sea surface and cover an area exceeding 5,382 square feet.
The Origin of Antarctic Icebergs
The creation of Antarctic icebergs begins with the continent’s colossal ice sheet flowing outward toward the sea. When the continental ice sheet extends over the ocean, it forms a thick, floating extension known as an ice shelf. These shelves are substantial, ranging from 50 meters to over 600 meters thick at their attachment point to the land.
The seaward edge of the ice shelf is constantly pushed outward by the ice flowing from the continent. Eventually, large blocks break away from the front in a process called calving. Calving is a natural process of mass loss that allows the ice sheet to regulate its mass. The sheer size of ice shelves, such as the Ross or Filchner-Ronne, means the resulting calved pieces can be immense.
The thickness of the shelf dictates the size of the iceberg, with break-up often occurring along pre-existing rifts. The icebergs then drift into the Southern Ocean.
Types and Scale of Antarctic Icebergs
The most recognizable form of Antarctic iceberg is the tabular iceberg, a flat-topped, steep-sided ice island resembling a vast plateau. These forms calve from the smooth, thick ice shelves, resulting in a length-to-height ratio greater than five-to-one.
A single tabular iceberg can be enormous, sometimes covering an area comparable to a small country. For instance, Iceberg B-15, which calved from the Ross Ice Shelf in 2000, initially measured approximately 11,000 square kilometers. The largest iceberg ever reliably sighted was an Antarctic berg measuring 31,000 square kilometers, observed by the USS Glacier in 1956.
While tabular forms are prevalent, calving events also produce smaller, non-tabular shapes. These non-tabular icebergs are classified by their appearance, including domed, pinnacled, blocky, or sloping forms. Regardless of shape, around 90% of the ice mass remains submerged beneath the waterline.
Tracking and Naming Giant Icebergs
The largest Antarctic icebergs are tracked globally because they pose a hazard to shipping lanes and influence oceanographic processes. The primary entity responsible for this monitoring is the U.S. National Ice Center (USNIC), a multi-agency operation that utilizes satellite imagery and remote sensing data. Tracking criteria apply to icebergs exceeding 20 square nautical miles in area or 10 nautical miles on their longest axis.
The USNIC assigns an official alphanumeric designation to these giant icebergs based on the quadrant of the Antarctic continent where they originated. The continent is divided into four quadrants labeled A, B, C, and D, moving counter-clockwise from the prime meridian. The letter is followed by a sequential number indicating the order in which the iceberg was tracked in that quadrant. For example, an iceberg named B-15 was the fifteenth iceberg tracked from Quadrant B.
If a named iceberg subsequently breaks apart into pieces large enough to warrant continued tracking, the fragments receive sequential letter suffixes, such as B-15A, B-15B, and so on. This standardized naming system allows scientists and maritime authorities to consistently monitor the movement and eventual decay of these massive floating ice masses.