An iceberg is a sizable mass of freshwater ice that has detached from a glacier or ice shelf and floats in the ocean. They are common in the seas surrounding Antarctica, the Arctic and subarctic regions, Arctic fjords, and glacier-fed lakes. Antarctic icebergs often calve from floating ice shelves, forming large, flat tabular structures that can range from kilometers to tens of kilometers in diameter, with a thickness of 200–400 meters and a freeboard of 30–50 meters. These icebergs typically weigh several billion tons. Arctic icebergs mainly originate from fast-flowing glaciers from the Greenland Ice Sheet and are generally smaller and more randomly shaped than their Antarctic counterparts.

How do icebergs form?

Icebergs primarily form through calving, where large chunks of ice break off from glaciers or ice shelves. In Antarctica, icebergs often originate from floating ice shelves, which are extensions of continental ice sheets. Pressure from the flowing ice causes these shelves to move seaward, eventually fracturing due to stresses from currents, tides, and wave action. Arctic icebergs mainly come from fast-flowing glaciers from the Greenland Ice Sheet. The glaciers experience stresses that lead to the formation of crevasses, which become part of the iceberg structure. Several factors can trigger iceberg calving, including ocean wave action, collisions with other icebergs, and meltwater accumulation on the iceberg's surface. Monitoring these events using tiltmeters has allowed scientists to link breaking stress near the ice front to storm-generated swells.

What conditions are needed for ice to form in the ocean?

Ocean ice formation requires specific conditions related to water properties and atmospheric influences. For ice to form in the ocean, the sea water must reach its freezing point , which is affected by its salinity. The freezing point of seawater is lower than that of pure water. The growth and decay of sea ice also influences climate through interactions between the atmosphere and ocean. Sea ice influences the exchange of energy between the ocean and atmosphere, and the formation of sea ice generates cold water, which drives the circulation of the world ocean system.

How does snow become glacier ice before it turns into an iceberg?

Snow transforms into glacier ice through a gradual process of compaction and recrystallization. Initially, snowflakes with their intricate shapes, settle and begin to compact under their own weight. The sharp points of the ice crystals evaporate and condense in the hollows, which causes the grains to become more rounded and pack more tightly together. Over time, as the snowpack densifies to 500–600 kilograms per cubic meter, further compression occurs, and recrystallization becomes the dominant process. At a density of approximately 830 to 840 kilograms per cubic meter, the air spaces between the grains seal off, making the material impermeable; it is now called glacier ice. This transition from snow to glacier ice can take anywhere from a few years to thousands of years, depending on the temperature and wetness of the environment. Glacier ice can form icebergs. Most Arctic icebergs come from fast-flowing glaciers from the Greenland Ice Sheet. These glaciers experience stresses that cause crevasses to form, which are then incorporated into the structure of the icebergs.

What causes chunks of glacier to break off and become icebergs?

Icebergs form when chunks of ice break off from glaciers or ice shelves in a process called calving. Several factors can cause this: Stress from the Ice Flow As ice flows from the center of a continent, pressure builds, causing shelves to move seaward. The exposed front of the ice shelf then experiences stress from currents, tides, and ocean swells, leading to fractures and, eventually, icebergs. Wave Action and Collisions Ocean wave action, contact with other icebergs, or the behavior of melting water on the iceberg's surface can also cause calving. Melting and Refreezing Summer meltwater can fill crevasses on the surface of the ice shelf. When this water refreezes, it expands, causing fractures at the base of the crevasses and leading to disintegration. Water Depth The speed of iceberg calving is roughly proportional to the water depth at the terminus.

How do temperature and salt in seawater affect the formation and melting of icebergs?

Temperature and salinity play key roles in both the formation and melting of icebergs. Formation As seawater freezes, pure ice crystals form, and pockets of liquid brine and air become trapped. The amount of salt in seawater is indicated by salinity , which is the amount of salt in grams dissolved in one kilogram of seawater and expressed in parts per thousand. The freezing point of seawater is lower than that of pure water, and its boiling point is higher. Melting Icebergs melt at a rate dependent on the salinity and temperature at various depths in the water column, as well as the iceberg's velocity relative to the water near the surface. Most of the erosion on Antarctic icebergs happens after they emerge into the open Southern Ocean. Meltwater percolates through the weak firn layer, bringing most of the freeboard volume to the melting point.

iceberg

References & Edit History Related Topics

Images & Videos

Map of Antarctica showing major geographic regions such as West Antarctica, East Antarctica, Queen Maud Land, Wilkes Land, Victoria Land, Marie Byrd Land, and Ellsworth Land. The map also marks prominent research stations operated by various countries around the continent's coast and interior, as well as nearby seas including the Weddell Sea, Ross Sea, Amundsen Sea, and Bellingshausen Sea. Surrounding oceans-the Atlantic, Indian, and Pacific-are labeled.

Thematic map of Antarctica highlighting the disintegration of the Larsen Ice Shelf along the Antarctic Peninsula. An inset zooms in on the Larsen A and Larsen B ice shelves, using color codes to show areas of ice shelf loss from January 1995, January 1995 to January 2002, and February to March 2002, alongside the remaining ice shelf as of July 2002. Surrounding seas, land features, and other major ice shelves are labeled for context.

temperature differences between icebergs and ice shelves

Large iceberg floating in the ocean with its white peak rising above water and a much larger blue mass visible below the surface.

At a Glance

iceberg summary

iceberg

ice formation

Written by

Peter Wadhams

Fact-checked by

Britannica Editors

Last updated

Nov. 1, 2026 •History

News •

Giant Antarctic iceberg approaches remote island after three-year journey • Oct. 27, 2026, 12:02 PM ET (Earth.com)

iceberg, floating mass of freshwater ice that has broken from the seaward end of either a glacier or an ice shelf. Icebergs are found in the oceans surrounding Antarctica, in the seas of the Arctic and subarctic, in Arctic fjords, and in lakes fed by glaciers.

Origin of icebergs

Antarctic icebergs

AntarcticaIceberg in the waters off Antarctica.

Icebergs of the Antarctic calve from floating ice shelves and are a magnificent sight, forming huge, flat “tabular” structures. A typical newly calved iceberg of this type has a diameter that ranges from several kilometres to tens of kilometres, a thickness of 200–400 metres (660–1,320 feet), and a freeboard, or the height of the “berg” above the waterline, of 30–50 metres (100–160 feet). The mass of a tabular iceberg is typically several billion tons. Floating ice shelves are a continuation of the flowing mass of ice that makes up the continental ice sheet. Floating ice shelves fringe about 30 percent of Antarctica’s coastline, and the transition area where floating ice meets ice that sits directly on bedrock is known as the grounding line. Under the pressure of the ice flowing outward from the centre of the continent, the ice in these shelves moves seaward at 0.3–2.6 km (0.2–1.6 miles) per year. The exposed seaward front of the ice shelf experiences stresses from subshelf currents, tides, and ocean swell in the summer and moving pack ice during the winter. Since the shelf normally possesses cracks and crevasses, it will eventually fracture to yield freely floating icebergs. Some minor ice shelves generate large iceberg volumes because of their rapid velocity; the small Amery Ice Shelf, for instance, produces 31 cubic km (about 7 cubic miles) of icebergs per year as it drains about 12 percent of the east Antarctic Ice Sheet.

Iceberg calving may be caused by ocean wave action, contact with other icebergs, or the behaviour of melting water on the upper surface of the berg. With the use of tiltmeters (tools that can detect a change in the angle of the slope of an object), scientists monitoring iceberg-calving events have been able to link the breaking stress occurring near the ice front to long storm-generated swells originating tens of thousands of kilometres away. This bending stress is enhanced in the case of glacier tongues (long narrow floating ice shelves produced by fast-flowing glaciers that protrude far into the ocean). The swell causes the tongue to oscillate until it fractures. In addition, on a number of occasions, iceberg calving has been observed immediately after the collision of another iceberg with the ice front. Furthermore, the mass breakout of icebergs from Larsen Ice Shelf between 1995 and 2002, though generally ascribed to global warming, is thought to have occurred because summer meltwater on the surface of the shelf filled nearby crevasses. As the liquid water refroze, it expanded and produced fractures at the bases of the crevasses. This phenomenon, known as frost wedging, caused the shelf to splinter in several places and brought about the disintegration of the shelf.

iceberg

Formation

Melting

News •

Origin of icebergs

Antarctic icebergs

Thank you for signing up!