Icebergs are large chunks of ice that break off from glaciers. This process is called calvin. Icebergs float in the ocean, but are made of frozen freshwater, not saltwater.

Most icebergs in the Northern Hemisphere break off from glaciers in Greenland. Sometimes they drift south with currents into the North Atlantic Ocean. Icebergs also calve from glaciers in Alaska.

In the Southern Hemisphere, almost all icebergs calve from the continent of Antarctica.

Some icebergs are small. Bergy bits are floating sea ice that stretch no more than 5 meters (16.5 feet) above the ocean. Growlers are even smaller.

Icebergs can also be huge. Some icebergs near Antarctica can be as big as Sicily, the largest island in the Mediterranean Sea. As little as one-eighth of an iceberg is visible above the water. Most of the mass of an iceberg lies below the surface of the water. This is where the phrase "tip of the iceberg" came from, meaning only part of an idea or problem is known.

There are many different kinds of icebergs. Brash ice, for instance, is a collection of floating ice and icebergs no more than 2 meters (6.5 feet) across. A tabular berg is a flat-topped iceberg that usually forms as ice breaks directly off an ice sheet or ice shelf.

The ice below the water is dangerous to ships. The sharp, hidden ice can easily tear a hole in the bottom of a ship. A particularly treacherous part of the North Atlantic has come to be known as Iceberg Alley because of the high number of icebergs that find their way there. Iceberg Alley is located 250 miles east and southeast of Newfoundland, Canada.

In 1912, the Titanic, a large British ocean liner on its way to New York, struck an iceberg and sank in Iceberg Alley. More than 1,500 people drowned. Soon after the Titanic sank, an International Ice Patrol was established to track icebergs and warn ships. That patrol continues today.

Iceberg patrols now use global positioning system (GPS) technology to help locate icebergs and prevent more tragedies like the Titanic. In 1999, the National Ice Center lost track of an iceberg the size of Rhode Island. It was found drifting toward the Drake Passage, an important shipping route south of Argentina. Dr. David Long of NASA's SeaWinds science team used satellite data to track the iceberg, the first time satellite technology was used for that purpose. Since that time, the SeaWinds team has used satellites to track the world's ice.

Icebergs that drift into warmer waters eventually melt. Scientists estimate the lifespan of an iceberg, from first snowfall on a glacier to final melting in the ocean, to be as long as 3,000 years.

iceberg
Antarctica and Greenland, home to the world's ice sheets, are the chief source of the world's icebergs.

Why So Blue?
Some glaciers and icebergs are blue, for the same reason water is blue. The chemical bond between oxygen and hydrogen in water absorbs light in the red end of the visible light spectrum.

Blue glaciers and icebergs are not blue for the same reason the sky is blue. The sky is blue due to atmospheric scattering of light (Raleigh scattering), a different phenomenon.

Iceberg Prose
The American novelist Ernest Hemingway is famous for his writing style of short sentences. Hemingway, in fact, compared his writing style to icebergs. Just like an iceberg remains largely unseen beneath the surface, a writer can leave parts of a story unwritten. Hemingway believed the reader would understand and be affected by the unwritten parts of a story as well as parts that were actually written.

bergy bit
Noun

sea ice floating not more than 5 meters (16.5 feet) above the ocean, and not more than 10 meters (33 feet) across.

brash ice
Noun

floating fragments of ice and icebergs no more than 2 meters (6.5 feet) across.

calving
Noun

process where a glacier cracks and breaks apart.

Noun

one of the seven main land masses on Earth.

Noun

steady, predictable flow of fluid within a larger body of that fluid.

data
Plural Noun

(singular: datum) information collected during a scientific study.

Ernest Hemingway
Noun

(1899-1961) American author and journalist.

estimate
Verb

to guess based on knowledge of the situation or object.

freshwater
Noun

water that is not salty.

Noun

mass of ice that moves slowly over land.

Global Positioning System (GPS)
Noun

system of satellites and receiving devices used to determine the location of something on Earth.

growler
Noun

small chunk of floating sea ice, extending less than one meter (3.3 feet) above the ocean, and fewer than five meters (16 feet) in length.

Noun

water in its solid form.

Noun

large chunks of ice that break off from glaciers and float in the ocean.

Iceberg Alley
Noun

area in the North Atlantic Ocean with a large number of icebergs.

Noun

thick layer of glacial ice that covers a large area of land.

ice shelf
Noun

mass of ice that floats on the ocean but remains attached to the coast.

Noun

body of land surrounded by water.

lifespan
Noun

length of time from when an organism is born to when it dies.

ocean liner
Noun

large ship used to transport people or goods to and from ocean ports on established routes, or lines.

satellite
Noun

object that orbits around something else. Satellites can be natural, like moons, or made by people.

shipping route
Noun

path in a body of water used for trade.

snowfall
Noun

amount of snow at a specific place over a specific period of time.

tabular berg
Noun

flat-topped iceberg, usually formed by ice breaking off from an ice shelf.

Titanic
Noun

luxury cruise ship that sank in the North Atlantic Ocean in 1912.

treacherous
Adjective

very dangerous.