Icebergs are a mass of ice that has become detached, or calved, from the edge of an ice sheet or glacier and is floating on the ocean. Because ice is slightly less dense than water about one ninth of the total mass of a berg projects above the water.

Icebergs differ from other ocean ices: sea ice is formed directly from the freezing of ocean water; pack ice is tightly packed fragments of sea ice; ice floes are small, floating ice fragments that separate from pack ice. Fast ice - is ice attached to a shore.

Icebergs are mostly white because the ice is full of tiny air bubbles. The bubble surfaces reflect white light giving the iceberg an overall white appearance. Ice that is bubble free has a blue tint which is due to the same light phenomenon that tints the sky.

The bluish streaks of clear, bubble free ice often seen in icebergs results from the refreezing of meltwater which fills crevasses formed in the glacier as it creeps over land. The ice is blue because of the natural light scattering characteristics of pure ice. Occasionally airborne dust or dirt eroded from land ends up on the glacier surface eventually forming a noticeably darkened brown or black layer (in any orientation) within the ice of a floating iceberg.

Greenland is the source of most of the icebergs in the N Atlantic, where the iceberg season lasts roughly from February to October. Greenland and other N Atlantic icebergs are usually peaked and irregular in shape; Antarctic icebergs are tabular, with flat tops and steep sides.

Before the development of radar, sonar, and the Global Positioning System, sailors on watch in the Arctic region would listen for distinctive sounds to help them determine whether icebergs were close or far away.

As a consequence of the loss of the Titanic through collision with an iceberg in 1912, a patrol of N Atlantic shipping channels was initiated in 1914 by the international agreement of 16 nations.

Patrols use planes and surface vessels equipped with radar, loran, and underwater sound equipment. A constant census of bergs is maintained, and the location of an iceberg is reported to any ship in its vicinity.

A fantastic variety of shapes result from the deterioration process of icebergs. Despite the fact that no two icebergs are the same, there are certain categories of shapes that are used for iceberg observation. Often the terms; tabular, blocky, wedge, dome, pinnacle, and drydock are used.

For those who wish to look beyond the beauty of icebergs there are many things to look for which can make iceberg watching more interesting. Besides estimating the iceberg's size and shape there are many features which may be noted. Colored streaks, caves and tunnels, old and new waterline notches, even objects such as boulders or birds are seen on icebergs. Even more spectacular is the occasion of an iceberg calving and rolling which can often be heard from a good distance.