How do icebergs form?
Icebergs are blocks of fresh-water ice that break off from glaciers and float out to sea. Glaciers are formed in polar regions where snowfall lasts for centuries, or even millennia, without entirely melting, and is eventually compressed into ice.
In the North Altantic, most icebergs originate from the tidewater glaciers of Western Greenland. Compressed snow becomes firm, a granular snow, transformed eventually by pressure into a dense ice. The weight of the icecap builds, causing the ice to flow as much as 60 feet a day through openings in the coastal mountains. Rising and falling tides cause slabs of ice to break off and form moving "rivers of ice".