Icebergs
An iceberg is a large mass of free-floating ice that has broken away from a glacier. Glaciers are flowing masses of ice, created by years of snowfall and cold temperatures. Icebergs are made of freshwater ice and not of frozen sea water. They form from the edge of glaciers when the glacier reaches the sea and either breaks off in pieces to form an iceberg, or in the case of an ice shelf, begin to float on the sea and then breaks off from the rest of the glacier as a large slab. Beautiful and dangerous, icebergs are carried about the ocean surface until they melt. Most icebergs come from the glaciers of Greenland or from the massive ice sheets of Antarctica.
So what criteria must a chunk of ice meet to officially be called an iceberg? By definition, icebergs are at least seventeen feet proud of the water and fifty feet long. Anything smaller is called a growler or bergy bits. One of the biggest Greenland bergs ever reported by the Coast Guard was 550 feet above the sea. Icebergs in the Arctic regions are formed from mountain glaciers fed by the Greenland ice sheets and are high and narrow, with above-water shapes resembling towers; these are called castle bergs. Large tabular icebergs are found at the ice shelves of Antarctica. One large tabular Antarctic iceberg in 1987 was reported to be 100 miles long, 25 miles wide and 750 feet thick.
The day-to-day movement of an iceberg is controlled by the size and shape of the iceberg, previous and present wind, surface wind current, and general ocean current. The most important factor in assessing wind drift of icebergs is size and shape. Winged icebergs, those with sail-like pinnacles around the central mass, are very much influenced by the winds and move at speeds of one knot (24 nautical miles, or 44 kilometers, per day) under the influence of steady winds of 30 knots. The momentum of icebergs is so great that once in motion they continue for hours after the wind has abated.
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