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• Loss of the Titanic to an iceberg

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.) 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.

The process of icebergs breaking off of a glacier is called calving. Icebergs consist of freshwater ice, pieces of debris, and trapped bubbles of air. The combination of ice and air bubbles causes sunlight shining on the icebergs to color the ice spectacular shades of blue, green, and white. Icebergs come in a variety of unusual shapes and sizes, some long and flat, others towering and massive.

An iceberg floats because it is lighter and...