Finding the age of the ice Ice Cores are cylinders of ice drilled out of ice sheets or glaciers. They can be several thousand metres long in total, although they are cut section by section. Since snow falls each year, and contains trapped gases, chemicals and dust, chemical analysis of the core yields information on climate and man's effect on the environment. Information going back half a million years has been obtained. Icebergs float Icebergs float, by Archimedes' principle, because the density of ice is less than that of water.
Icebergs can be 'calved' from ice shelves if an ice shelf warms up and deep ice cracking occurs.
Ice cracks are usual in summer in polar regions, but the calving of the glacier from the Larsen ice shelf in 1995 was unusual, and accompanied other forms of disintegration of the shelf. It was due to recent warming trends in the area. It was an iceberg which sank the Titanic on its maiden voyage. You can find links to many sites by looking at the Smithsonian site. If you wonder why the Titanic was made of such flimsy materials try looking at the site with the properties of the metals from which the Titanic was constructed.