Sue Long of North is absolutely correct in her observation that as ice cubes floating in a glass of water melt, the water level remains unchanged. This is a nice demonstration of one of the consequences of Archimedes’ Principle, namely that a floating object displaces its own weight of the liquid in which it is floating. There is an old "party trick" in which one puts some ice cubes in a glass, fills the glass with water to the brim and then asks an unsuspecting dupe if the water will overflow as the ice melts. Since the floating cubes rise above the brim, the unwary victim, ignorant of Archimedes, expects that an overflow will occur.
So much for the physics of floating objects. Glaciers are not floating objects; these great rivers of ice lie on land; either their melted waters flow to the sea along rivers, or, for those glaciers which terminate at the coast, enormous chunks of ice break off (the technical term is "calve"), fall ...
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