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Buoyancy When floating ice melts, does water level rise?
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Buoyancy
When floating ice melts, does water level rise?
When floating ice melts, does the water level rise?
Seed Expert Claude Baudoin writes:
Water expands when it freezes, so you might think that when it melts and reduces in size, the water level will go down. Alternatively, because part of the ice floats the water, you might think that when it melts, the water level will rise.
Neither is true, as explained by Archimedes principles.
When an ice cube (or an iceberg, which is a big ice cube) floats in water, then by definition the weight of the ice cube is exactly equal to the buoyancy force, which is equal to the weight of the displaced water.
When the ice cube melts, its volume changes, but its weight is conserved (law of the conservation of mass). So the melted water from the ice cube has exactly the same weight as the water that was displaced by the ice cube when it was frozen -- therefore the volume of melted water fits exactly in the previously displaced volume -- and the water level stays the same.
Note that this argument applies only if the ice cube is made of the same water as the water that it is floating in. This is true, for example, with the Arctic ice pack, which is made of frozen sea water. However, it is not true for Antarctic icebergs, which are blocks of fresh-water ice from the continent that are floating in salt-water sea. In this case, we must take into account that the salt water is denser than the fresh water. The fresh-water iceberg still weighs as much as the weight of the displaced salt water, but because of the difference in density, the volume of melted fresh water will be slightly greater than the displaced volume of salt water -- so when the iceberg melts, the water level will rise, although the difference is very small.
If the ice is melting due to a rise in temperature of the water, then the water level might rise because of thermal expansion - related to, but not because of, the ice melting.
If the ice was totally or partly supported on the bottom of the vessel (or sea), then when it melts the water level will certainly rise. In the limit, if there was no water in the vessel at the start of the experiment, there clearly will be at the end, and it is obvious the water level has risen. This is a key problem resulting from global warming – melting ice that was covering land areas such as Antarctica and Greenland is adding to sea levels.
To learn more about buoyancy, try the SEED Buoyancy experiment.
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