SEED Science

When floating ice melts, does water level rise?

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When floating ice melts, does water level rise?

When floating ice melts, does the water level rise?


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 in the water, you might think that when it melts, the water level will rise. Actually, neither is true, as explained by Archimedes' principle.

Does the volume of water change when ice melts?

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 buoyant force, which is equal to the weight of the displaced water.

When the ice melts, its volume changes, but its weight is conserved (law of the conservation of mass). So the melted water from the ice has exactly the same weight as the water that was displaced by the ice when it was frozen. Therefore, the volume of melted water fits exactly in the previously displaced volume and the water level stays the same.

Different types of water and ice

If the ice is made from water that is different from what it is floating in (for example, a fresh water iceberg floating in salty ocean water), a very small rise in the water level might be seen. Another situation in which the water level might rise a little is if the water is warming up (which helps to melt the ice as well). In this situation, the slight rise in the water level is due to the thermal expansion of the water.

Try it yourslef with PlanetSEED's the ice melting experiment Cork in Ice experiment on PlanetSEED. To learn more about buoyancy, try the interactive game Buoyancy Explorer.