Icebergs float because of the density difference between ice and water. The fact that roughly 90% of an iceberg is submerged is a direct consequence of this density difference.
Density and Buoyancy
The density of ice is approximately 0.92 g/mL, while the density of seawater is around 1.03 g/mL (slightly higher than freshwater's 1.0 g/mL). This means ice is less dense than water. Because ice is less dense, it floats. The portion of the iceberg submerged displaces a volume of water equal to the iceberg's weight. Since ice is only 92% as dense as water, 92% of its volume needs to be submerged to displace enough water to equal the ice's weight, resulting in approximately 90% of the iceberg being underwater.
Archimedes' Principle in Action
This phenomenon is perfectly explained by Archimedes' principle: a submerged object experiences an upward buoyant force equal to the weight of the fluid it displaces. An iceberg floats when the buoyant force equals the iceberg's weight. Because ice is less dense than water, a larger volume of ice must be submerged to generate enough buoyant force to balance its weight.
Factors Affecting Submersion
While approximately 90% is a good rule of thumb, the exact percentage of an iceberg submerged can vary slightly depending on:
- Salinity of the water: Higher salinity (more salt) means denser water, leading to a slightly smaller percentage submerged.
- Iceberg shape: Irregular shapes can affect the distribution of buoyancy.
- Temperature of the water: Colder water is slightly denser.
Therefore, the commonly cited 90% figure is a close approximation based on the average density difference between freshwater ice and saltwater.
