Great explanation Glasso! It is worth mentioning that this fact is described by the Archimedes's principle. In this particular case, buoyant force Fb acting on around 90% of the iceberg balances gravity force Fg on the iceberg. More precisely, from Fb = Fg if follows ρ * g * (V / x) = m * g where is the density of water, g gravitational acceleration, V is the volume and m mass of the iceberg. A short calculation gives result.