Continental crust is about 20 to 70 km thick and thus 70% of this submerged and oceanic crust being about 10 km thick is only 30 % submerged.
Explanation:
As the hydrological crust is considered to be much denser than the oceanic crust hence at the subduction zones the crusts sink into the mantel and are beneath the lighter continental crust as the oceanic crust is much older than the continental crust. As the continental crust forms many layers and has a bulk composition and the average density is about 2.83 g/cm and has a thickness of about 7 to 10 km.
