Icebergs floating on sea water are dangerous for ships. Explain the reason.

Density of ice (0.9 g cm^-3) is less than the density of sea water (1.02 g cm^-3). So, an iceberg floats in sea water with its large portion submerged inside the water and only a little portion of it is above the surface of water. Thus, a ship can collide with the invisible part of the iceberg under the surface of water. Hence, it is dangerous.