Tip of the iceberg....

[xoxoxoBruce]

From here

Usually 1/8th of an iceberg is above the waterline. That part consists of snow, which is not very compact. The ice in the cold core is very compact (and thus relatively heavy) and keeps 7/8ths of the iceberg under water. The temperature in the core is constant: between -15 and -20 degr. Centigrade. An iceberg that has tumbled over several times, has lost is light snow layers and so the iceberg gets relatively heavier then before (with the snow) and because of the greater compactness, only 1/10th rises above the surface.