Iceberg drift

Icebergs float because the density of ice (around 900 kg per cubic meter) is lower than that of seawater (around 1025 kg per cubic meter). The ratio of these densities tells us that 7/8 of the iceberg's mass must be below water. Usually icebergs are 20% to 30% longer under the water than above and not quite as deep as they are long at the waterline.

Large icebergs are controlled mainly by water currents. Winds become more important to icebergs having high sail to draft ratio (otherwise meaning a high ratio between the above water to below water portion). Melting also influences this movement since it can reduce the volume of the sail or above water portion. The drift of an iceberg from its place of origin on the west coast of Greenland to the Grand Banks of Newfoundland takes an average of 2 to 3 years. However, it is possible for an iceberg calved in the Melville Bay area to reach the Grands Banks in the following summer if it remains in the principal southward current for the full period without grounding.

Drift Speeds

The average southward drift rate of icebergs located north of latitude 67N is 1.7 nautical miles per day. Between Cape Chidley and Belle Isle the average drift is 7.6 nautical miles per day.

Drift Numbers

Four factors or conditions primarily determine the number of icebergs that will drift toward and ultimately survive to reach the Grand Banks:

• the intensity or transport rate of the Labrador Current
• the direction,strength and duration of the prevailing winds encountered by the icebergs during this drift
• the extent of the sea ice cover to protect the icebergs
• the environmental conditions to which the iceberg is exposed(air and water temperatures, wave action)