by Alison Bowler

Created on: July 28, 2008   Last Updated: January 10, 2009

Icebergs are floating chunks of frozen fresh water. They are formed in the polar regions when blocks of ice break free from their parent ice shelf in a process called calving. Once detached from the ice shelves, icebergs can be moved into warmer latitudes by oceanic currents. This movement inevitably brings icebergs into busy shipping lanes and the monitoring of the movement and quantity of icebergs is an important safety factor for the global shipping industry.

After the RMS Titanic sunk in the North Atlantic in 1912, having hit an iceberg, the International Ice Patrol (IIP) was set up to monitor and report icebergs drifting into shipping lanes within the Grand Banks Region of the North Atlantic. The IIP, although it is part of the US coastguard service, is funded by the many countries whose ships regularly use the Grand Banks shipping lanes. They make regular reports of ice hazards which are available to all ships in the danger area.

As part of its' ice reporting service the IIP has set up an internationally recognised naming system based on the size of icebergs. Growler is the term given to the smallest classified iceberg; it is defined as being less than 3 feet high above the water and less than 16 feet long. Very small considering the tallest iceberg seen in the northern Atlantic was measured at 550 feet above sea level and one calved from the Ross Ice Shelf in Antarctica was measured as 183 miles long and 23 miles wide. As most of an iceberg is below water the total height of a growler can be over 20 feet.

The other names used by the IIP in the size classification for icebergs are bergy bits 3-13 feet high, 15-46 feet long; small 14-50 feet high, 47-200 feet long; medium 51-150 feet high, 201-400 feet long; large 151-240 feet high, 401-670 feet long and very large which are greater than 240 feet high and greater than 670 feet long. They are also classified according to shape; these classifications being tabular, domed, wedge, pinnacle, block and dry-dock which has eroded to form a water filled slot or channel. The use of internationally recognised descriptive classifications has allowed scientists to plot the movement of individual icebergs from sightings made from various ships and planes. From these plots, made over many years, ice warnings can be given to ships traversing the North Atlantic allowing them to be aware of ice hazards in their area.

Growlers are formed by the breaking up of large icebergs, calving from ice shelves and the inevitable melting

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