Polar Icebergs

Icebergs are made of frozen fresh water and are found in the oceans of both the Northern and Southern hemispheres. They break off from the Polar and Greenland ice shelves in a process called calving. After being calved from an ice sheet, oceanic currents carry the icebergs into warmer latitudes by where they can be a danger to shipping.

After the RMS Titanic sunk in the North Atlantic after hitting an ice berg in 1912 the International Ice Patrol, part of the US Coastguard Service, was set up to monitor and report icebergs drifting into shipping lanes in the Grand Banks Region of the North Atlantic. As part of this reporting service, they set up a 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 than long. Very small considering the tallest iceberg seen in the northern Atlantic was 550 feet above sea level and one calved from the Ross Ice Shelf in Antarctica measured 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 size classifications for ice bergs 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 being tabular, domed, wedge, pinnacle, block and dry-dock which has eroded to form a water filled slot or channel. The use of internationally recognized descriptive classifications allows 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 are issued to ships traversing the North Atlantic.

Growlers are formed by the breaking larger icebergs, calving from ice shelves and the inevitable melting as currents move larger icebergs into warmer water. They are the last stage in the life of an iceberg, which could have calved from an ice shelf several years before.

During the ice season, which in the Grand Banks area is usually between February and July, icebergs calved from the Greenland ice shelf are moved south by the fast moving Labrador current. This brings the icebergs into the major shipping lanes crossing the Atlantic between Europe and North America. A large iceberg is visible from a distance and frequently detected by ship borne radar allowing avoiding action to be taken. While most vessels crossing an area of ice hazard have reinforced hulls, a small growler is still capable of causing costly damage to a ships hull possibly even leading to sinking of the vessel but their size makes them difficult to spot. Dense sea fogs which are formed when cold current from the North meets the much warmer Gulf Stream from the south adds to this hazard.

The US National Ice Center carries out worldwide monitoring of icebergs using polar orbiting satellites to obtain most of its data. This provides ice reports for the Arctic and Antarctic as well as Chesapeake Bay and the Great Lakes of North America, in addition to that made by the International Ice Patrol in the grand Banks shipping area. The break up of the winter ice forms the icebergs found in the Great Lakes of North America.