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 as larger icebergs are moved into warmer water by currents. 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 used by vessels crossing the North Atlantic Ocean between Europe and North America. While most vessels using these shipping lanes have reinforced hulls, icebergs can still be a danger and should be avoided if possible. A large iceberg can be seen from a distance and frequently detected by ship borne radar allowing avoiding action to be taken. However a small growler is still capable of causing costly damage to a ships hull possibly even leading to the sinking of the vessel but their small size makes them more difficult to spot. Dense sea fogs which are formed when cold Labrador current from the North meets the much warmer Gulf Stream from the south often limits visibility in the area adding to the iceberg hazard. This makes the ice warning system a vital safety resource.
Of course icebergs are a hazard in other parts of the world besides the Grand Banks area. For this reason worldwide monitoring of icebergs is carried out by the US National Ice Center which uses polar orbiting satellites to obtain most of their data. The National Ice Center provides ice reports for the Arctic and Antarctic regions as well as Chesapeake Bay and the Great Lakes of North America, in addition to that made by the IIP for the Grand Banks shipping area.