The Track of an Iceberg

iceberg tracks

Once an Arctic iceberg has been calved and moves out to the open sea, it sojourns in Baffin Bay for three months to two years, during which time it undergoes some disintegration through melting and calving of small chunks of ice from its perimeter. This results in a decrease in mass of about 90 percent by the time it reaches the coast of Newfoundland and the Grand Banks in the North Atlantic. When the iceberg enters the region of the Grand Banks, where the warm waters of the Gulf Stream meet the colder waters of the Labrador Current, it has only a few days of life remaining.

A large iceberg 120 metres long melted within 36 hours in 27 C (80 F) water. The estimated rate of iceberg melting is based on the observations of a number of individuals from the International Ice Patrol. For mild sea conditions an iceberg deteriorates at a rate of height decrease of two metres per day in 0 to 4 C (32 to 39 F) water, and three metres per day in 4 to 10 C (39 to 50 F) water. Destruction of icebergs in warm water is increased during stormy weather, when mechanical erosion of icebergs is added to the thermal effects of air and water. During the erosion process icebergs usually take on the form of a saddle, because erosion at one pole of the major axis of the iceberg results in that point rising, while the other end of the major axis is being eroded. Subsequently the latter end, owing to loss in weight, arises, and this rocking back and forth continues while constant erosion is occurring along the minor axis leading, usually, to a bipeaked or saddle-shaped structure.

The western shore of Greenland has the fastest-flowing glaciers on the Earth. The one known as the Quarayaq Glacier flows at a velocity between 20 and 24 metres per day, greater than the velocity of most Alpine glaciers. Jakobshavn Glacier at latitude 70 N, approximately, produces 10 percent of all the Greenland icebergs (approximately 1,350 annually) and flows at about 20 metres per day. The icebergs accumulate in a fjord and periodically spill from this fjord in groups accompanied by noise that can be heard for several kilometres. This greatest iceberg-producing glacier measures only 7 kilometres along its front and is 90 metres above sea level. In contrast to the rapidly moving glaciers, the very wide glaciers that move slowly produce only very small icebergs. Some glaciers, such as the Frederikshåb, Greenland, with a 33-kilometre front, have rates of flow equal to the rate of melting, and thus produce no icebergs. The annual yield of icebergs in the Arctic is, at the most, 15,000, with only 5,000 or so of sufficient size to reach the open ocean intact.

The largest glacier in the Northern Hemisphere is the Petterman Glacier, at 81 N 62 W. Although it is only a few metres above seawater, its ice foot extends as far as 40 kilometres out to sea, and it pushes a path through old piled-up sea ice. These long fingers of glacier ice, under severe climatic conditions, break off once every 10 to 20 years. Another glacier of importance is the Jungersen Glacier in northern Greenland. This glacier and the Petterman Glacier produce very large tabular icebergs, known in the Arctic as "ice islands." They are similar in shape and mode of formation to the large tabular icebergs of the Antarctic but are much smaller.

East Greenland icebergs tend to move southward; they are small and few in number. The icebergs that do leave the fjord and the coast area enter the East Greenland Current, and some join the West Greenland icebergs. The icebergs that reach the North Atlantic Ocean from northern Greenland, Siberia, and the Northwest Territories constitute less than 10 percent of the total icebergs produced in the Northern Hemisphere. They do not affect the sea routes and, other than their formation of ice islands, have no importance to humans. Most icebergs originating from western Greenland are of great importance; of an annual production of about 7,500 bergs (Arctic total is 10,000-15,000), the Labrador Current carries 800 to 1,000 into the open ocean.

Of the 10,000 to 15,000 icebergs calved from glaciers annually in the Arctic, only 375 on the average pass Newfoundland, or latitude 48 N, into the North Atlantic Ocean. In some years more than 1,000 are seen, in others fewer than 30. The yearly average diminished over 20 years until 1972, when 1,400 icebergs were sighted south of 48 N in the North Atlantic.


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