274 



Ice in the Sea 



part of the glacier and rise as icebergs to the surface ; this leaves the edge of the glacier 

 unchanged. The largest icebergs are produced by the first type: under the influence 

 of the further continuous supply in ice mass the glacier pushes out into the sea for 

 200-300 m depending on the morphology of the fiord bottom ("fore part of glacier"). 

 The fiord water slowly penetrates into the projecting ice mass and, due to buoyant 

 forces, the forehead of the glacier gets lifted until it finally breaks off. Calving usually 

 occurs exactly there where the depth of the fiord has increased to such a rate that the 

 forward pushing ice-tongue loses contact with the sea bottom and starts floating. In 

 addition to the increasing buoyancy, lifting due to the tides may also upset the equi- 

 librium in the glacier tongue. Presumably the formation of icebergs proceeds in the 

 same way in the Antarctic; however, the process there is of much larger dimension and 

 produces enormous flat-topped icebergs. 



The direct production of icebergs proceeds at about the same rate throughout the 

 year, but the number of icebergs reaching the open sea depends on the nature of 

 the fiord and more especially on the season of the year. In winter the fiords are frozen 

 and the icebergs are trapped. They are released with the coming of summer, all within 

 a short time and mostly all at once, and they then drift away. This gives rise to the 

 so-called ""iceberg swarms'" which often occur in Baffin Bay and Davis Strait, 



The shape of icebergs is remarkably variable: the pure-chance forms after calving 

 are remodelled by the action of sea waves and by melting above and below the water; 

 classification of these diff"erent forms is thus rather pointless. The height of icebergs 

 varies widely, but the largest are of course found in the area where they are formed. 

 Measurements made by Drygalski on eighty-seven icebergs frozen into the sea ice in 

 the East Greenland fiords gave the results shown in Table 106. 



Table 106 



The height decreases rapidly after their formation. The highest iceberg measured by 

 the International Ice Patrol Service south of Newfoundland was 80 m high; it was 

 flat-topped and 517 m long. Its volume was estimated as about 25-5 milUon m^. 

 According to Smith, the icebergs in the Davis Strait have an average volume of 1-5 

 milUon m^; those of the Newfoundland Banks between 0-1 and 0-15 million m^; 

 they are about 30 m high. The ''depth of immersion'' of an iceberg depends on the 

 specific weight of glacier ice. Since icebergs contain a large percentage of air and 

 numerous cracks and holes this depth does not correspond to that calculated solely 

 from the specific weight. For mean densities of 0-8997 for the ice and 1-02690 for 

 polar water, flat-topped icebergs will have one-eighth of their volume above the surface 

 of the sea and seven-eighths will lie below the surface, but the shape of an iceberg 

 has a considerable effect on the depth to it which immerses. Smith has made a summary 

 of direct measurements and has found that for the most peculiarly-shaped icebergs of 

 of the north-western Atlantic the ratio is 1 : 3, The flat-topped Antarctic icebergs 

 immerse to greater depths. 



