114 



bergs during certain months from grounding along the North Ameri- 

 can coast north of Cape Race, and so ehminating themselves from 

 southern waters. Whether this be true or not, it is an undeniable 

 fact that the field ice tends to keep the surface water about it ice 

 cold. A berg surrounded by field ice in the Labrador Current until 

 it is south of the forty-fifth parallel is conserved much as a cargo of 

 meat is conserved in a refrigerating vessel that is steaming through 

 the Tropics. 



But the field ice prolongs the life of the bergs in another way than 

 through its great cooling effect. In addition it effectually prevents 

 the development of wave motion, and in this way protects most 

 efficiently the vulnerable waterlines of bergs from the washing and 

 melting attacks of moving surface water. 



Calving most frequently takes place by the dropping down of ice 

 masses that overhang an. undercut water line, and so is closely related 

 to surface water attacks. Calving upwards from the smoothly 

 rounded underwater portions of a berg is exceptional in the ice patrol 

 regions. Sometimes a projecting spur that is mostly submerged is 

 broken off by stresses arising from the rise and fall of the swell. 

 These stresses are very large at times, and so are the blows of the sea 

 against a berg's sides. Bergs are usually very dead in the water and 

 take the full force of the seas like rocks. They do not normally roll 

 or ride over the seas like well-designed ships do when drifting. 



Calving generally involves but a very small portion of the mass of 

 a berg at any one time. Of course bergs sometimes break up into 

 two nearly equal parts, but in fully 90 per cent of the cases the amount 

 of ice involved in a calving is so small in comparison with the mass 

 of the berg that equilibrium is only slightly afi^ected. This is the 

 case, even when the meaning of calving is restricted to production of 

 ice volumes of more than 1 ton. The breaking off of small pieces is 

 very frequent under some conditions, and this production of small 

 amounts of ice in the form of chips and tiny blocks is not considered 

 real calving, such as is contemplated here. 



It is reasonable to suppose that the chances of calving and rolling 

 will be much greater in warm water than in cold, but it must be 

 remembered that the conditions will vary much with each individual 

 berg. To venture an opinion for the benefit of those who in the future 

 may be called upon to work upon bergs for any purpose, it is esti- 

 mated that the average berg south of the forty-fourth parallel can 

 be expected to have natural calvings involving the falling off of over 

 1 ton of ice about three times a day, and to experience changes of 

 position involving the turning about an axis more than 60° in less 

 than one minute of time about twice a week. The above is only a 

 rough estimate, based on comparatively few observations. Some 

 bergs wiJjoo;|~.ealve for days at a time and will never turn over until 



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