SCIENTIFIC RESULTS 115 



ity of the Grand Bank dnring summer and northward on the Luh- 

 rador shelf, as over other bodies of cold water, is usually much 

 warmer at an altitude of a few hundred feet than it is close to the 

 siii'face of the sea. An iceberg which rises a hundred feet or more 

 will form an obstruction to the wind, tending to stir up the air to a 

 I still greater altitude. Around many bergs, therefore, one might 

 I expect the air to be much warmer than in the immediate neighbor- 

 hood, and fact sustains theory, for a surprisingly warm blast of air 

 has often been experienced by the ice-patrol ship when passing close 

 hy and just to the leeward of an iceberg. On the other hand, under 

 (litferent atmospheric conditions, cold air is experienced in the 

 vicinity of the ice. 



Krosion, washing by the waves and ocean swell is most effective 

 of all destructive agents for North Atlantic bergs. The erosion 

 piocesses are always at work from the time the ice drifts any appre- 

 ciable distance out from the juotection of harbors and bays. As the 

 seas continually wash back and forth thev find a crevasse, an irregu- 

 lar shape, or a slight depression, all of which they enlarge. The 

 ceaseless surging of the swell, iDouring back and forth through the 

 small channels, soon erodes valleys, which in turn grow larger and 

 larger, until they develop into the main features of the berg. The 

 inner slopes retreat until only two thin side walls remain, and eventu- 

 ally the valley bottom deepens and disappears below the waves, thus 

 giving the impression of two separate pinnacles or towers of ice. 

 Finally in the later stages of Avasting, far south in the Atlantic, 

 calving and fracture outstrip erosion with the falling of the fragile 

 side walls. Calving is then in turn superseded by melting agencies 

 which turn the last ])age in our iceberg's history. It is interesting 

 to note that the attacks of erosion are always directed at the middle 

 of the mass of ice that is above water. If the sea sculptures too 

 much away from one side, that rcLnon through loss of weight is 

 lifted out of reach of the waves, which then concentrate on the other 

 side, the midsection always receivinir the brunt of the attack. 



During early season around the Grand Bank, February to INIarch, 

 icebergs are subjected to a severe washing by waves wdiich some- 

 times dash completely over them, causing a great deal of wastage. 

 The long ocean swell which makes up during a gale also sets up 

 stiesses and strains in the above-water portion, causing much rend- 

 ing, cracking, and fracture. But only in the small-sized bergs, even 

 in such gales, can one detect a perceptible roll and sway. The ordi- 

 nary run of bergs remain as immovable as the Rock of Gibraltar. 

 Calving begins when the melting and erosive ])rocesses have set up 

 strains that exceed the structural strength of the ice. Prominences 

 and overhanging ledges calve away, sliding down from the steepest 

 ])arts of the berg's sides and slopes. Unequal detachments around 

 the edges interfere with equilibrium and occasionally initiates calv- 

 ing on a major scale. The berg begins to roll slowly and deeply to 

 and fro, and when some bulging prominenc^^ swings far away from 

 the perpendicular thousands of tons of ice rupture to fall, avalanche- 

 like, down to the sea. In the case of many tons of ice, the effect 

 is very curious; it seems to fall much more slowly than really is the 

 case. Stability is, of course, seriously disturbed, and the berg may 

 again suffer one or more successive calvings of its irregular j^arts 



