124 MARIOX EXPEDITION TO DAVIS STRAIT AND BAFFIN BAY 



first explosion occurred during a dense fog which shut off all view, 

 but repeated heavy calvings were heard from time to time following 

 the blast. Another mine suspended from one side to a depth of 10 

 feet brought down much loose ice, but a second charge placed at 20 

 feet below the surface of the water jarred the berg most of all. The 

 last mine, being against the side wall of the berg at a depth of 30 feet, 

 detached great quantities of ice, causing the berg to rise and then fall 

 sideways and to break squarely in two at the point where the mine 

 had been placed.*'^ Gunfire has no material effect, but only shakes 

 :lown a few tons of ice from the point of impact. 



The Effect of Explosives on icebergs 



Figure 83. — On June 5, 1923, the U. S. Coast Guard cutter Modoc exploded four 

 50-pound gun cotton mines suspended from this berg at a depth of 00 feet. The 

 berg was observed to quiver perceptibly the instant of the explosion, and .several 

 growlers were detached from the main body, but no other results were observed 

 nor did the berg change in equilibrium. (Official photograph, international ice 

 patrol.) 



The melting of icebergs induces a circulation of the water in which 

 they float. Pettersson (1904, p. 286) and Sand.strom (1915, p. 245) 

 found by laboratory experiments that fre.sli ice melting in a tank 

 of salt water tends to induce three currents: (1) A cold surface cur- 

 rent of low salinity away from the ice; (2) an intermediate current 

 of relatively warm salty water toward the ice; and (3) a cold cur- 

 vent sinking diagonally away from the ice. Pettersson in several pub- 

 lications has offered these experiments as an explanation for many 

 of the circulatory features of the world's oceans. Barnes (1910) as 

 a result of ice investigations in the St. Lawrence River believes that 

 the detection of such movements around bergs by means of precise 



^'^ Zeusler (1925, p. 41) gives a good description of mining operations as occasionally 

 carried out by the ice patrol. 



