470 0. D. von Engeln — Studies on Ice Structure. 



Under these conditions of progressive granular growth it is 

 readily perceivable how the segregation of pure ice nuclei 

 from the saline interstitial films takes place. Moreover, on the 

 basis of the evidence stated above it seems unlikely that the 

 body temperatures of glacier ice are very low. Hence, with 

 only the development of comparatively slight pressures, 

 through continued accumulation of snow above, it would appear 

 that the growth of granules would be much facilitated and the 

 flow of the ice initiated. That ice can be completely recrystal- 

 lized under comparatively moderate pressures (1400 lhs. per 

 sq. in. or less ; equivalent to an ice column about 3500 feet 

 high) at air temperatures a number of degrees below the freezing 

 point (— 4°F. to 20°F.) was shown by the compression experi- 

 ment with the unyielding copper cylinder. Moreover, the crys- 

 tals developed were of quite large size showing that the velocity 

 of the reaction is great; in other words, large crystals can grow 

 in a short time. The permanent deformation by flow of the 

 ice cubes under pressures approaching their crushing strength 

 (650 to 1000 lbs. per sq. in., equivalent to an ice column 1600 

 to 2500 feet high) clearly demonstrates the ability of ice to 

 yield plastically under differential pressure without disintegra- 

 tion and at temperatures a number of degrees below the pres- 

 sure-melting point. Such yield may be in part due to shear, 

 but in accordance with the known properties of the ice crystals 

 can be more certainly ascribed to internal liquefaction in the 

 planes of the basal gliding plates. The cause of this readier yield 

 or gliding in the basal planes in turn may find its explanation 

 in the presence of a residuum of saline material between the 

 basal plates of the crystal as argued by Buchanan and Quincke. 

 Another possibility is that it is due to an increase, under pres- 

 sure, in the volume of water molecules (H 4 2 ) included with 

 the polymerized ice molecules (H 6 3 ) in the solid phase, ice, at 

 temperatures near the transition point, with consequent lessened 

 viscosity or internal friction between the crystalline particles. 

 "Whatever the explanation, it is clear that such yield would 

 account for the continuous deformation of even quite cold ice 

 at great depths below the surface in the bottom zones of 

 large glaciers. 



That the lubricating effect of the saline interstitial films, 

 increased in volume under pressure, and of the plastic internal 

 yield described above, amply suffice to promote the free flow 

 of ice without loss of coherence, was proved by the experiment 

 in which the ice rod was caused to emerge from the lateral 

 orifice of the rod cylinder to a total length of 16 inches. 



Moreover, the fact, that, while at the beginning of the flow 

 the temperatures were low, pressure relatively high and the 

 emergence slow, in its later progress when pressures were 



