NOTES ON THE iqi6 ERUPTION OF MAUN A LOA 335 



generally results from fragmentation or granulation in the course 

 of flows of lava grown too stiff for further plastic flow under the 

 prevailing conditions — whether this results from rapid cooling due 

 to rapid escape of gas, to slow cooling, or to stiffening due to the 

 development of crystalline phases, throughout the mass, or in 

 lumps so as to form a sludge. The time is not ripe for discussion 

 and comparison of all these factors and their interrelationships. 



But the action described above, with suitably conceived modi- 

 fications applicable in the region of more rapid streaming, and 

 where greater masses and higher temperatures are involved, 

 appears to the writer to be capable of explaining most of the vagaries 

 of surface texture and miniature surface forms exhibited by a-a in 

 Hawaii. Everything that the writer has seen in connection with 

 this outbreak, and all the reports that have come to his attention, 

 indicate that there was no excessive evolution of volcanic gases from 

 the molten lava on this occasion; and all indications are that the 

 temperature of the melt has not been excessively high. This points 

 to a relatively cool and viscous fluid. And so far this supports the 

 view of its action sketched here. It is, of course, not unlikely that 

 still other mechanisms are involved in the forming of a-a, and 

 emphatically there is no disposition to question any which rest 

 upon observation or sound rationale. However, to the writer it 

 seems unnecessary to appeal to unobserved, recondite, special 

 mechanisms to explain the fragmentation and textural qualities 

 of a-a. This view is in accord with the tenor of a view expressed 

 to the writer by Dr. William T. Brigham, of the Bishop Museum 

 in Honolulu, that a-a is the slush ice, or floe ice, in a cooled and 

 freezing stream (the granulation by motion of a stiff, overcooled 

 fluid on the point of solidifying). This seems the best short 

 expression of the idea. 



The writer saw the action just as the stream had slowed up, 

 almost undoubtedly on account of failing supply at the source of 

 this branch. Thus the failure of pressure from above and the 

 radiation of heat all along the course led to rapid increase of 

 sluggishness. At this stage of the flowing there was practically no 

 gas action at the front. Blue fumes were rising from the surface, 

 along with heat-disturbed air, but these were so thin that from a 



