NOTES ON THE igi6 ERUPTION OF MAUN A LOA 479 



of all proportion, either to the outrush of imprisoned gas from this 

 vent (for gas emission throughout the flow was apparently small in 

 volume and relatively very quiet), or to the momentum-pressure 

 of the outpoured magma. Also, the features of the rifting and 

 their distribution appear to differ from those that should be expected 

 to result from such causes. (Resemblances of this action to fissure- 

 eruption phenomena in Iceland are noted below. See especially 

 Plate VI, c, and Figs. 2 and 3.) Moreover, as just mentioned, 

 great numbers of weak to moderately strong local earthquakes 

 were registered at the observatory 30-35 miles from the source of 

 action, the energy of these increasing even after the cessation of 

 forward movements of the flow, but while the vents at the source 



Fig. 2. — A panoramic view looking N.N.E., showing the old red cinder cone 

 riven by new cracks, and the solfatara at the head of the new rift (the figures of the 

 men give scale); and black lava, of 1907, at the base of the cone, which is a little 

 over 100 feet high. 



were still freely open. Several of these were felt definitely over a 

 considerable area, having a radius of much more than 30 miles; 

 and one or two of these were quite sharp at the observatory. The 

 question of their origin will be discussed in a later paper. 



In brief, for many reasons the conception that this eruption 

 was, in part at any rate, primarily a tectonic event must be examined 

 thoroughly and not put lightly aside. No very violent action was 

 observed or suggested, nor any such as would be expectable were a 

 rift like this to be produced by explosive forces, or by upthrust 

 from a confined substance tending to expand rapidly or seeking 

 immediate outlet to the surface — as volcanic potential usually is 



