58o 



CLARENCE N. FENNER 



vents, however, would tend to be concealed by the material that 

 they themselves extruded and by later materials from the ash- 

 falls, and we are not able to point out the exact location of such 

 vents with certainty. It is rather by a process of deduction that 

 our opinions as to their position have been reached/ 



The vents of extrusion may well have been located along the 

 fissures that are now the seats of fumarolic activity. Support is 



Fig. 9. — Carbonized stumps and tundra. The foreground was covered by the 

 sand-flow, but the standing trees in background were beyond its reach. Photograph 

 by E. G. Zies, 1919. 



given to this supposition by evidences of former more vigorous 

 activity of a mildly explosive kind at some of these localities. 

 Possibly the newly formed crater of Novarupta in the upper part 

 of the valley was one of the vents, differing from the others only 

 in that it was of larger size than most and that its activity con- 



^ Professor Griggs had previously, in one of his articles, expressed the opinion 

 that the material must have been extruded from fissures within the valley. See 

 article, "The Great Hot Mud Flow of the Valley of Ten Thousand Smokes," by 

 R. F. Griggs, in Ohio Journal of Science, Vol. XIX, No. 2, p. 139. 



