14:2 J. W. Shipley — Volcanic Emanations in Alaska. 



eventually baked. An examination of the baked mud 

 showed it to be made up of angular pumice, tuff and 

 volcanic ash having a specific gravity almost identical 

 with that of building brick. The contracting, hardening 

 mass split and cracked according to the strains and 

 stresses set up by the irregularities of the valley floor 

 beneath. The volcanic gases force their way upward 

 through this superincumbent detrital material, using the 

 existing cracks and fissures and dissolving out new chan- 

 nels where these were not available. The area covered 

 by the mud flow is about fifty square miles and, by a 

 strange coincidence, the limits of the mud flow are ap- 

 proximately the limits of the volcanic activity. 



The distribution and superficial characteristics of the 

 volcanic vents over this area have been excellently de- 

 scribed by Griggs. 4 The great volume of gases pour 

 out from large well-defined vents, but in addition to these, 

 the volcanic emanations exude from the surface of the 

 mud flow over large areas not possessing any visible 

 orifices whatsoever. The gases issue under considerable 

 pressure at temperatures varying from atmospheric to 

 well above 400 °C. Unfortunately, the boiling point of 

 mercury was the limit of our thermometry, but in 1918 

 Sayre and Hagelbarger with a thermo-electric pyrometer 

 observed temperatures of 450° C. Our own observations 

 indicated much higher temperatures than our thermo- 

 meters would register. 



The nature of the incrustations in the neighborhood of 

 a vent was largely determined by the temperature of the 

 issuing gases. Where the temperature was high the 

 incrustations were anhydrous and baked and contained 

 none of the more volatile sublimates or hydrated salts. 

 Deposits of sulphur or orpiment were not found adjacent 

 to a very hot vent and the deposition of ammonium chlor- 

 ide was in the throats of orifices little hotter than 100° C. 



The Nature of the Gases. — The major part of the issu- 

 ing gases consisted of water vapor. Many fumaroles 

 emitted little else, but on the other hand, a few were al- 

 most anhydrous, scarcely any moisture condensing from 

 samples drawn off. The latter were invariably strongly 

 acid and in one particular contained large quantities of 

 S0 3 . Hydrochloric and hydrofluoric acids were common 

 constituents of the vapors, the former being most mark- 



4 Nature, vol. 101, p. 497, Aug. 22, 1918. 



5 National Geog. Magazine, vol. 33, Feb. 1918. 



