152 J. W. Shipley — Volcanic Emanations in Alaska. 



water as such does not occur. That the disintegration 

 of the ash in the mud flow was modified at considerable 

 depth was evidenced by a cave-in exposing a subterra- 

 nean, horizontal tunnel, twelve feet in diameter and sev- 

 enty-five feet below the surface. The walls were 

 composed of the characteristic mud flow material baked 

 a deep brick red, apparently unattacked and containing 

 no incrustants. Tunnels closer to the surface were 

 heavily incrusted due to the cooling down of the vapors 

 and sublimates and the possibility of salt formation and 

 transportation in the presence of water. 



Stream erosion across several active areas exposed 

 cross sections of some of these tunnels, giving an excel- 

 lent opportunity for studying the disintegration and depo- 

 sition of material in the surface layers of the mud flow. 

 Directly above the tunnel the ash was almost completely 

 disintegrated and replaced by a deposit of Si0 2 while 

 laterally the decomposition fell off and the ash was im- 

 pregnated with deposits of oxides, sulphates, phosphates 

 and chlorides together with amorphous Si0 2 . The af- 

 fected area extended from the tunnel fan-wise to the 

 surface with the greatest accumulation of salts near the 

 surface. 



Conclusion. — It is quite impossible to differentiate 

 the primary and secondary volcanic compounds in this 

 region. The majority of the incrustants examined were 

 secondary products arising from the decomposition of the 

 ash by the volcanic gases, but, on the other hand, the 

 great volume of escaping vapors has a magmatic origin. 

 Gautier 12 and other investigators have shown that most 

 of the gaseous products and sublimates observed in vol- 

 canic emanations can arise from the interaction of water, 

 carbon dioxide, and the solid constituents of the lava. 

 In the Valley of 10,000 Smokes, water vapor is the major 

 constituent of the emanations. Its origin is debatable, 

 but according to Gautier, one cubic kilometer of granite 

 can provide 30,700,000 metric tons of water from its water 

 of combination and oxidizible hydrogen. Consequently, 

 should a portion of the earth's crystallized crust come in 

 contact with the heated magma, sufficient water could be 

 freed to give rise to the phenomena observed in the Valley 

 of 10,000 Smokes. 



Much of the surface drainage enters the porous mud 

 flow and adds its quota to the saturation of the ash. Sur- 



12 Compt. Kend., vol. 142, p. 1465, 1906. 



