CAUSES OP VOLCANIC ACTIVITY — DAY 267 



appears adequate to account both for the initiation and the progress 

 of explosive volcanic activity at Lassen Peak during the p?riod of 

 1914 to 1917. It also indicates the source of the vast amount of water 

 vapor which is given off in the course of a long series of explosive 

 eruptions. 



In this discussion of the phenomena at Lassen Peak we appear to 

 have reached an answer to one of the two questions posed earlier m 

 this address, namely, the point of probable origin of the gases which 

 participate in volcanic activity. They are in solution in the crys- 

 tallizing magma and their release takes place under appropriate con- 

 ditions of temperature and pressure when this magma crystallizes to 

 rock. Chief among these volatile ingredients is undoubtedly water 

 in most if not in all cases. If water be substantially the only ingre- 

 dient, as at Lassen Peak, then the volcanic outbreak will consist in 

 discharges of dust-laden steam, and such solid material as may be 

 carried out by attrition. If temperatures are higher and the vola- 

 tile ingredients include chemically active gases such as chlorine, 

 fluorine, sulphur, hydrogen, and the like, then an accelerated type of 

 development may be expected, due to the higher temperatures result- 

 ing from the combination of these gases when oxidized either 

 through reactions within the magna or with oxygen from the air. 

 Under such conditions the magma may be forced out in liquid con- 

 dition (lava flow) and may crystallize in the open air. After observ- 

 ing the persistance of the open lava lake and noting, as Professor 

 Jaggar has been able to do by measurement, that the temperature at 

 the surface is higher tlian it is immediately beneath the surface, it 

 again requires but little of the imagination to enable one to under- 

 stand how such gas reactions may provide the necessary energy to 

 maintain the lake in fluid condition. The origin of the gases here, as 

 in the case of Lassen Peak, must be sought in crystallizing magma at 

 different depths where differences of temperature and pressure must 

 be responsible for very considerable inhomogeneities (differences of 

 concentration) in the gases from different local sources. 



The Kilauea crater is not appropriately pictured as an ordinary 

 boiling flask with a long narrow neck. It is very doubtful if we 

 have any ground for such a picture. At any rate during the past 

 summer (1924) when the lava lake had been drained away through 

 subterranean channels and the gases were escaping explosively from 

 the empty basin, the crater was enlarged by the explosions to about 

 3,500 feet in diameter and 1,500 feet in depth. The volcanic throat 

 was thus laid open to a depth more than twice as great as on any pre- 

 vious occasion since it came under the observation of white men, and 

 a rare and precious opportunity was offered to see what manner of 

 material occupied the next 800 feet immediately under the lava lake, 



