Dec., 1918] The Great Hot Mud Flow 131 



blowout of Mt. Katmai, made it more difficult than ever to 

 find the source of the material. The high temperature which 

 characterized the moving mud definitely put it into a different 

 class from the Katmai Mud Flow. And the freshness of the 

 plant remains and other features combined to fix its date as 

 immediately prior to the explosion of Katmai. 



MUD FLOW VERY DIFFERENT FROM A LAVA FLOW. 



One way out of these difficulties at once suggested itself. 

 If we could consider this formation a lava flow rather than a 

 mud flow, its explanation would be easy, for a lava flow of such 

 dimensions would be' nothing remarkable. But lava comes from 

 a mass of molten magma which solidifies into crystalline rock. 

 By no stretch of the meaning of the term can this tuff be con- 

 sidered crystalline rock. It is composed of fragmental materials 

 like the ash that settles out of the air. Although compacted 

 into a firm mass, somewhat resistant to the weather, it crumbles 

 to powder between one's fingers. Though hot by human 

 standards of comparison, its temperature was far below the 

 melting point of any lava, for, although it reduced the trees 

 which it engulfed to charcoal, it did not, at least in the lower 

 Valley, set fire to the forest above the high mud mark, nor 

 even consume the trees that were not completely covered up. 

 On the contrary, the projecting parts of the burned trees 

 were sound and untouched by fire. Where cooled by the atmos- 

 phere, or by the underlying soil, the mud had evidently lost 

 its heat before charring was complete, for the stumps were not 

 burned clear to the ground and good sized branches were 

 charred through only when buried a foot beneath its surface. 

 This indicates that the charring was a gradual process rather 

 than any sudden combustion, such as breaks forth when a 

 lava flow pours through a forest. (See page 133). 



ATTEMPTS TO EXPLAIN IT AS A MUD FLOW OF THE 

 USUAL TYPE. 



When it thus became evident that our flow of hot mud 

 could not be considered a lava flow, the most probable explana- 

 tion seemed to lie in interpreting it as a mud flow of the con- 

 ventional kind, formed from the ejecta of some previous 

 eruption. Such a hypothesis would of course leave its temper- 

 ature unaccounted for, if indeed it were not inconsistent with 

 the observed temperature relations; but if its other features 



