Dec, 1918] The Great Hot Mud Flow 135 



great expanse of country. The mud that gave rise to the 

 relatively insignificant Katmai Mud Flow is recognizable as a 

 distinct stratum on top of the rest of the ashfall over all "of the 

 mainland country as far away as the seashore. The mass of 

 the mud in the Great Mud Flow is so many times greater 

 than this that traces of the antecedant bed from which it 

 came would certainly have been found somewhere, if it was 

 produced in a manner at all resembling the mud of the Katmai 

 Flow. 



The only geologist who ever visited the district, before the 

 eruption, was J. E. Spurr, who in 1898 crossed Katmai Pass, 

 traversing both Katmai Valley and what is now the Valley of 

 Ten Thousand Smokes, then an ordinary grass covered valley. 

 His account makes no mention of any deposit of fragmental 

 volcanic material of any sort. vSince the discovery of the mud 

 flow I have had the opportunity of talking the matter over with 

 Mr. Spurr, who stated, in the most positive terms, that there 

 was no such deposit along his trail. And, as will be showm 

 below, the distribution and slopes of the mud flow are such that 

 part of it must have originated in Katmai Pass, which he 

 crossed. But let us assume, for the sake of the argument, that 

 a deposit of the mass and character requisite for the formation 

 of the mud flow was actually present before the eruption, even 

 though no trace of it has been found by any of the parties that 

 have explored the district. 



NO DR-\INAGE AREA FROM WHICH IT COULD HAVE BEEN 



CONCENTRATED. 



Such an assumption immediately raises one of the difficulties 

 that confronted us in our first efforts to find a source for the mud 

 of the Valley. The area of the broad Valley is so great, in 

 proportion to the steep slopes of the surrounding mountains, 

 that there is no tributary drainage area around its upper end 

 large enough to have served as a collecting ground from which 

 the mud could have come. The mud flow thus covers almost 

 half of the drainage area from which it could have come. Its 

 area is 53 square miles, while that of the whole basin is only 

 110 square miles. If these mountain sides supplied the material 

 that now covers the Valley, they must have been everywhere 

 covered to a depth approximately equivalent to the present 

 thickness of the tuff of the Valley, i. e., at least 50 feet. This is 



