110 



The Ohio Journal of Science [Vol. XIX, No. 2, 



Photograph by R. F. Griggs 

 A FILLED CRATER IN THE MUD FLOW. 



The crater was formed in the mud flow by explosive action originating below the 

 base of the section, which here rests on undisturbed sandstone strata exposed 

 by the stream in the foreground. This crater stood open during the explosion 

 of Katmai, whose three-layered ash, marked K, may be plainly seen on the 

 top of the original mud surface. Later there came a secondary flow of mud 

 which filled up the crater and piled up about ten feet above the surface of the 

 primary flow. The fill did not. however, choke off the fumarole which for 

 some time maintained an open vent to the surface, shown in the photograph 

 by a faint vertical streak rising from the bottom of the crater. 



