THE K AT MAI REGION, ALASKA 



591 



short interval of time in which the rapidly cooling mass possessed 

 a rigid crust and a plastic interior. The point to be noted is that 

 the magma, rising into the crater from the depths below, did not 

 immediately pufi up into pumiceous masses, but accumulated, at 

 times certainly, in pools of non-vesicular lava. The surprising 

 thing is that this condition held in spite of the relief of pressure. 

 On the other hand, we have evidence that under certain conditions 

 very great pressure did not avail to hold the gases in solution. 

 This is furnished by the lava that was later extruded and now 

 forms the dome. In spite of the enormous pressure to which this 



Fig. 15. — Mount Katmai, from the Island Camp. The crater pit extends across 

 nearly the whole space between the two summits. Photograph by R. F. Griggs, 1917. 



was subjected during extrusion, the contained gases came out of 

 Solution and filled the glass with minute vesicles. The explanation 

 of such phenomena as these will be undertaken later. 



MOUNT KATMAI AND ITS EJECTA 



Let us consider now some of the features of Mount Katmai, 

 and first the form of the crater as it appears since the eruption. 

 The present appearance of Katmai is shown in Figure 15. Before 

 the eruption the height, as shown by the Coast and Geodetric 

 Survey chart, was 7,500 feet. The top of the mountain has now 

 disappeared and an enormous crater abyss has been formed. 



