592 CLARENCE N. FENNER 



Measurements made by Mr. C. F. Maynard, topographer of the 

 1 91 7 expedition, give the dimensions of this pit as 2 to 2^ miles 

 in diameter and 2,000 to 3,700 feet in depth. About one-haK of 

 the area at the bottom is covered by a sheet of water of a pecuKar, 

 milky, turquoise-blue or green color, and from near the center of 

 this lake rises a crescentic island. To one standing on the edge 

 of the pit the cliffs appear almost vertical, but their inclination is 

 probably not more than 60° to 70° on the average. They seem to 

 be made up entirely of a succession of lava flows. On the western 

 side of the rim, for about one-third of the circumference, an ice 

 wall appears — a survival of beheaded glaciers, and the depression 

 in the southern side of the rim is floored with bowlder deposits 

 of morainal origin. The bottom of the crater, where not covered 

 by the lake, appears from above approximately flat. At the foot 

 of the cliffs are talus deposits, which appear of rather insignificant 

 proportions. At present the activity is very slight. Steam rises 

 slowly from a number of fissures and clefts near the bottom, and 

 the water of the lake is evidently warm, but on August 10 snow 

 was lying in many places on the crater floor. 



The crater of Katmai is a most wonderful and impressive sight, 

 and photographs give but a very inadequate idea of its tremendous 

 proportions (Fig. 16). 



A matter of great interest is that of the mechanism by which 

 this huge pit was formed, for this is intimately related to the 

 question of the volcanic processes attending eruptions. Professor 

 Griggs had recognized the importance of solving this problem and 

 had called particular attention to it before our departure for the 

 region. One's first view would naturally be that the material 

 was blown out bodily in the eruption, but there is good evidence 

 that this is not the whole explanation. A remarkable characteristic 

 of the ejected material is the small dimensions of the fragments. 

 Even on the upper slopes of the mountain there are not many 

 pieces above the diameter of a few inches, and a great proportion 

 of them are much finer. Moreover, almost all the larger pieces 

 are of pumice, and the fragments of older rock have a general 

 maximum size even less than the figures given. Also the propor- 

 tion of these older andesites is rather small, not nearly sufficient 



