CRATER LAKE, ORECOX 



45 



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SECTION OF CRATER LAKE AND ITS RIM, WITH THE PROBABLE OUTLINE OF MOUNT MAZAMA 



Vertical and Horizontal Scales the same 



In the accompanying figure is given a section of Crater lake 

 and its rim, with the probable outline of Mount Mazama. Won- 

 derful as the lake, encircled b}^ cliffs, may be, it serves but to 

 conceal in part the greatest wonder — tliat is, the enormous pit 

 which is half filled by the lake. The pit or caldera, as it is called 

 by some geologists, is 4,000 feet deep. It extends from the top 

 of the rim half-way down to the sea-level, and nearly a square 

 mile of its bottom is below the level of Upper Klamath lake at 

 the eastern foot of the range. The volume of the pit is nearly a 

 dozen cubic miles, and if we add the volume of the lost Mount 

 Mazama, that amount would be increased by at least one-half 

 How was it possible to remove so large a mass and in the process 

 develop so great a pit? 



The pit is completely inclosed, so that it cannot be regarded 

 as an effect of erosion. The volcanic origin of everything about 

 the lake would suggest in a general way that this great revolu- 

 tion must have been wrought by volcanism, either blown out by 

 a great volcanic explosion or swallowed up by an eijualh' great 

 engulfment. It is well known that pits have been produced by 

 volcanic explosions, and some of them are occupied by lakes of 

 the kind usually called crater lakes. Pits produced in this way, 

 however, are, with rare excei)tions, surrounded by rims composed 

 of the fragmental material l)l()wn from the pit. 



At first sight the rim about Crater lake suggests that the pit 

 was ))roduced by an exjjlosion, and the occurrence of much 

 l)umice in that region lends support to this i)reliminary view ; 

 but on careful examination we find, as already stated, that the 

 rim is not made up of fragments blown from the pit, but of layers 

 of solid lava interbedded with those of volcanic conglomerate 

 erui)ted from Mount Mazama before the i)it originated. The 



