378 CRATER LAKE, OREGON. 



of this phenomena seems to be that soon after the final eruption of 

 Mount Mazama, and before the thickest part of the lava effused at that 

 time had solidilied, the mountain collapsed and sank away and the yet 

 viscous portion of the stream followed down the inner slope of the 

 caldera. 



It has been suggested, but perhaps not in serious thought, that the 

 cone on Wizard Island may represent the summit of the sunken Mount 

 Mazama projecting above the water. To determine the truth of the 

 matter we must cross over to the island. Wizard Island has two por- 

 tions — an extremely rough lava field and a cinder cone. These parts 

 may be distinguished in figure 16, a view of the island from the 

 Watchman. A portion of the lava field is shown in the foreground of 

 figure 18. The lava is dark and has a much more basaltic look than 

 any seen in the main body of the rim. It has evidently been erupted 

 from the base of the cinder cone in its present position. The cinder 

 cone, too, is a perfect little volcano, with steep symmetrical slopes, 845 

 feet in height, and surmounted by a crater 80 feet deep. A portion of 

 this crater is shown in figure 17. It is so new and fresh that it 

 is scarcely forested, and shows no trace of weathering. Instead of 

 being a part of the sunken Mount Mazama, it is an entirely new vol- 

 cano built up since the subsidence by volcanic action ui)on the bottom 

 of the caldera. Were it not for the lake the whole bottom of the 

 caldera could be examined, and it is possible that other small volcanic 

 cones might be found. This suggestion is borne out by the soundings 

 of the lake, which appear to reveal two other cases, but they do not 

 rise to within 400 feet of the surface of the water. It is evident that 

 the volcanic eruptions upon the bottom of the caldera have partially 

 filled it up. Originally it may have been much more than 4,000 feet 

 deep. 



Given the caldera with water-tight walls, there is no difficulty in 

 forming Crater Lake, for in that region precipitation is greater than 

 evaporation. Observations upon precipitation and evaporation have 

 not been made at Crater Lake, but, judging from those made at nearest 

 points, the annual precipitation should be between 60 and 70 inches, 

 while the annual evaporation is between 50 and 60 inches. The aver- 

 age diameter of the lake is nearly 5 miles. Its area, including Wizard 

 Island, is about 21.30 square miles. The drainage area inclosed by the 

 rim of the lake, according to Mr. E. C. Barnard, is 27.48 square miles. 

 During the winter great masses of snow drift within the rim, and thus 

 considerably augment the normal precipitation of the lake. The lake 

 does not fill up and overflow. The surplus water must have a subterra- 

 nean outlet, ])robably toward the southeast, where the region is tra- 

 versed by extensive breaks in the rocks, and abounds in excellent 

 springs. 



The color of the lake is deep blue, excepting along the borders, where 

 it merges into various shades and tints of green. It is so transparent 



