In previous issues of these notes evidence and theories as to the formation of the caldera in which Crater Lake lies were discussed. A few facts concerning the lake itself may be of interest.

Since the Rim of Crater Lake is the base of the original Mt. Mazama, drainage from the lake and into the lake is represented throughout its entire circumference by the very edge of these cliffs alone. The walls are exceedingly sheer. At no point is there a stream of even small size flowing over the edge, into the caldera. The water in the lake therefore is the rain and snow which falls upon it directly or upon the very narrow area of the cliffs. Hence it may be considered as not only very pure water, but actually distilled water. Any mineral content would be negligible because of the small drainage area, and because of the character of the rock composing the walls. Many springs, some of considerable size, issue from the walls, and would add to the mineral content, but this also would be proportionately insignificant considering the quantity of water present, since the lake is nearly two thousand feet deep, with an area of over twenty square miles.

The water level changes about four feet throughout the year, being highest during maximum melting of snow, after the winter season and lowest in September or early October. Precipitation is estimated to average over 60 inches per year. Great amounts of snow are blown over the edge of the rim. Then too, the numerous springs add to the accretion. Evaporation is estimated to be about forty inched per year. Calculations on the rate of lowering and rate of evaporation indicate a more rapid lowering than could be accounted for by this agency alone. Since there is no surface outlet the surplus probably escapes through the porous rocks of the walls reappearing as springs which are numerous on the southeast base of Mt. Mazama.