Crater Lake's History

"All ingenuity of nature seems to have been exerted to the fullest capacity to build a grand awe-inspiring temple the likes of which the world has never seen before."

-William Gladstone Steel, 1885

        Crater Lake in southern Oregon is the site of one of the world's finest calderas.  A caldera, as defined by Easterbrook (1999), is "a large circular volcanic depression the diameter of which is many times greater than that of the included volcanic vent or vents" (524).  This particular caldera, with a maximum width at six miles and a maximum depth of 1932 feet (Uhler, 2002) is the deepest lake in the United States, and the seventh deepest lake in the world.  The elevation of the lake is 6176 feet, and the highest point on the rim is Hillman Peak, at 8151 feet (USGS, 2002).  The lake averages 66 inches of rain per annum, as well as an average of 44 feet of snow per annum (USGS, 2002).

        Up until approximately 7700 years ago, Crater Lake was the site of a giant 12000 foot stratovolcano named Mt. Mazama.  A massive explosion hollowed out the magma chamber inside of the volcano.  This hollow chamber was not able to support the enormous weight of the volcano, and thus, the volcano collapsed.  Further lava flows effectively sealed the bottom of the caldera.  The impermeable rock allowed rainwater and snowmelt brought the lake to its current level.

                                                                                                                                                              
    
                                                                                                                                                                                            An artists rendition of the Mt. Mazama eruption, courtesy of the USGS.

        There is no fluvial output to Crater Lake.  That is, there are no creeks or streams to carry water away.  How is it then, that with the massive snowmelt that enters the lake each year, that the lake remains relatively constant?  The water levels are regulated in two ways: evaporation, and sub-surface seepage.  These two factors are in relative equilibrium with the input of rain and snow, hence the level of the lake has very minimal variation from year to year.         

How does the lake get its strikingly blue color?

        A common question that visitors ask is "why is the lake so blue?"  According to Warfield et. al (1996), there are several factors.  First of all, the lake has low levels of dissolved minerals, giving it no true color.  Furthermore, its low concentration of suspended particles and organic matter give it the deep transparency.  When light enters the water, some is absorbed, and some is scattered.  Colors with long wavelengths (red, yellow, and orange) are absorbed within a couple meters of the surface.  Greens are absorbed further down, but blues, which have short wavelengths, can penetrate to 120 feet.  The water molecules can then scatter the blues from a great depth.  This gives the lake its intense blue color.

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Reference: Easterbrook, D.J.  (1999).  Surface Processes and Landforms, 2nd ed.  Prentice Hall, New Jersey.