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Roger Weller, geology instructor                     

Crater Lake, Oregon
Jennifer Jacobs
Physical Geology
Fall 2005

                                                    Crater Lake, Oregon

Image courtesy of USGS/Cascades Volcano Observatory


World’s Best Known Caldera


Mount Mazama, a stratovolcano,  erupted 6,850 years ago causing a collapse of the mountain which in turn created what is know today as Crater Lake located in Oregon is a caldera and is also the deepest lake in North America.  This caldera is approximately 6 miles wide.  The catastrophic pyroclastic eruption of Mount Mazama released about 12 miles cube of magma on the surface.


The eruption of Mount Mazama deposited a large amount of volcanic ash that covered six states and a good portion of Canada stretching from the Washington state line to Montana along the Canadian border.  Along with volcanic ash deposits, there was also a deposit of pumice stones over a wide area as well


The cinder cone located in Crater Lake named “Wizard Island”  is approximately 760 feet above the lake on the west side.  Wizard Island also contains a crater left by a more recent eruption that took place 4 to 500 years ago.  This eruption left a depression that measure 300 feet across and 90 feet in depth.


Lake and Wizard Island. Crater Lake National Park


As you can see, the lava from the latest eruption flowed to the west side of Wizard Island.  Developing more land coverage prior to the eruption.  In the wintertime, the depression at the top of Wizard Island fills with snow but beyond that, the surface is dry the rest of the year.  The Wizard Island volcano considered inactive has had no recent activity recorded.    
courtesy of USGS/Cascades Volcano Observatory


Crater Lake is the deepest lake in the United States at 1,932 feet deep (Double Deck p 6).  Other calderas around Crater Lake have formed over time prior to the eruption of Mount Mazama and the birth of Wizard Island.  All of these volcanos have produced a variety of rocks and minerals that surround Crater Lake.  Here is a diagram of the lay out of Crater Lake and sibling calderas.

Erosional remnants of a pyroclastic flow


Crater walls and lake. Crater Lake National Park

Walls of Crater Lake.


Map, Geologic Map of Crater Lake Caldera Floor

Image courtesy of USGS/Cascades Volcano Observatory