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==Geology== {{Details|Mount Mazama}} {{stack| [[File:Crater Lake ISS (rotated and cropped).jpg|thumb|Satellite view of Crater Lake.]] [[File:Relief map of Crater Lake area.jpg|thumb|Relief map of Crater Lake area.]] }} Volcanic activity in this area is fed by [[subduction]] off the coast of Oregon as the [[Juan de Fuca Plate]] slips below the [[North American Plate]] (see [[plate tectonics]]). Heat and compression generated by this movement has created a [[mountain chain]] topped by a series of volcanoes, which together are called the [[Cascade Range]]. The large volcanoes in the range are called the High Cascades. The range has many other volcanoes, however, most of which are much smaller.{{fact|date=April 2025}} About 400,000 years ago (400 kya), [[Mount Mazama]] began its existence in much the same way as the other mountains of the High Cascades, as overlapping [[shield volcano]]es. Over time, alternating layers of [[lava]] flows and [[pyroclastic flow]]s built Mazama's overlapping cones until it reached about {{convert|11000|ft}} in height.{{fact|date=April 2025}} As the young [[stratovolcano]] grew, many smaller volcanoes and volcanic vents were built in the area of the park and just outside what are now the park's borders. Chief among these were [[volcanic cone#Cinder cone|cinder cones]]. Although the early examples are gone, since cinder cones [[Erosion|erode]] easily, the park features at least 13 much younger cinder cones, as well as at least another 11 or so outside its borders, that still retain their distinctive cinder cone appearance. Debate has continued as to whether these minor volcanoes and vents were parasitic to Mazama's [[magma chamber]] and system or whether they were related to background Oregon Cascade volcanism.{{fact|date=April 2025}} After a period of dormancy, Mazama became active again. Then, around 5700 BCE, Mazama collapsed into itself during a tremendous [[volcanic eruption]], losing {{convert|2500|to|3500|ft}} in height. The eruption formed a large [[caldera]] that, depending on the prevailing climate, was filled in about 740 years, forming [[Crater Lake]].<ref> {{cite journal | author = Manuel Nathenson |author2=Charles R. Bacon |author3=David W. Ramsey | title = Subaqueous geology and a filling model for Crater Lake, Oregon | journal = [[Hydrobiologia]] | volume = 574 | pages = 13β27 | year = 2007 |issue=1 | doi = 10.1007/s10750-006-0343-5 |bibcode=2007HyBio.574...13N |s2cid=39578681 |url=https://zenodo.org/record/1232804 }}</ref> The eruptive period that decapitated Mazama also laid waste to much of the greater Crater Lake area and deposited [[volcanic ash|ash]] as far east as the northwest corner of what is now [[Yellowstone National Park]], as far south as central [[Nevada]], and as far north as southern [[British Columbia]]. It produced more than 150 times as much ash as the May 18, [[1980 eruption of Mount St. Helens]].{{fact|date=April 2025}} This ash has since developed a [[soil]] type called [[andisol]]. Soils in Crater Lake National Park are brown, dark brown or dark grayish-brown sandy loams or loamy sands which have plentiful cobbles, gravel, and stones. They are slightly to moderately acidic and their drainage is somewhat excessive.{{fact|date=April 2025}}
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