A vent or vents fed by the Devils Backbone dike system emitted voluminous outpourings of andesite of Devils Backbone and created an extensive lava flow on the northwestern flank of Mount Mazama between 50,000 and 40,000 years ago. As seen in the caldera wall, the Devils Backbone dike cuts numerous older lava flows.

Mount Mazama’s most violent eruption occurred about 7,700 years ago. A column of hot gas and volcanic rock was ejected high into the air. This magma fell to the earth as fragments of frothy white pumice and volcanic ash. Layers of ash from this eruption may still be found in the soil as far away as Alberta, Canada, more than 1,000 miles away. Explosions on the northeast side of the mountain produced fast-moving flows of hot ash. In all, 12 cubic miles (50 cubic kilometers) of material poured out of the volcano, draining the magma chamber beneath it. As the underlying support for the mountain was lost, the walls of the volcano began to collapse inward. The top of a mountain that was built over hundreds of thousands of years probably “disappeared” in a few days.

Credits and Sources:

"Crater Lake National Park Geologic Resources Inventory Report," National Park Service, http://www.nps.gov/crla/learn/nature/loader.cfm?csModule=security/getfile&pageid=666498 (accessed November 4, 2015).

"Geology," National Park Service, http://www.nps.gov/crla/planyourvisit/upload/Geology.pdf (accessed November 4, 2015).