12846 – Volcanic Evolution of the Crater Lake Region

Investigator’s Annual Reports (IAR’s) for Crater Lake National Park

Volcanic Evolution of the Crater Lake Region


Report Number: 12846

Reporting Year: 1999

Permit Number: CRLA199902-004

Date Received: Jan 01, 2000

Principal Investigator: Charles R. Bacon, U.S. Geological Survey, U.S.G.S., Menlo park, CA

Additional investigator(s): Duane Champion

Park-assigned Study Id. # CRLA199902-004

Permit Expiration Date: Jan 01, 2005

Permit Start Date: Jan 01, 2000

Study Starting Date: Jan 01, 1979

Study Ending Date: Jan 01, 2005

Study Status: Completed

Activity Type: Research

Subject/Discipline: Geology / General

Objectives: To document the growth and evolution of Mount Mazama, the volcanic complex in which Crater Lake caldera lies, in order to define processes that led to an accumulation of a large volume of silicic magma in the upper crust. Secondary goals are to further knowledge of catastrophic eruptions, such as the one that resulted in the collapse of the caldera.

Findings and Status:  The 1:24,000 scale geologic map of Mount Mazama and Crater Lake caldera is being prepared for publication. Digital files of the geologic map and all eleven geologic panoramas of the caldera walls have been completed in ArcInfo. Geologic unit descriptions will be completed in 2000. These will be published in color and the map also will be released in digital form. A paper on the slip rate on the West Klamath Lake fault zone near Crater Lake was published in the journal, “Geology”. Dr. Charles Mandeville, American Museum of Natural History, continued working on on sulfur isotope determinations in volcanic rocks from Crater Lake in order to elucidate processes of gas loss from Mount Mazama prior to and during volcanic eruptions. Dr. Marvin Lanphere, USGS, and co-workers measured several new K-Ar and Ar-Ar ages of volcanic rocks from Carter Lake. These data will be published in a companion paper to the geologic map. A significant new finding resulted from ion microprobe U-Pb and U-Th dating of zircon from granitic blocks ejected in the caldera-forming eruption. These results, presented at the Fall Meeting of the American Geophysical Union and submitted for publication in Geology, indicate that the shallow pluton from which the blocks were derived was intruded beneath Mount Mazama approximately 110,000 years ago. Field work in 1999 consisted of sampling lava from Scoria Cone for paleomagnetic determinations and providing advice to Dr. Mandeville on sample sites for his study.

For this study, were one or more specimens collected and removed from the park but not destroyed during analyses? No

Funding provided this reporting year by NPS: 0

Funding provided this reporting year by other sources: 0

Full name of college or university:  n/a

Annual funding provided by NPS to university or college this reporting year: 0


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