12762 – 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: 12762

Reporting Year: 1995

Permit Number: CRLA1995AOLM

Date Received: Jan 01, 1998

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

Park-assigned Study Id. # CRLA1995AOLM

Permit Expiration Date: Jan 01, 1998

Permit Start Date: Jan 01, 1998

Study Starting Date: Jan 01, 1995

Study Ending Date: Jan 01, 1995

Study Status: Completed

Activity Type: Other

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:  Work continues on preparation of the 1:24,000 scale geologic map for publication. Drafts of all eleven geologic panoramas of the caldera walls have been completed and are being scanned. These will be published in color along with the geologic map. Two weeks were spent in the field checking the geology of the caldera walls and collecting additional rock samples to verify correlations and identification of map units. In cooperation with USGS colleagues at the Cascades Volcano Observatory, work was begun on a volcano hazards assessment of the Crater Lake area. A paper on primitiv lavas in five Cascade volcanic centers, one of which is Crater Lake, was submitted for publication. ;Field work in 1995 clarified many stratigraphic relationships amoung the lavas from different volcanic centers that make up Mount Mazama. Lava flows and pyrroclastic rocks from five to ten sources can be found in any one caldera wall section. These can be correlated around the caldera and matched with exposures on the flanks of Mount Mazama. Compilation of our K-Ar 40Ar/39Ar dates of lava flows that are offset along the major north-south normal fault that goes through Annie springs indicate a long-term average vertical displacement rate along this fault of 0.3mm/yr, down-to-the-east, for the last 300,000 years. This fault is part of the same system that bounds the west side of the Klamath graben (basin) and connects with epicental area of the September, 1993, “Klamath Falls” magnitude 6 earthquakes.

For this study, were one or more specimens collected and removed from the park but not destroyed during analyses?

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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