21365 – Conduit processes of the Cleetwood eruption, inferred from textural, petrologic, and water content analyses

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

Conduit processes of the Cleetwood eruption, inferred from textural, petrologic, and water content analyses


Report Number: 21365

Reporting Year: 2001

Permit Number: CRLA-2001-SCI-0009

Date Received: Feb 28, 2002

Principal Investigator: Katherine Wearn, Department of Geol. Sciences, University of Oregon, Eugene, OR

Additional investigator(s): Dr. Katharine V. Cashman  

Park-assigned Study Id. # CRLA-01033

Permit Expiration Date: Dec 31, 2001

Permit Start Date: Sep 10, 2001

Study Starting Date: Sep 13, 2001

Study Ending Date: Aug 10, 2002

Study Status: Continuing

Activity Type: Research

Subject/Discipline: Geothermal / Volcanology

Objectives: The main objective of this project is to complete a detailed petrologic study of the pyroclastic obsidian produced by Mt. Mazama’s pre-climactic Cleetwood eruption. Water content analyses of the obsidian clasts will be used to infer information about how the physical conditions, and in particular the fragmentation level, within the conduit evolved over the course of the eruption, as well as to develop a model of the eruption’s transition from explosive to effusive eruptive style. We will compare the data obtained from the Cleetwood pyroclastic deposit with those from other pyroclastic deposits associated with similar explosive-effusive eruptions, notably the Rock Mesa eruption that occurred southwest of South Sister and the eruption sequence that culminated in the emplacement of the Mono craters domes in California. Analyses and comparisons of these deposits should help determine what role obsidian plays in explosive-effusive transitional eruptions and will cultivate a better general understanding of the physical processes that take place in volcanic conduits.

Findings and Status: All sample collection for this project has been completed and data analysis is ongoing. Grainsize distributions have been completed, and componentry analysis of the Cleetwood samples has revealed that pyroclastic obsidian is present in significant but varying proportions throughout the deposit. Preliminary water content analyses suggest that the fragmentation level migrated over the course of the eruption, and that perhaps this migration was responsible for the eruption’s explosive-effusive transition. Further FTIR analysis should help quantify the evolution of physical conditions in the conduit over the course of the eruption, and it is anticipated that comparison with Rock Mesa and Mono craters deposits will show that pyroclastic obsidian is a more common product of explosive-effusive transitional eruptions than has previously been believed, and that data collected from these clasts can be useful in assessing some of the mechanisms involved in the eruptive process.

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

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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