xviii, 179 p. : ill. (some col.). Includes 3 video files. / Mafic arc volcanoes have eruption styles that range from explosive to effusive. In a broad sense, eruption style is controlled by the rate of magma supply to the vent. In this dissertation I examine relationships between eruption rate and style in two separate studies: (1) an investigation of ongoing activity at NW Rota-1, a submarine volcano in the Mariana arc, and (2) a morphologic study of the Collier Cone lava flow field in the Central Oregon Cascades.
The eruptions of NW Rota-1 range from effusive to moderately explosive; eruptions are effusive when mass eruption rate (MER) is low and explosive when MER increases. The explosivity of submarine eruptions is suppressed by seawater because of increased hydrostatic pressure, rapid cooling, and the high viscosity of water relative to air (which limits expansion). The combination of seawater and relatively low MERs limit pyroclast deposition to within meters to tens of meters of the vent. In fact, many pyroclasts fall back into the vent and are recycled. Evidence for recycling includes microcrystalline inclusions within erupted pyroclasts and elevated Cl and Na concentrations in matrix glass. Enrichment of Cl and Na suggests that seawater assimilation provides a geochemical signature of recycling. Recycling is limited to low MER explosive eruptions and is not observed in either effusive lava or deposits from high MER explosions.
Direct observations of eruptions allow measurements of eruption rate. However, it is more challenging to estimate MERs of eruptions that were not observed. To address this problem, I develop and test methods of constraining the eruption rate (and duration) of the c. 1600 year old Collier Cone lava flow using the flow morphology. To quantify flow morphology I combine field observations with GIS analysis of Lidar-derived digital topography. Channel dimensions constrain emplacement rates; dominant wavelengths and amplitudes of surface folds constrain spatial and temporal changes in flow rheology.
Three videos of eruption activity accompany this dissertation as supplemental files.
This dissertation includes both previously published and unpublished co-authored material. / Committee in charge: Dr. Katharine V. Cashman, Chair;
Dr. Joshua J. Roering, Member;
Dr. Paul J. Wallace, Member;
Dr. Patricia F. McDowell, Outside Member;
Dr. William W. Chadwick, Outside Member
| Identifer | oai:union.ndltd.org:uoregon.edu/oai:scholarsbank.uoregon.edu:1794/11969 |
| Date | 09 1900 |
| Creators | Deardorff, Nicholas D., 1980- |
| Publisher | University of Oregon |
| Source Sets | University of Oregon |
| Language | en_US |
| Detected Language | English |
| Type | Thesis |
| Rights | rights_reserved |
| Relation | University of Oregon theses, Dept. of Geological Sciences, Ph. D., 2011; |
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