Graduation Year

2008

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Geology

Major Professor

Charles B. Connor, Ph.D.

Committee Member

Onno Bokhove, Ph.D.

Committee Member

Costanza Bonadonna, Ph.D.

Committee Member

Sarah E. Kruse, Ph.D.

Committee Member

Paul H. Wetmore, Ph.D.

Keywords

Eruption triggering, eruption dynamics, magma ascent mechanisms, volcano-tectonic interaction, static stress changes, Rayleigh-Taylor instability in magmas, volcano conduit geometry and structure, San Rafael subvolcanic field, Cerro Negro Volcano, wallrock rheology

Abstract

Volcanic activity, and the resultant deposits and structures at the Earth's surface, are the outcome of the inner workings of underground magmatic plumbing systems. These systems, essentially, consist of magma reservoirs which supply magma to the surface through volcanic conduits feeding volcanic eruptions. The mechanics and structure of plumbing systems remain largely unknown due to the obvious challenges involved in inferring volcanic processes occurring underground from observations at the surface. Nevertheless, volcanologists are beginning to gain a deeper understanding of the workings and architecture of magmatic plumbing systems from geophysical observations on active volcanoes, as well as from geological studies of the erosional remnants of ancient volcanic systems.

In this work, I explore the relationship between the structure and mechanics of shallow plumbing systems and the volcanic eruptions these systems produce. I attempt to contribute to the understanding of this complex relationship by linking geological and geophysical observations of an eroded basaltic subvolcanic system, and the eruptive and tectonic activity of an active volcano, with mathematical models of magma ascent and stress transfer.

The remarkable exposures of the Carmel outcrop intrusions, near the San Rafael swell, southeast Utah, U. S. A., allow detailed geological and geophysical observations of the roots of volcanic conduits that emerge from a subhorizontal magma feeder reservoir. These observations reveal a new mechanism for magma ascent and eruption triggering through gravitational instabilities created from an underlying feeding sill, and shed light on the mechanics of sill emplacement. Geophysical and geological observations of the 1999 and xii 1992 eruptions of the Cerro Negro volcano, Nicaragua, are used to explore the coupling between changes in the stress field and the triggering of volcanic eruptions, and magma ascent through the shallow crust. Modeling results of stress transfer and conduit flow highlight the importance of the surrounding stress field and geometry of the volcanic conduits that comprise shallow plumbing systems.

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