Graduation Year

2021

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Geology

Major Professor

Timothy H. Dixon, Ph.D.

Committee Member

Batuhan Osmanoglu, Ph.D.

Committee Member

Kruse Sarah, Ph.D.

Committee Member

Ruiliang Pu, Ph.D.

Committee Member

Mark Rains, Ph.D.

Keywords

Digital Elevation Models, Flow Dynamics, Mass Flow Deposits, Stratigraphy and Sedimentology, Synthetic Aperture Radar, Topographic Changes

Abstract

Although one of the most spectacular phenomena of active volcanoes, Pyroclastic density currents, or PDCs, are considered the most dangerous volcanic hazards. PDCs are avalanches of hot volcanic gases, ash, and larger volcanic fragments that travel at incredible speed down the flank of a volcano. High dynamic pressures, high temperatures, and high velocities are the primary dangers associated with PDCs and lead to near-complete destruction and death.

I use a multi-disciplinary approach to study the deposits left behind by PDCs, in order to understand their dynamics, their interactions with the receiving landscape, and their final distribution, starting on the ground and going up to space. The study cases of this research are two PDC events that occurred in 2015 at Volcán de Colima in Mexico, and at Volcán Calbuco in Chile. The main goals of this dissertation are (1) to add to the collection of field deposit studies of PDCs, (2) to quantify the control of the topography on the path and distribution of PDC deposits, (3) to demonstrate the advantages of remote sensing techniques for both long-term hazard assessment and short-term crisis management of PDCs, as well as lahars which are frequent secondary hazards.

The first part of this work focuses on field-based observations and a detailed analysis of these PDC deposits. Although the PDC-forming eruptions at Colima and Calbuco were different (i.e., dome-collapse vs. column-collapse), the common conclusion drawn from both sets of PDCs is that they were primarily controlled by topography. Mainly, the morphology of the valleys in which the PDC deposited, which includes the cross-sectional area, the volumetric capacity, the sinuosity, and the slope of the channels, had significant impacts on the final footprint of the PDC deposits.

These field-based results are used as validation for the second part of this research, which focuses on spaceborne remote sensing data. A combination of optical, synthetic aperture radar, or SAR, and thermal satellite sensors is successfully used to track PDC and lahar deposits from space, thus opening an avenue for application to post-eruption crisis management efforts. Optical data at medium and very high spatial resolution (30 to 1 meter) are also used to build digital elevation models or DEMs. The DEMs are used (1) to measure channel morphology parameters, (2) to retrieve volumes of PDC deposits and other erupted products such as lava dome and lava flows at Colima, and (3) in a time-series to track topographic changes caused by eruption at these two volcanoes.

The techniques developed and presented in this dissertation show reproducibility across two different types of PDC events, and therefore suggest applicability to other, both past and future PDC-forming eruptions. For instance, tracking topographic changes at active volcanoes could help update hazard maps, considering the effects of the topography on the final impacts of PDCs and lahars that were demonstrated here. Using remote sensing data to map PDC and lahar deposits from previous eruptions offers an alternative to costly and time-consuming field campaigns, and it allows for retrieval of critical parameters (e.g., erupted volumes, deposit footprint) that can be used as model confirmation and as input boundary conditions for testing computational models of PDCs. Moreover, with the growing availability of near-real-time satellites, there is potential for using the methods introduced in this dissertation to support emergency officials during and immediately after an eruption, by providing accurate extents of PDC and lahar deposits.

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