Josef Dufek
Georgia Institute of Technology
Explosive volcanic eruptions produce turbulent, multiphase flows that encompass a vast range of scales from micron-scale ash to eruptive plumes that can extend 100s of kilometers. One of the fundamental challenges in understanding these events is reconciling the role of microphysical process (e.g. at the scale of individual particles) with the macroscopic dispersal of pyroclasts in plumes and pyroclastic flows. Recent modeling efforts and long established observations of deposits have demonstrated that quasi-persistent flow structures can develop in these eruptions and particles of different size and density can be concentrated as a result of coupling with these structures. Yet due to limited resources, computational and conceptual models have focused on the large-scale structures of bulk material rather than local interactions that may ultimately produce emergent dynamics that result from mass, momentum and heat exchange at small scales.
Subgrid models of microphysical processes provide a way to link local processes to large-scale dynamics. I will discuss the role of laboratory experiments in developing these subgrid relations and as a way to better understand the underlying physics. As these experiments are focused on only small parts of these flows, they can often be conducted under conditions similar to those experienced in natural flows. Three microphysical processes that occur during explosive volcanic eruptions will be examined that exemplify mass, momentum, and energy transport at the very smallest scales of these flows: 1. particle breakup (comminution), 2. momentum transfer due particle-particle and particle-boundary collisions, and 3. steam explosions that result from short-duration heat transfer between particles and a water source, such as the sea. For each of these examples, I will discuss the field evidence for these processes using the examples of the Kos Plateau Tuff eruption, the eruption of Mount St. Helens in 1980, and dome-collapse eruptions at Montserrat.
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Department of Geosciences
Virginia Polytechnic Institute and State University
4044 Derring Hall (0420)
Blacksburg, VA 24061