The power and limitations of analogue experiments of pyroclast fluidization and segregation: applications to ash venting and secondary pyroclastic eruptions
Abstract
There are many scenarios where gas flows upward relative to pyroclasts in and above volcanic vents, and in pyroclastic density currents (PDCs) and PDC deposits. The gas flow exerts a drag on the particles (partially) supporting their weight. With sufficient gas flow, smaller, lighter particles are transported out of the pyroclastic mixture forming a plume (e.g. ash-venting from conduits and contributing to co-PDC ash plumes). The larger, heavier particles left behind can be fluidized, that is their weight is supported but gas flow isn't strong enough to carry them out of the mixture. Fluidization can make particle currents more mobile, and it also allows them to internally mix and segregate by size and/or density. With an understanding of the relationships between gas-particle-particle interactions during volcanic processes and the characteristics and structures of the resulting deposits, the deposits can be interpreted in terms of the processes that formed them.
The gas-particle-particle interactions that control fluidization and segregation depend on the gas flux and particle properties (density, shape and size distribution). Analogue experiments for volcanic applications have built on a large body of work, mostly with spherical particles, for industrial applications. Useful experiments can be done with natural pyroclastic mixtures but it is easier to isolate the effects of individual factors with simplified analogue materials (e.g. uniform-density spheres). This talk will explore the physical insights gained into ash venting and secondary eruptions of PDC deposits from simplified analogue experiments. It will also highlight their limitations, especially with regards to particle size distributions, which affect packing, permeability and mechanical interaction among particles.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.V32A..08R
- Keywords:
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- 4314 Mathematical and computer modeling;
- NATURAL HAZARDS;
- 8414 Eruption mechanisms and flow emplacement;
- VOLCANOLOGY;
- 8428 Explosive volcanism;
- VOLCANOLOGY;
- 8445 Experimental volcanism;
- VOLCANOLOGY