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The density, construction and drag coefficient of electrostatic volcanic ash aggregates.

James, Mike R. and Lane, Steve J. and Gilbert, Jennie S. (2003) The density, construction and drag coefficient of electrostatic volcanic ash aggregates. Journal of Geophysical Research: Solid Earth, 108. p. 2435. ISSN 2196-9356

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    Abstract

    Recent laboratory experiments have demonstrated that electrostatic charges generated during the fragmentation of volcanic pumice cause rapid aggregation of the silicate particles produced. Here, we present measurements of the mass and component particle size distribution of individual, electrostatically bound aggregates produced during these experiments. Particles produced by fracturing pumice aggregated as they fell ∼1.5 m within an enclosed fall chamber. Aggregate mass measurements indicate aggregate densities of ∼200 kg m−3 or less. The component particle size analysis demonstrates exponential-type cumulative distributions which are dominated (on a volume basis) by particles ∼10–40 μm in diameter and contain few particles >70 μm. By representing these particles as disks of 5 μm thickness the calculated aggregate densities are in agreement with those derived from the aggregate mass measurements and indicate a relatively constant aggregate density with size (in contrast with previous results from fall velocities). Combining the density measurements with fall velocity data allows the drag coefficient of aggregates to be determined. Empirical equations developed to describe the particle size distribution within aggregates are used to derive relative aggregation coefficients for the electrostatic aggregation process. Our results can be used within numerical models of volcanic plumes in order to improve their representation of electrostatic aggregation processes.

    Item Type: Article
    Journal or Publication Title: Journal of Geophysical Research: Solid Earth
    Additional Information: Copyright (2003) American Geophysical Union.
    Subjects: Q Science > QE Geology
    Departments: Faculty of Science and Technology > Lancaster Environment Centre
    ID Code: 1457
    Deposited By: Dr Mike R. James
    Deposited On: 11 Feb 2008 16:54
    Refereed?: Yes
    Published?: Published
    Last Modified: 17 Sep 2013 08:16
    Identification Number:
    URI: http://eprints.lancs.ac.uk/id/eprint/1457

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