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Experimental investigation of volcanic particle aggregation in the absence of a liquid phase.

James, Mike R. and Gilbert, Jennie S. and Lane, Steve J. (2002) Experimental investigation of volcanic particle aggregation in the absence of a liquid phase. Journal of Geophysical Research: Solid Earth, 107 (B9). ISSN 2196-9356

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    Abstract

    Understanding the dispersal and deposition of fine-grained silicate particles from volcanic plumes is key to interpreting ash fall deposits and predicting hazards for future eruptions. It is known that many of these particles fall incorporated into delicate, dry aggregates whose sedimentation characteristics have not been previously investigated. Here we present the results of laboratory experiments on aggregates of small, dry silicate particles produced by the fragmentation of pumice collected from the 18 May 1980 Mount St. Helens fall deposit. The aggregation process is driven by electrostatic charges naturally imparted to the particles during the fracture process. For particle fall distances of 1 m, images of the in-flight aggregates show that they commonly have irregular shapes and are up to 800 mm in size. Strobe photography was used to determine aggregate fall velocities and, by representing aggregates as falling spheres, suggested that they had densities of c. 100–200 kg m 3. Comparable densities were obtained from experiments where equivalent fall velocities were assumed for aggregates and single particles which had been transported similar distances within a horizontal airflow. These dispersal experiments produced bimodal particle size distributions, similar to those observed in the 18 May 1980 Mount St. Helens deposits, and suggest that the aggregates were composed mainly of particles <70 mm in diameter. Our experimental results are in agreement with aggregate size and density estimates previously used within several theoretical plume sedimentation models in order to explain some features of natural ash deposits.

    Item Type: Article
    Journal or Publication Title: Journal of Geophysical Research: Solid Earth
    Additional Information: Copyright (2002) American Geophysical Union.
    Subjects: Q Science > QE Geology
    Departments: Faculty of Science and Technology > Lancaster Environment Centre
    ID Code: 13239
    Deposited By: Dr Steve Lane
    Deposited On: 09 Sep 2008 16:51
    Refereed?: Yes
    Published?: Published
    Last Modified: 17 Sep 2013 08:16
    Identification Number:
    URI: http://eprints.lancs.ac.uk/id/eprint/13239

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