Research output: Contribution to Journal/Magazine › Journal article › peer-review
Research output: Contribution to Journal/Magazine › Journal article › peer-review
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TY - JOUR
T1 - Experimental investigation of volcanic particle aggregation in the absence of a liquid phase.
AU - James, Mike R.
AU - Gilbert, Jennie S.
AU - Lane, Steve J.
N1 - Copyright (2002) American Geophysical Union.
PY - 2002
Y1 - 2002
N2 - 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.
AB - 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.
U2 - 10.1029/2001JB000950
DO - 10.1029/2001JB000950
M3 - Journal article
VL - 107
JO - Journal of Geophysical Research: Solid Earth
JF - Journal of Geophysical Research: Solid Earth
IS - B9
M1 - JB000950
ER -