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Characterizing Volcanic Ash Density and its Implications on Settling Dynamics
  • Sing Lau,
  • Roy Gordon Grainger,
  • Isabelle Alice Taylor
Sing Lau
University of Oxford

Corresponding Author:[email protected]

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Roy Gordon Grainger
University of Oxford
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Isabelle Alice Taylor
University of Oxford
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Volcanic ash clouds are carefully monitored as they present a significant hazard to humans and aircraft. The primary tool for forecasting the transport of ash from a volcano is dispersion modeling. These models make a number of assumptions about the size, sphericity and density of the ash particles. Few studies have measured the density of ash particles or explored the impact that the assumption of ash density might have on the settling dynamics of ash particles. In this paper, the raw apparent density of 23 samples taken from 15 volcanoes are measured with gas pycnometry, and a negative linear relationship is found between the density and the silica content. For the basaltic ash samples, densities were measured for different particle sizes, showing that the density is approximately constant for particles smaller than 100 μm, beyond which it decreases with size. While this supports the current dispersion model used by the London Volcanic Ash Advisory Centre (VAAC), where the density is held at a constant (2.3 g cm−3), inputting the measured densities into a numerical simulation of settling velocity reveals a primary effect from the silica content changing this constant. The VAAC density overestimates ash removal times by up to 18%. These density variations, including those varying with size beyond 100 μm, also impact short-range particle-size distribution measurements and satellite retrievals of ash.
13 Jan 2024Submitted to ESS Open Archive
13 Jan 2024Published in ESS Open Archive
28 Jan 2024Published in Journal of Geophysical Research: Atmospheres volume 129 issue 2. 10.1029/2023JD039903