Atmospheric dust dispersal analyzed by granulometry of the Misers Gold Event

Abstract

Granulometric analysis of ejecta from Misers Gold high explosive cratering experiment demonstrates that atmospheric dust dispersal can be evaluated by particle‐size distribution data. From size analyses of the Misers Gold preshot test bed alluvium, ejecta, and sweep‐up materials collected out to 35 crater radii (1227 m), we find that approximately 5.9 × 106 kg (∼11% of the total crater ejecta mass) was depleted from the crater ejecta deposits and likely represents the portion of the cratered mass initially lofted into atmospheric suspension. The dominant size range of this lofted dust was 88 to 2000 μm with a mean diameter by mass of 384 μm,. In addition to the dust lofted in the explosion column, dust in the size range of 100–800 μm was swept up from the ground by the explosive air blast and base surge dominantly between ranges of 10 and 18 crater radii (360 and 650 m from ground zero). This sweep‐up dust was convectively drawn into the column and contributed up to 2% of the total mass of lofted. Based on the measured abundance of coarse (>250 μm diameter) dust particles in the estimated lofted dust, it is likely that about 70% of this lofted mass fell out within about 1 hour, such that the remaining dust cloud mass was ∼1.8 × 106 kg, which is equivalent to a dust lofted per unit blast yield of 0.5 kT/kT or about 4% of the crater ejecta mass. This study supports the hypothesis that if initial distributions can be constrained, the volume of dust lofted into atmospheric suspension from large surface explosions can be estimated from analysis of particle‐size distributions of ejecta deposited near the explosion. This result may have particular applications to study of the atmospheric effects of historic and prehistoric volcanic eruptions.

Sequential fragmentation/transport theory, pyroclast size–density relationships, and the emplacement dynamics of pyroclastic density currents — A case study on the Mt. St. Helens (USA) 1980 eruption

“…Different PDC particle transport mechanisms have been shown to produce unique sizedensity distributions at the outcrop scale, enabling the reconstruction of parent current processes using physically-based SFT model functions and descriptive parameters (e.g., Wohletz, 1989;Orsi et al, 1992;Wohletz and Raymond, 1993;Wohletz and Brown, 1995;Wohletz, 1998;Taddeucci and Palladino, 2002). We interpret the SFT data trends described above in terms of particle transport mechanisms and depositional conditions, and examine the extent to which the deposit information provided using SFT analysis coincides with the field observations and interpretations made based on the excellent MSH deposit exposures (e.g., NOTICE: this is the author's version of a work that was accepted for publication in Journal of Volcanology and Geothermal Research.…”

“…Additionally, previous studies indicate that model functions produced using SFT analysis fit the size-frequency curves of pyroclastic deposits more accurately than lognormal functions (Wohletz et al, 1989;Orsi et al, 1992;Wohletz and Raymond, 1993;Brown and Wohletz, 1995;Taddeucci and Palladino, 2002).…”

“…5). When plotted against each other, the weight fraction, mode, and dispersion parameters can be used to attribute the different subpopulations to specific particle transport and emplacement mechanisms (e.g., Wohletz et al, 1989;Orsi et al, 1992;Wohletz and Raymond, 1993;Wohletz, 1998). See NOTICE: this is the author's version of a work that was accepted for publication in Journal of Volcanology and Geothermal Research.…”