Affiliations: Physics Department, Faculty of Education, Kagoshima
University, Kagoshima 890-0065, Japan
Abstract: Typical patterns of volcanic clouds from Mt. Sakurajima are
discussed with photographs and satellite images. Volcanic clouds are classified
into three types, i.e., eruption cloud, steady flow as a plume, and sequential
puffs, according to the variation of the ejection activity with time. While the
rise of eruption clouds depends on the strength of the eruption, the vertical
shapes of the plumes are sensitive to the velocity of the cross winds around
and above the summit of the volcanic mountain. Very strong winds cause blowing
down and bouncing up of the plume along the mountain lee wave. Various patterns
of horizontal dispersion are observed from the ground and from satellites;
typical ones are linear advection, fan- and belt-type spreads, and flat
stagnation. These patterns are essentially determined by the wind shear within
the vertical thickness of the volcanic cloud.
Keywords: volcanic eruption, plume dispersion, satellite imagery, mountain lee wave