Rise and flow of volcanic clouds observed from the ground and from satellites

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.