Observation of flow and dispersion of volcanic clouds from Mt. Sakurajima

A brief overview is presented concerning the rise and atmospheric diffusion of volcanic clouds from Mt. Sakurajima in Kyushu, Japan, mainly in the altitudes 1–4 km above the sea level, on the basis of remote sensing data from satellites and visual data of video records and photo pictures. Rising pattern of the cloud is determined by the ejection strength of the volcano and wind velocity in the free atmosphere. Occasional eruption forms a column which develops almost vertically within a few minutes, and drifts away dispersing slowly. Continuous ejection of the cloud forms a stationary plume which rises with an angle according to the wind velocity, and flows horizontally at an equilibrium height with the ambient atmosphere. Dispersion patterns of the clouds are understood in relation to the vertical shear of upper winds in the concerned altitudes. Typical ones are linear advection, fan-type spread and belt-type diffusion.