The gigantic column of volcanic smoke may be regarded as a free jet that gushes out into the semi-infinite atmosphere. The diameter of the vortex-ring in the smoke is nearly proportional to height (Sakurajima 1946), and this means that the average mixture-length (G. I. Taylor’s definition) is proportional to height. Velocity distribution within such a free jet should be: dz/(dt)∽1/z, or z∽t^0・5. Actual examples of rise of explosion-smokes of Asama give the empirical relation z∽t^0・6. Temperature distribution within the jet is expected to be T-T_air∽1/z, if the Prandtl number is taken as 1. Actual T-distributions, measured at several vigorous solfataras, agree well with the relation. Volcanic smokes rise higher nearly in proportion to the initial velocity of the bombs. This is also explained well by the proposed jet-model. The Wolff’s idea, in which the gas is assumed to expand “adiabatically” needs alterations. Volcanic smoke is the phenomenon which should be treated as turbulent motion. The buoyancy of gas, the effect of which was not taken into account explicitly in the present theory, should be considered too.

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The vertical displacement of the earth's crust in the neighbourhood of Sakurazima Volcano at the time of the 1914 great eruption is studied on the basis of the results of precise levelling. This depression of the earth's crust is reasonably explained as the elastic deformation which is caused by the pressure decrease of a spherical pressure source at the depth of 10km from the surface. And this pressure source does not exist under the Sakurazima Volcano, but at the center of Aira Caldera (Kagoshima Bay) 10km north of the Sakurazima crater. The relation between the crustal deformation and the eruption may be considered as follows. Before the eruption, the magma reservoir (pressure source) was at high pressure and the pressure decreased owing to the outflow of lava at the time of eruption. As the result of that, the surface of the earth's crust was depressed . After the eruption, the earth's surface which subsided at the time of the eruption began to rise and the upheaval continued for several years. The phenomenon suggests the increase of pressure of magma reservoir. In addition the writer discussed the close relations between the increase and decrease of the pressure of the lava reservoir and the eruptions of Sakurazimincreosea Volcano.

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Theterm “magma” as a chemical system is used to include all naturally occurring mobile rock matter that consists in noteworthy part of a liquid phase. Formation of magma is caused by heating or decreasing of pressure, and extinction of magma is caused by cooling. End products of fractional crystallization of magma by cooling include not only the igneous rocks, but also a gas phase and possibly a watery solution. The chemical properties of the original silicate magma in the Earth derived from V. M. Goldschmidt’s hypothesis and the characteristics of the magmas formed successively in the Earth from H. C. Urey’s hypothesis are estimated from geochemical point of view. The quantity of the granite magma derived from the original silicate magma is very small, and the large amount of basic rocks in the deep place as far as more than about 1000km of the Earth is indispensable for the genesis of the granite shell in the surface of the Earth. Along with the formation of the granitie magmas in the surface of the Earth a large amount of chemical elements of the residual magma also is collected in the Earth’s crust.

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The fact that the volcanic zones are notably localized on the Earth's surface is not so far explained well enough, though several studies have been made about the mechanism of production of liquid magma. The process proposed in the present paper will be the fundamental process which results in the localized activity of volcanism. We suppose that our system is of single component, which consists of two magma reservoirs connected by a channel. The interaction of heat flow and flow of matter through the channel and phase transformation in each reservoir give rise to certain cross-phenomena, of which the most important one is that occurs when there is a gravitational potential difference between the two reservoirs. In this case the liquid magma becomes to be localized to the reservoir of higher gravitational potential. In the present paper the above process is studied by the method of irreversible thermodynamics, and the rate of increase of liquid magma at the reservoir of higher potential is derived. with some assumptions the rate J* can be expressed as J* = kAT/(Q^2)(Δυ/υ)(1-Δυ/υ)Δφ/l here κ; thermal conductivity T; absolute temperature υ; specific volume Δυ; increase of specific volume by fusion Q; latent heat A; cross-sectional area through which heat flows l; length of the channel Δφ; difference of gravitational potential. The value of the rate derived by the above formula is found to coincide, at least in its order, with the observed value. The geographical relation between the distribution of gravity anomalies and that of volcanoes may be explained by the process proposed here.

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The pyroclastic flow is defined as the flow of high-temperature, essential, fragmental materials. This is a synonym of the nuee ardente in the broad sense. Three modes of emplacement of high-temperature, essential, solid (or liquid) materials after the ejection from the crater may be recongized: 1) Projection of the fragments from the crater by the explosive expansion of gas which occurs within the crater. 2) Descent of the fragments or liquid magma from the crater which is caused only by the action of gravity. 3) Swift downflow of the mixture of gas and fragments. This is intermediate between 1) and 2) and to this corresponds the pyroclastic flow. A new classification of the pyroclastic flows is proposed. The principle is based upon the viscosity of the materials, which is inferred from the nature of the deposit. The volume of the deposit increases as the viscosity decreases. 1) Nuee ardente in the strict sense. Represented by the nuees ardentes of Mt. Pelee, Merapi, etc. The fragments are less porous, which indicates the high viscosity. The volume of the deposit is small, generally less than 0.01km³. 2) Pyroclastic flow of the intermediate type. Represented by certain pyroclastic flows of Asama. Hakone. Myoko Volcanoes. The viscosity and volume (0.1～1km³) are both intermediate between 1) and 3). 3) Pumice flow. Represented by pumice and tuff flows of all sizes, such as those of Crater Lake, Hakone, Katmai. Aso Volcanoes. Low viscosity leads to the full vesiculation into pumice. Many of them are larger in volume (＞10km³) than 1) and 2), and the caldera of Krakatau type is often formed after the eruption of larger pumice flows.

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