Heat discharge from fumaroles, which is the major part of the total energy released from volcanoes at non-eruptive stage, has been estimated mainly by direct measurements of issuing mass flux and temperature. However, the direct measurements are not applicable to inaccesible areas, such as crater floors or active fumarolic zones, especially at the time of increasing volcanic activity. Hence, it is highly desirable to establish a method which can evaluate the amount of heat discharge due to fumarolic activity safely and easily. The relation between heat energy release rate Q (W) and plume rise height h(m) was given by Briggs (1969) as Q=2.6x1O⁴ h³u³x^-2, where x is horizontal distance from the heat sorce in meter and u is the horizontal wind velocity in m/sec. The above Briggs' fomula was modified as h=C t^2/3 and Q=2.6x10⁴uC³, where t is the time in second. In the above formula, heat discharge rate Q can be estimated by determining the constant C and the wind velocity u with successive photographs of desired fumarolic plume. 0n the other hand, the evaluation of mass flow of volatile components from active vents is one of the important problems of the volcanology. The amount of H₂ 0 emission can be estimated from Q based on some assumptions.

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Most of the Quaternary volcanoes in Japan are composite cones. Their surfaces are geomorphologically composed of various landform units. These fundamental units of the volcanic landfoms are classified as follows: (1) Accumulation surfaces of essential eruptive materials (original surfaces of lava flows, pyroclastic flows and pyroclastic cones) (2) Land-forms built by volcanic activities (craters, calderas, mud flow surfaces and fault scarps) (3) Landfoms formed by epigenic processes (volcanic fans, valley walls and floors, and scarps, bowls and earth flows of landslides). The original surfaces of these landforms have inherent features, such as lava wrinkles and frontal scrps of lava flows on lava flow surfaces, and pyroclastic flow levees, pyroclastic flow trench and pyroclastic flow mound on pyroclastic flow surfaces. Therefore it is almost possible to discriminate various eruptive materials through the observation of landform features with aerial photographs. It is further possible to follow the sequence of surfaces immediately adjoining each other through the features of the patterned boundary line, by the mode of contact of two accumlation surfaces with an erosional surfaces interposed between the two, and by the erosional degrees of the surfaces. The use of aerial photographs as mentioned above is available for the reduction of labor, time and expenses in the investigations of volcanic geology.

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The underground P-wave velocity structure in the Kirishima volcanic area was first proposed by Minakami et al. in 1969. Their structure, having two (parallel) layers of which velocities 4.3km/sec. (upper) and 6.1km/sec. (lower) respectively, was derived from the analysis of the seismometrical data observed during the period of the Ebino earthquake swarms in 1968. From 1972 to 1975, explosion earthquake surveys in the southern Kyushu district were carried out by the research group of the GDP. We observed these explosion earthquakes with the routine and temporal seismometrical networks of the Kirishima volcano observatory. Combining the observational data of the 1968 Ebino earthquakes with newly observed data of explosion earthquakes, the P-wave velocity structure of the Kirishima volcanic area was obtained. The results are as follows. 1) The true P-wave velocity of the second layer of the Kirishima volcanic area is 5.9km/sec. 2) The depth of the second layer is 5.Okm from the ground surface in the Okamoto area. and the upper surface of 5.9km/sec. layer has an inclination of about 2.1°dipping toward the directiod N35°W. 3) It is supposed from the observed apparent velocities of the explosion earthquakes that the surface of the 5.9km/sec. layer is slightly domed up beneath the Kirishima volcanoes, except the eastern side of the volcanoes, where the data are lacking. 4) The distribution of the hypocenters of the earthquakes which occured just beneath the area of active cones of the Kirishima volcanoes were restricted with in the upper layer (4.3km/sec.) of the newly decided velocity structure.

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