抄録
The geomorphological characteristics of volcanic products and its volume of the 1986 eruption of Izu-Oshima volcano were clarified as follows based on the careful interpretation from aerial photographs and large scale maps of pre- and post-1986 eruption, and photogrammetric measurement of topographical change : 1. Distribution of 1986 craters, cinder cones and lava flows were represented carefully on a map considering their accurate topographic positions and micro-landforms. 2. Arrangement of 1986 craters is in left lateral echelon, whose position is coincident with the zone of flank volcanos and craters. 3. LB I and III lavas, erupted and flowed by breaking the cinder cones, have distinguishing features. Their surface structure and color tone are different from those of LA lava. 4. LB II lava was effused by forcing through the agglutinated cinder cone two days after the fissure eruption. Other part of cinder cone was swelled out toward the lower slope. 5. The discolored water areas around the Izu-Oshima seem to have occurred repeatedly prior to the 1986 eruption, by the slope failures, heavy rainfall or turbulent sea. 6. The total mass of volcanic products through the 1986 eruption (except vapor-phase materials) is estimated to be about 7.9×107 tons. The details are as follows : 3.5×107 tons through Nov. 15～19, 4.4×107 tons on Nov. 21. 7. Among the volcanic products mentioned above, the scoria fall deposit is distributed in the eastern part of the island. Its mass is estimated to be about 9×106 tons, including those fallen of the sea surface. The volcanic ash deposited in very small amount, and the most was swept away within a few days. 8. The mass of volcanic products through the 1986 eruption slightly exceeds than that of the 1950・1951 eruption.
