A large amount of pyroclastic materials (ca. 1.7 km³) was erupted during the 1707 eruption of Fuji Volcano. Variety of lithic fragments has been recognized in the pyroclastic fall deposits, namely, accessory and accidental lava fragments, gabbros, and granitoids. A great variety of petrologic features is observed in gabbroic fragments consisting of olivine gabbro norite, gabbro norite, troctolite and anorthosite. The gabbros are divided into O, P and F groups on the basis of modal ratios of olivine, plagioclase and Fe-Ti oxide. O group mainly consists of plagioclase and olivine with minor amounts of pyroxenes and Fe-Ti oxide. O group is considered to have been adcumulated in the lower part of magma chamber because of their high depletion in incompatible elements, their well-sorted grain size and sedimentary structure. P group is composed of plagioclase, pyroxenes and minor amounts of olivine and Fe-Ti oxide. F group is similar to P group, but is enriched in Fe-Ti oxide. P and F groups are orthocumulates and may be solidified in the upper part and margin of magma chamber or dike because of their porphyritic texture. Such a variety of gabbros may correspond to the difference in location of the single gabbroic body beneath Fuji Volcano. The estimated source magma of the gabbros is similar to the basalt of Fuji Volcano in chemical and mineralogical compositions indicating that they are cognate origin. Chemical compositions of olivine and pyroxenes become magnesian and those of plagioclase become calcic with the decreasing of bulk-rock FeO^*/MgO ratio. It suggests that they are the products of continuous fractional crystallization. The magma of the 1707 eruption could have come up from under the gabbroic body, which was the solidified basaltic magma chamber, and have caught and brought the rocks from the gabbroic body up to the surface as cognate xenoliths during the eruption.

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The Sukawa lahar deposits (L1-L7), at the western foot of Adatara volcano, are made up of clay-rich matrix-supported massive breccia containing abundant hydrothermally altered andesite. The lowest L1 deposit extends 10 km from the Numanotaira crater, has a volume of 8.4 × 10⁶ m³, and covers an area of 2.8 km². This lahar occurred at 2400 y. B. P. and was presumably generated by a break of the Numanotaira crater lake during a phreatic eruption. The L2-L7 deposits, whose individual volumes are less than 4 × 10⁵ m³, fill a channel incising the L1 deposit. These lahars took place at 1600 to 860 y. B. P. The grain-size data and the ratio of drop to travel distance (H/L) indicate that the Sukawa lahars are typical cohesive lahars. The Numanotaira crater is now filled by muddy slurry, and opens directly to the Iwo-Sukawa River on the western flank. The possible cohesive lahars along the Iwo-Sukawa River should be added to the potential hazard of this volcano.

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