Abstract The feeder dike formed by the eruption of the 1983 Miyake-Jima, Japan, is composite, based on field observations such as cooling joints and zonal arrangement of it. Three-dimensional orientation measurements on phenocrysts contained in the dike, combined with the field observations, indicate that the dike was emplaced by three magma pulses. The first and second pulses were intruded horizontally. The final pulse, however, was intruded vertically. Such directional variations are consistent with the eruptive sequence of the active centers observed during the eruption. Therefore, these techniques may be useful to determine the location of old vents and other volcanic structures.