The summit of Kurikomayama is cut by a 4-km-wide caldera breached to the north that is partially filled by the Tsurugidake central cone, once mined for sulfur. The complex andesitic-to-dacitic stratovolcano was constructed over a relatively high basement of Tertiary dacitic tuffs and sedimentary rocks. Early stage eruptions beginning about 500,000 years ago produced lava flows to the north and south, followed by growth of the Higashi-Kurikoma (East Kurikoma) stratovolcano. Magusadake volcano on the western side of the complex was active until about 100,000 years ago. Construction of the main cone concluded with lava flows to the E, SE, and W. Daichigamori lava dome and Aguroshi-yama pyroclastic cone are located on the southern flank. A few minor phreatic eruptions from the central cone have been recorded over the past 600 years.