the volcano remained dormant until it erupted again in November 1990. It started with a slowly building active phase in 1968, with first earthquake swarms continuing until 1975. Large amounts of volcanic gas were ejected by Fugen, which affected about thirty cedar trees. In 1975, bird and animal carcasses were found in the surrounding area, and high concentrations of carbon dioxide were detected emitting from rock fractures. This area was also reported to have erupted volcanic gasses during the 1792 eruption. Earthquakes occurred sporadically from 1975, but there were 89 sensitive earthquakes, with strong shaking equivalent to a maximum seismic intensity of 5 from June to September 1979. At Shimabara Onsen, there was a place where the dissolved carbon dioxide concentration rose sharply from 1975 and increased by 30%. From April 1984, swarms occurred in Tachibana Bay A magnitude 5.7 earthquake with a seismic intensity of 5 occurred in August near the south side of Hayama. As a result of this earthquake, uplift of the Shimabara Peninsula was observed, and magma supply from Tachibana Bay began. In November 1989, an earthquake swarm began about underneath and west of Fugen-dake. Over the following year, earthquakes continued, and their hypocentres gradually migrated towards the summit. Finally on November 17, 1990 (Heisei 2), the first phreatic, or steam-blast, eruptions began ejecting from two places near a shrine at the summit. These eruptions only allowed vaporized hot water and ash to blow up from the two craters. In December of the same year, the volcano's state lulled and it seemed that it would end, but it erupted again on February 12, 1991, and on April 3, and 4th. The eruption intensified on May 9. On May 15, the first debris flow caused by accumulated volcanic ash at the summit occurred, and a number of cracks were formed on the west side of the crater, extending in an east–west direction. After this inflation of the summit area, fresh lava was confirmed to be emerging on May 20, 1991. The lava was so viscous that it did not flow out, but instead became a dome which formed in the crater. The lava dome grew like a peach, eventually splitting and collapsing into four pieces under its own weight. After that, the dome continued to grow, continuously supplied with fresh lava from the crater underneath, creating new lobes that hung down from the summit. The 1st to