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1. A volcanic tremor was detected in the summer.2. A flow of lava occurred from the crater at the peak to the bottom of the caldera.3. Fissure eruption, lava fountain, and lava flow occurred on the caldera floor. Fissure eruption also occurred outside the outer rim and the stream of lava flowed into the area close to the inhabited area.4. All residents (approx 10,000 people) were evacuated out of the island for about a month.1. There was an eruption from the peak; a caldera formed.2. Cinders and ash were produced.3. A low temperature pyroclastic flow was generated.4. A large amount of volcanic gases was emitted.5. All residents (approx 3,800 people) were evacuated out of the island for about 4 and half years.050km100km150kmIzu Oshima Eruption, 1986, photographed by Katsumasa Abe, University of TokyoMiyakejima Eruption, 2000, photographed by Keiji TakeiriErupted year/monthLocationNov. 1986Izu OshimaJul.‒Aug. 2000MiyakejimaSummary(3) Volcanic Eruptions　Mechanism of Volcanic Eruptions　A volcanic eruption, like an earthquake, occurs as a result of tectonic plate and mantle activities of the earth.　Volcanoes are generally found near tectonic plate boundaries (along a submarine trench, ridge, etc.), and at hotspots* in the interior of plates. For volcanoes in Japan, magma reaches the surface as rocks from the upper mantle, molten by fluids from the subducted oceanic plate, and rises and collects in magma chambers.　An eruption occurs when the volcanic crater opens and the gas pressure of the magma decreases, in turn producing gas bubbles and increasing the volume of the magma, which is forced to gush out. When the amount of gas bubbles is small, the magma gushes out as a lava flow.*Places scattered inside the plates where magma springs up from the Earth's deep mantle.　Volcanoes in Tokyo　There are 21 volcanoes in Tokyo, out of the 111 nationwide. All of them are located on its islands; there are 8 volcanic islands which are inhabited. (Izu Oshima, Toshima, Niijima, Kouzushima, Miyakejima, Mikurajima, Hachijojima, Aogashima)　The most active among them in particular are Izu Oshima and Miyakejima. In the past 100 years, Izu Oshima has had three eruptions, at 36- to 38-year intervals, and Miyakejima has had four eruptions, at 17- to 22-year intervals. Cinders, volcanic ash, lava flows, and volcanic gases have caused direct and indirect damage, often necessitating evacuation.11