Most of active volcanoes in Japan formed stratovolcanoes or complex volcano. These volcanoes potentially produce the volcanic hazards such as pyloclastic flows, laha, volcanic bombs, ash falls potentially that travel faster and longer distances.  Because Japan volcanic-arc is linked to the Cascade Volcanic-arc by the Ring of Fire, the volcanic hazrds in Japan are very similar to the hazards in the Cascade volcanoes, for example Mt. St. Helens eruption in1980 (1).  Some of those volcanoes are located near highly populated areas.  People in areas often face to the serious volcanic hazards when the volcanoes erupt, for example Unzen and Sakura-jima volcanoes.   

                         Map of major volcanoes in Japan (USGS)

(1) R S Bernstein, P J Baxter, H Falk, R Ing, L Foster, and F.  "FrostImmediate public health concerns and actions in volcanic eruptions: lessons from the Mount St. Helens eruptions, May 18-October 18, 1980."Am J Public Health. 76(Suppl): 25–37, 1986 March.  

(2) Map courtesy of the USGS “Major Volcanoes in Japan.”  May 13, 2003.