Iwakisan volcano, symmetrical on all but its western flanks, has been called the Fujisan of the Tsugaru district. The 2-km-wide summit crater is filled by a lava dome flanked by six explosion craters. Three lava domes are found on the western and southern flanks of the andesitic volcano, the NW-most active volcano in Honshu. Historical eruptions have been reported here since 1600 CE and have consisted primarily of small-to-moderate phreatic explosions.