I study the structure beneath volcanoes; describe unexpected effects of the shaking from an earthquake on volcanoes; and suggest a model for a magma system. The conceivable configuration of magma systems beneath Galeras (Colombia) is studied with b- value mapping. I obtain models for earthquake- volcanoes interactions by studying drops in seismicity at Mt. Wrangell (Alaska), after the 2002 Denali Fault Earthquake. A model for the magmatic system beneath Mt. Veniaminof is proposed by modeling velocities and relocating shocks, and by studying the temporal changes of frequencies and ...