S (the synodic period) = 360 / (360/ P - 360/365.256) days. S (the synodic period) = 360 / (360/365.256 - 360/ P) days. A diagram showing the relationship between orbital size and synodic periods. As the planets move around the Sun they change their positions relative to each other.
Some geologists consider that mantle plumes are generated in the lower levels of the asthenosphere by the decay of concentrations of radioactive isotopes. However, many believe that they are generated at much deeper levels in the lower mantle, perhaps even at the boundary of the mantle with the outer core.
Where one plate is being subducted under another, chambers of magma may form. These magma bodies feed the volcanic islands that mark subduction zones. Although most volcanic activity takes place at plate boundaries, volcanism also can occur within the plate interiors at hotspots. Hotspots are thought to be from large âplumesâ of extremely hot material rising from deep in Earth's interior.