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.
Tsunamis can actually occur anywhere, but there are areas of the world where they are more likely to happen. Most Tsunamis occur around the Pacific Ocean due to high seismic activity. Japan, for example, is so prone to Tsunamis, that they even practice 'Tsunami Drills'.