A synodic year is the time it takes for a planet-sun alignment to reoccur. For the case of the sun, it is the time it takes the sun to come to the same place on the ecliptic (equinox to equinox) and is called a Tropical Year. A tropical year is 365.242 mean solar days (366.242 sidereal days). It is just over 20 minutes shorter than a sidereal year (again, the effect of precession). Because a tropical year is 365.242 mean solar days long, the vernal equinox would be later and later every year if our calendar year were strictly 365 days long.
Let's review. Mantle plumes are hypothesized columns of hot mantle rocks that rise through the mantle from the mantle-core boundary to the base of the lithosphere. The lower lithosphere rocks are heated by the plumes and melt to form hot spots.
ANS: Most volcanoes occur at either divergent plate boundaries at ocean ridges or rifts; at convergent plate boundaries at subduction zones; or at hot spots, which are not plate boundaries, but are areas where hot mantle plumes cause volcanic activity.PTS: 1 DIF: L2 OBJ: 10.8 16.ava plateau____ 8. At divergent plate boundaries in the ocean, magma rises and melts because of ____.a. higher temperatures at the surface c. intrusive plutons at the boundaryb. a decrease in pressure d. increased silica content of magma____ 9.