Alot
Volcanoes don't help plate tectonics; volcanoes are the result of plate tectonics.
Hotspot volcanoes form over a fixed hotspot in the mantle, resulting in a chain of volcanoes as the tectonic plate moves over it, like the Hawaiian Islands. Volcanoes at plate boundaries are formed by the interaction of tectonic plates, where one plate is forced under another (subduction) or plates move apart (divergence), creating volcanic activity along the boundary, like the Ring of Fire.
Active volcanoes demonstraight the location of active plate boundries. Dormant volcanoes, such as the Japanese island chain, demonstraight how plate boundries have shifted over time.
Such volcanoes are hot spot volcanoes.
The plate boundary between the Nazca Plate and the South American Plate does produce volcanoes, earthquakes, and tsunamis. Hurricanes have nothing to do with plate boundaries.
A physcadelic plate.
No. Mars does not have plate tectonics. The volcanoes on Mars are the result of hot spots.
High mountain ranges without volcanoes are built at convergent continental plate boundaries. These vary greatly from divergent boundaries which cause volcanoes to form.
Japan has volcanoes because it lies on the edge of the Pacific tectonic plate which is being shoved under the Asian plate. As the Pacific plate descends. the increasing heat causes the rock to melt and volcanoes to erupt.
FRICTION!!!!!!!!!!!!!!!!!!!!!
Shield volcanoes may occur far from any plate boundaries.
Lava easily spews out of plate faults making volcanoes.