Movements of tectonic plates ??

Question

the question is :

How come that movement of tectonic plates will produce sometimes volcanoes and sometimes mountains ?

Answer 1

For the same reason that someone driving a car on the sidewalk will produce sometimes knocked down mailboxes and sometimes knocked over fruit stands.  It all depends on what the car hits and how it hits it.

Answer 2

It all depends on what the plate boundaries are composed of, how hard and fast they are pushing into each other, and if there is a plume located underneath in the mantle. India, to be sure, produced many volcanoes as well as the Himalyas. If the plate is moving over a plume in the mantle, it will produce a successive chain of volcanoes. The Emporer Seamounts are prime examples of this, (Hawaiian Islands are the result).