Why are volcanoes not found on collision boundaries?

Answer 1

There is no subduction at a continental-continental convergent boundary. When an oceanic plate meets a continental plate or a younger oceanic plate it is forced down into the mantle. Seawater and other "volatiles" it takes with it alter the chemistry of the hot mantle rock, causing some of it to melt and rise toward the surface to form volcanoes. Continental crust is not dense enough to subduct, so no volatiles enter the mantle.

Answer 2

=== === Transform and continent to continent plate boundaries do not involve the subduction of a plate. Volcanoes can form at oceanic to oceanic plate, and oceanic to continental plate subduction zones where the presence of water in hydrous minerals which are being subducted can speed melting of some minerals. Other crystals that would be solid at a deeper depth can melt in a high-temperature, subducting environment. The resulting partial melt can carry unmelted material upward, where lower pressure allows more melt to occur. This process can occur all the way up to volcanic eruption. Without subduction there is no melt (except for rifts and hot spots).

Answer 3

Volcanoes do in fact form on collision boundaries! A very good example of this sort of volcanism is that which occurs in the Andes along the western edge of South America due to the subduction of the Nazca plate under the South American plate.

Answer 4

Volcanoes form at both convergent and divergent boundaries. At convergent boundaries (except those involving two continental plates) one plate slides under another, introducing volatiles into the mantle, which allows some of it to melt and rise to form volcanoes.
At divergent plate boundaries the young, thin crust reduces pressure on the upper mantle, reducing melting points and allowing magma to form. However, most volcanoes at divergent boundaries are deep underwater and so they usually are not noticed.

Answer 5

Continental blocks are very thick, and when they collide, they shove their mass at each other. Both continental blocks being about the same density, neither of them sinks under the other. The continental blocks continue to push against each other, creating high mountain ranges such as the Himalayas. This creates a very thick layer of rock that magma simply can't melt through.

Answer 6

because continental crust is really thick so it is not pushed up like a oceanic crust would do if it collided with the continental one. instead it crumbles up to make mountain ranges.

Answer 7

Oceanic plates are heavier and more dense so they tend to sink into the asthenosphere more. While continental plates are lighter and less dense so they don't sink downwards.

Answer 8

Continental crust is not dense enough to subduct.