Question

Why do volcanoes from tectonic plate boundaries ?

Answer 1

Because the magma breaks through the crust at the places where volcanoes are found creating plant boundaries.

Answer 2

Well the divergent boundary, occurs most often at mid-oceanic ridges. Here, two plates move away from each other, forming a break, or rift, in Earth's crust. Magma from the mantle rises to fill the gap, creating new crust.

Hope it helps