Volcanoes mostly form where Earth’s tectonic plates are moving apart, colliding, or above especially hot areas in the mantle.

The main places volcanoes form

1. Divergent plate boundaries (plates moving apart)

At divergent boundaries, two plates pull away from each other, letting hot mantle rock rise and melt into magma, which then erupts to form new crust.

  • Common along mid‑ocean ridges under the sea.
  • Example: The Mid‑Atlantic Ridge, where magma erupts as pillow‑shaped basalt lavas on the ocean floor.
  • On land, places like Iceland sit on such ridges, with many active volcanoes.

2. Convergent plate boundaries (plates colliding)

At convergent boundaries, one plate (usually oceanic crust) sinks beneath another into the mantle in a subduction zone, carrying water and sediments down with it.

  • The added water lowers the melting temperature of mantle rocks, generating magma that rises to form volcanoes in chains called volcanic arcs.
  • Ocean–ocean collision: creates island‑arc volcanoes (for example, the Mariana or Aleutian arcs).
  • Ocean–continent collision: creates big continental volcano chains, like the Andes or Cascades.

3. Hot spots (in the middle of plates)

Some volcanoes form away from plate boundaries above “hot spots” – focused plumes of very hot mantle rising from deep inside Earth.

  • The plume melts the overlying plate, producing repeated eruptions that can build large shield volcanoes.
  • As the tectonic plate slowly moves over the fixed plume, it creates a chain of progressively older volcanoes.
  • Classic example: The Hawaiian Islands, formed as the Pacific Plate moved over the Hawaiian hot spot.

4. Where volcanoes do not usually form

Volcanoes are rare at transform (side‑slipping) boundaries, where plates slide past each other, because there is little or no magma being generated there.

In short, volcanoes form mainly where plates diverge , where they converge and one subducts, or above mantle hot spots deep beneath the moving plates.

TL;DR: Most volcanoes form along divergent and convergent plate boundaries, plus a smaller number over hot spots in the middle of plates; they almost never form at transform boundaries.

Information gathered from public forums or data available on the internet and portrayed here.