A volcano  is an opening, or rupture,in planet’s surface or crust, which allows hot magma, volcanic ash and gases to escape from below the surface.Volcanoes are generally found were tectonic plates are diverging or converging.  A Mid Ocean Ridge,has example the Mid Ocean Ridge, has examples of volcanoes caused by divergent tectonic plates pulling apart; the Pacific Ring of fire has examples of volcanoes caused by convergent tectonic plates coming together.  By contrast, volcanoes are not usually created where two tectonic plates slide one another.  Volcanoes can also form were there is stretching or thinning of the Earths crust in the interiors of plates, e.g., in the east African rift, the wells gray- clear water volcanic field and then Rio Grande Rift in North America.  This type of volcanism falls under the umbrella of ” Plate hypothyisis” volcanism.