Geologists have incorporated volcanism into the theory of plate tectonics. Their theory says that active volcanoes obtain their energy from the movements of crustal plates. It is because of this that volcanoes tend to be associated with major plate boundaries.
Convergent and divergent are two kinds of plate boundaries where volcanoes form. When one plate plunges beneath the other, material on the upper surface of the subducted plate is dragged downward into the earth's crust until it reaches a depth where it becomes molten. It then rises and is ejected at the surface through a volcanic vent. At divergent plate boundaries, such as the Mid-Atlantic Ridge, where oceanic crust is being stretched and rifted apart, a linear zone of weakness forms.
When the volcano of Paricutín erupted in the middle of a central Mexican cornfield in 1943, scientists had the opportunity to study the birth and the order of emited materials firsthand. The lava flows completely buried the village of Paricutín.