Volcanoes on Plate boundaries

There are three main types of plate boundaries: divergent, convergent, and transform. Divergent boundaries occur where plates are moving apart. The volcanoes that form along such boundaries are generally nonexplosive and have new basaltic magma filling the widening separation or feeding lava flows. Even though most of the earth's volcanism occurs along divergent boundaries, the eruptions often occur unobserved because divergent boundaries are covered by the oceans, except those in Iceland and East Africa. Convergent boundaries separate plates that are moving toward each other. Most of the world's above-sea volcanoes are located along such boundaries, which are also called subduction zones. Although composite volcanoes near subduction zones produce only about 15 percent of global volcanism, they account for more than 80 percent of documented historical eruptions, mostly explosive. Transform boundaries are areas where one plate is grinding horizontally past another. These boundaries are often zones of frequent earthquakes, but they are not volcanically active.