Three major events take place at plate boundaries: the formation of volcanoes and mountains, and a greater occurrence of earthquakes. There are also three main types of plate boundaries: divergent, convergent and transform.
Plates consist of oceanic crust and continental crust. Volcanoes form at divergent boundaries in which two plates move away from each other, and new crust is created by magma pushing up through the Earth's mantle. The best-known divergent boundary is the Mid-Atlantic Ridge, according to the United States Geological Survey. As a submerged mountain range, it extends from the Arctic Ocean past the southern tip of Africa. Earthquakes occurring at divergent boundaries are typically small and infrequent.
Convergent boundaries are responsible for building volcanoes and mountains. When two plates move toward each other, one slips under the other. This is known as oceanic-continental convergence, and it produces the most frequent, intense earthquakes.
The area where the dense oceanic crust moves under the less dense continental crust is known as the subduction zone. The Aleutian Islands region of Alaska is one example of this type of convergence. Continental-continental convergence creates some of the tallest mountains in the world, such as the Himalayan mountain range, when two continental plates move towards each other and collide.
The zone between two plates sliding horizontally past each other is known as the transform plate boundary. One of the most renowned is the San Andreas Fault, separating the North American plate to the east and the Pacific plate to the west.