The primary focus of Weston Observatory is on the study of earthquakes. But volcanic eruptions are, of course, another dramatic example of how active our planet is. Like earthquakes, most of the worlds's active volcanoes are associated with plate boundaries. Volcanoes are particularly common at "subduction zones", where one plate dives beneath another. Volcanoes also occur at "divergent plate boundaries", where two plates move away from each other and magma erupts from the Earth's interior. Molten rock also erupts unto the surface at certain, special spots in plate interiors known as "hot spots" that are not near subduction zones or divergent boundaries.
For an excellent source of information about volcanoes and volcanic eruptons, go to the website of the Smithsonian Institution's Global Volcanism Program.