Earthquakes and volcanoes are both the result of the movements of earth's tectonic plates. Volcanoes tend to occur where two plates either push together or pull apart and cause the crust to thin and ultimately rupture. Then magma and hot gasses can vent to the atmosphere. Earthquakes occur when the movement of tectonic plates build up enough stress over time that it causes the built up energy to be release by the movement along fault lines, thus releasing seismic energy.
All earthquakes and volcanoes ultimately occur for these reasons. Unfortunately seismic activity is essentially impossible to predict ahead of time. A famous example of an American volcanic eruption is Mt. Saint Helens in Washington in 1980. A famous American earthquake is the San Francisco earthquake of 1906.