Why does the San Andreas Fault cause earthquakes but few volcanic eruptions?

The San Andreas Fault is a transform, or strike-slip, fault where the Pacific and North American tectonic plates slide laterally past one another. This movement is "conservative," meaning it occurs without the creation or destruction of crust. Because the plates are simply sliding horizontally, there is no subduction (where one plate sinks beneath another) or rifting (where plates pull apart) to generate the molten rock necessary for volcanic activity.12345

Earthquakes occur along the San Andreas Fault because the fault surfaces are not smooth; as the plates move, they often become locked, causing stress to accumulate. When this stress eventually exceeds the strength of the rocks, it is released suddenly, resulting in seismic waves. In contrast, volcanoes typically form at convergent boundaries through subduction or at divergent boundaries through rifting, both of which provide the mechanisms for magma to reach the surface. Consequently, while the San Andreas Fault is highly prone to earthquakes, it lacks the geological conditions required to produce volcanic eruptions.2354