Volcanism is primarily caused by which geological phenomena?

Volcanism is primarily associated with the movement of tectonic plates, and the development of new ocean crust at divergent boundaries is a fundamental process in this phenomenon. At divergent boundaries, tectonic plates move away from each other, allowing magma from the mantle to rise to the Earth's surface. This creates new crust as the magma cools and solidifies, which is a key characteristic of volcanic activity.

The formation of new ocean crust is directly linked to volcanic eruptions that occur at mid-ocean ridges, where magma consistently emerges and forms new geological material. The resulting volcanic activity is responsible for not only the creation of new crust but also for the significant geological features associated with ocean basins.

While plate tectonics and earthquakes also play a role in volcanism, the option specifically highlighting the development of ocean crust at divergent boundaries more precisely captures the primary cause of volcanism. Other choices, such as weathering of continental rocks or glacial movements, are unrelated to the processes of magma movement and volcanic eruptions, further emphasizing the correctness of the selected answer.