The cause of volcanic eruptions is simply magma finding a path out on to the surface of the Earth crust. These paths are usually cracksfissures in the crust, due to the movement plate tectonics. Magma being lighter in density than the surrounding rock, eventually comes to the Earth’s surface. The actual eruption is of two types:
1. The lava is acidic and in nature and viscous. The lava flow is slow and thick and therefore has greater pressure. The resulting eruption is explosive. Mt. Pinatubo in the Philippines is an example.
2. The lava is highly fluid and of darker color. It flows larger distances and forms basalt plateaus. Mauna Kea in Hawaii is an example.