The movement of large plates and the formation of volcanoes are primarily caused by plate tectonics. Plate tectonics is a scientific theory that describes how the outer shell of the Earth, known as the lithosphere, is divided into several large and small plates that move and interact with each other.
These plates sit on the semi-fluid layer called the asthenosphere, which lies beneath the lithosphere. The movement of these plates is driven by the convection currents within the asthenosphere. These convection currents are caused by the heat generated from the Earth's core and the radioactive decay of elements within the mantle.
When two plates interact at their boundaries, it can lead to different types of plate movements. There are three main types of plate boundaries:
1. Divergent Boundaries: Here, two plates move away from each other. This results in the formation of new oceanic crust and the upwelling of magma from the mantle. The volcanic activity associated with divergent boundaries often forms underwater volcanic ridges or mid-oceanic ridges.
2. Convergent Boundaries: In this case, two plates collide with each other. Depending on the types of plates involved, different processes occur. If an oceanic plate collides with a continental plate, the denser oceanic plate will be forced beneath the continental plate in a process called subduction. This subduction leads to the formation of a deep ocean trench and volcanic activity on the continental side, establishing mountain ranges and volcanoes. In the case of two oceanic plates colliding, one of the plates is subducted beneath the other, forming island arcs and volcanic activity.
3. Transform Boundaries: Here, two plates slide past each other horizontally. These boundaries are characterized by intense earthquakes but do not usually lead to volcanic activity.
In summary, plate tectonics is responsible for the movement of large plates and the subsequent formation of volcanoes. The specific type of plate boundary determines the nature and location of volcanic activity along with other geological phenomena.