Here's a breakdown:

* Tectonic plates: The Earth's outer layer (lithosphere) is divided into large, rigid plates called tectonic plates.

* Asthenosphere: Beneath the lithosphere lies the asthenosphere, a layer of semi-molten rock.

* Subduction: When two tectonic plates collide, one denser plate (often an oceanic plate) is forced beneath the less dense plate (often a continental plate). This descending plate sinks into the asthenosphere, a process known as subduction.

Key points about subduction:

* Driving force: Gravity is the primary driving force behind subduction. The denser plate is pulled downwards by its own weight.

* Volcanoes and earthquakes: Subduction zones are often associated with volcanic activity and earthquakes. As the subducting plate descends, it melts, creating magma that rises to the surface.

* Ocean trenches: The point where the subducting plate bends and begins to descend is marked by a deep trench in the ocean floor.

Let me know if you'd like to know more about subduction or any other geological process!