At the subduction zone of the Juan de Fuca and the North American tectonic plates, the Juan de Fuca plate is subductiong below the North American one, going downwards toward the mantle and being melted in it.
Once a very large tectonic plate, the Juan de Fuca plate is now only a small fraction of its peak size. It is actually not even in one piece, but it is broken down into three smaller plates, though very often all of them go under the same name. This plate is of oceanic type, making it lower and denser than the continental plates such as the North American. Because it is lower and denser, the Juan de Fuca plate is subducting below the North American plate, slowly disappearing from the face of the Earth, getting down into the mantle where it is melted and recycled.
This subduction zone is causing a lot of geological activity in the area, with the earthquakes and the volcanic activities being a regular occurrence. Also, this subduction zone is responsible for the formation of the mountain chains in the western apart of North America, such as the Rocky Mountains and the Cascade Mountains.
