The oceanic Jan de Fuca plate converges with the North American plate and subducts beneath it.

Tectonic plates that collide and one sinks below another is called a subduction boundary. This is the boundary that created Mount Rainer. These types of boundaries are known for making tall mountain ranges that arc along the plates. However, as the subduction plate sinks it melts to become magma that rises to the surface, which is the reason for Mount Rainer being a volcano.