Final answer:
The boundary between the Juan de Fuca Plate and the North American Plate is a convergent plate boundary characterized by the subduction of the Juan de Fuca Plate, leading to the formation of the Olympic Mountains and volcanic activity in the Cascade Range.
Step-by-step explanation:
The Olympic Mountains located along the west coast of the United States are formed at the boundary between the Juan de Fuca Plate and the North American Plate. This boundary is a convergent plate boundary, where the denser oceanic Juan de Fuca Plate is subducting, or moving underneath, the lighter continental North American Plate. The subduction process at convergent boundaries is responsible for creating mountain ranges like the Olympic Mountains and also leads to volcanic activity, as seen in the formation of the Cascade Range, which includes Mount St. Helens.
The ultimate fate of the Juan de Fuca Plate, given its current rate of movement, is to be fully subducted beneath the North American Plate, diminishing its size over time. The tectonic processes that formed the Cascade Range were also due to subduction, where the Juan de Fuca Plate descends below the North American Plate, causing melting in the mantle and leading to volcanic eruptions that contribute to the building of the range.