What geological process is responsible for the formation of Mount St. Helens?

The formation of Mount St. Helens is primarily attributed to oceanic-continental convergence. This process occurs when an oceanic tectonic plate converges with a continental plate, leading to the subduction of the denser oceanic plate beneath the lighter continental plate. In the case of Mount St. Helens, the Juan de Fuca Plate (an oceanic plate) is being subducted beneath the North American Plate (a continental plate).

As the oceanic plate descends into the mantle, it leads to the melting of both the oceanic crust and some of the overlying continental crust, creating magma. This magma rises to the surface, eventually resulting in volcanic activity. Mount St. Helens is a stratovolcano that has been highly active due to this type of tectonic activity, which is characterized by explosive eruptions fueled by the accumulation of high-viscosity magma that can produce a range of volcanic features.

This geological process is crucial for understanding not just Mount St. Helens, but also many other volcanic formations worldwide, particularly those located at convergent boundaries between oceanic and continental plates.