I've had this question before so i know the answer is:
<span>Mount st. Helens and the other cascade volcanoes are young, active volcanoes built on a continental margin above a sinking slab of oceanic plate. </span> Hope This Helps You! Good Luck :)
Mount st. helens and the cascade volcanoes present in Skamania County, Washington. The most effective and notorious eruption of this volcano had occurred on May 18, 1980.
These volcanoes are quiet young and active strato volcanoes. They are mainly built on the continental margin that are marked above the sinking slab of the oceanic lithosphere. The layers of volcano also consists of the of basalt and andesite.
