Mount St.Helens and the other Cascade volcanoes from Mt.Shasta in northern California to Mt.Garibaldi in southwestern B.C.are ________.
A)young, active composite volcanoes built on a continental margin above a sinking slab of oceanic lithosphere
B)a row of young, active, shield volcanoes built as western North America moved over a hot spot deep in the mantle
C)old, deeply eroded composite cones built before the Pacific Ocean existed
D)old, deeply eroded, basaltic shield volcanoes built when western North America was over the present-day site of the Hawaiian hot spot

Question

Quizplus · Accepted Answer

The Cascade volcanoes from Mt. Shasta to Mt. Garibaldi are young and active composite volcanoes. They are located on a continental margin above a subduction zone where the Juan de Fuca plate is sinking beneath the North American plate. This produces magma that rises up to feed the volcanoes.

Mount StHelens and the Other Cascade Volcanoes from Mt