Which of the following statements best describes the tectonic setting for Mount St. Helens and the other Cascade volcanoes?
A) A chain of young, active volcanoes built on a continental margin above a sinking slab of oceanic lithosphere
B) A chain of old, inactive volcanoes built while western North America moved over a mantle plume
C) Old, deeply eroded volcanoes built before the Pacific Ocean existed
D) Young, deeply eroded, basaltic volcanoes built when western North America was over the present-day site of the Hawaiian hot spot
Answer: A
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