The Cascade volcanoes that run from northern California to southern British Columbia aren't exactly the most active volcanoes on Earth. While other places like Kamchatka in Russia and Indonesia tend to have multiple volcanoes erupting each day, only two volcanoes have erupted in the Cascades since 1900: Mount St. Helens in Washington and Lassen Peak in California.
Yet, for a volcanic arc like the Cascades, 120 years is nothing. In order to really understand what is happening in such a place, we need to look at longer timescales because the geologic processes of the Cascades work on deep time.
