 Complete the following phrase:  The Cascadia subduction zone is a long convergent plate boundary that separates the Juan de Fuca, Explorer, Gorda and North American Plates. Here, the oceanic crust of the Pacific Ocean sinks beneath North America at a rate of per year. Hot magma upwelling above the descending oceanic plate creates volcanoes, each of which erupts for a few million years. It is estimated that the subduction zone has existed for at least 37 million years; in that time it has created a line of volcanoes, called the Cascade Volcanic Arc, that stretches over along the subduction zone from Northern California to Vancouver Island. Several volcanoes in the arc are potentially active. All of the known historic eruptions in the arc have been in the United States. Two of the most recent were Lassen Peak in 1914 to 1921 and the 