Subduction of the Juan de Fuca Plate beneath the North American Pla...

Block diagram showing subduction of the Juan de Fuca Plate beneath the North American Plate along the Cascadia Trench, which is the western edge of the Cascadia subduction zone. Oceanic crust forms by eruptions along the Juan de Fuca Ridge. As the Juan de Fuca Plate drifts eastward, it cools, becomes more dense, and eventually dives under the less dense North American Plate at the Cascadia Trench. Water released from the subducting slab causes the overlying mantle to partially melt, forming magma that sustains the Cascade Range of volcanoes (black triangles).